2020-2-capstone-design2 / 2015104175

=============================
User Guide for AMDGPU Backend
=============================

.. contents::
:local:

.. toctree::
:hidden:

AMDGPU/AMDGPUAsmGFX7
AMDGPU/AMDGPUAsmGFX8
AMDGPU/AMDGPUAsmGFX9
AMDGPU/AMDGPUAsmGFX900
AMDGPU/AMDGPUAsmGFX904
AMDGPU/AMDGPUAsmGFX906
AMDGPU/AMDGPUAsmGFX908
AMDGPU/AMDGPUAsmGFX10
AMDGPU/AMDGPUAsmGFX1011
AMDGPUModifierSyntax
AMDGPUOperandSyntax
AMDGPUInstructionSyntax
AMDGPUInstructionNotation
AMDGPUDwarfExtensionsForHeterogeneousDebugging

Introduction
============

The AMDGPU backend provides ISA code generation for AMD GPUs, starting with the
R600 family up until the current GCN families. It lives in the
``llvm/lib/Target/AMDGPU`` directory.

LLVM
====

.. _amdgpu-target-triples:

Target Triples
--------------

Use the ``clang -target ---`` option to
specify the target triple:

.. table:: AMDGPU Architectures
:name: amdgpu-architecture-table

============ ==============================================================
Architecture Description
============ ==============================================================
``r600`` AMD GPUs HD2XXX-HD6XXX for graphics and compute shaders.
``amdgcn`` AMD GPUs GCN GFX6 onwards for graphics and compute shaders.
============ ==============================================================

.. table:: AMDGPU Vendors
:name: amdgpu-vendor-table

============ ==============================================================
Vendor Description
============ ==============================================================
``amd`` Can be used for all AMD GPU usage.
``mesa3d`` Can be used if the OS is ``mesa3d``.
============ ==============================================================

.. table:: AMDGPU Operating Systems
:name: amdgpu-os-table

============== ============================================================
OS Description
============== ============================================================
** Defaults to the *unknown* OS.
``amdhsa`` Compute kernels executed on HSA [HSA]_ compatible runtimes
such as AMD's ROCm [AMD-ROCm]_.
``amdpal`` Graphic shaders and compute kernels executed on AMD PAL
runtime.
``mesa3d`` Graphic shaders and compute kernels executed on Mesa 3D
runtime.
============== ============================================================

.. table:: AMDGPU Environments
:name: amdgpu-environment-table

============ ==============================================================
Environment Description
============ ==============================================================
** Default.
============ ==============================================================

.. _amdgpu-processors:

Processors
----------

Use the ``clang -mcpu `` option to specify the AMDGPU processor. The
names from both the *Processor* and *Alternative Processor* can be used.

.. table:: AMDGPU Processors
:name: amdgpu-processor-table

=========== =============== ============ ===== ================= ======= ======================
Processor Alternative Target dGPU/ Target ROCm Example
Processor Triple APU Features Support Products
Architecture Supported
[Default]
=========== =============== ============ ===== ================= ======= ======================
**Radeon HD 2000/3000 Series (R600)** [AMD-RADEON-HD-2000-3000]_
-----------------------------------------------------------------------------------------------
``r600`` ``r600`` dGPU
``r630`` ``r600`` dGPU
``rs880`` ``r600`` dGPU
``rv670`` ``r600`` dGPU
**Radeon HD 4000 Series (R700)** [AMD-RADEON-HD-4000]_
-----------------------------------------------------------------------------------------------
``rv710`` ``r600`` dGPU
``rv730`` ``r600`` dGPU
``rv770`` ``r600`` dGPU
**Radeon HD 5000 Series (Evergreen)** [AMD-RADEON-HD-5000]_
-----------------------------------------------------------------------------------------------
``cedar`` ``r600`` dGPU
``cypress`` ``r600`` dGPU
``juniper`` ``r600`` dGPU
``redwood`` ``r600`` dGPU
``sumo`` ``r600`` dGPU
**Radeon HD 6000 Series (Northern Islands)** [AMD-RADEON-HD-6000]_
-----------------------------------------------------------------------------------------------
``barts`` ``r600`` dGPU
``caicos`` ``r600`` dGPU
``cayman`` ``r600`` dGPU
``turks`` ``r600`` dGPU
**GCN GFX6 (Southern Islands (SI))** [AMD-GCN-GFX6]_
-----------------------------------------------------------------------------------------------
``gfx600`` - ``tahiti`` ``amdgcn`` dGPU
``gfx601`` - ``hainan`` ``amdgcn`` dGPU
- ``oland``
- ``pitcairn``
- ``verde``
**GCN GFX7 (Sea Islands (CI))** [AMD-GCN-GFX7]_
-----------------------------------------------------------------------------------------------
``gfx700`` - ``kaveri`` ``amdgcn`` APU - A6-7000
- A6 Pro-7050B
- A8-7100
- A8 Pro-7150B
- A10-7300
- A10 Pro-7350B
- FX-7500
- A8-7200P
- A10-7400P
- FX-7600P
``gfx701`` - ``hawaii`` ``amdgcn`` dGPU ROCm - FirePro W8100
- FirePro W9100
- FirePro S9150
- FirePro S9170
``gfx702`` ``amdgcn`` dGPU ROCm - Radeon R9 290
- Radeon R9 290x
- Radeon R390
- Radeon R390x
``gfx703`` - ``kabini`` ``amdgcn`` APU - E1-2100
- ``mullins`` - E1-2200
- E1-2500
- E2-3000
- E2-3800
- A4-5000
- A4-5100
- A6-5200
- A4 Pro-3340B
``gfx704`` - ``bonaire`` ``amdgcn`` dGPU - Radeon HD 7790
- Radeon HD 8770
- R7 260
- R7 260X
**GCN GFX8 (Volcanic Islands (VI))** [AMD-GCN-GFX8]_
-----------------------------------------------------------------------------------------------
``gfx801`` - ``carrizo`` ``amdgcn`` APU - xnack - A6-8500P
[on] - Pro A6-8500B
- A8-8600P
- Pro A8-8600B
- FX-8800P
- Pro A12-8800B
\ ``amdgcn`` APU - xnack ROCm - A10-8700P
[on] - Pro A10-8700B
- A10-8780P
\ ``amdgcn`` APU - xnack - A10-9600P
[on] - A10-9630P
- A12-9700P
- A12-9730P
- FX-9800P
- FX-9830P
\ ``amdgcn`` APU - xnack - E2-9010
[on] - A6-9210
- A9-9410
``gfx802`` - ``iceland`` ``amdgcn`` dGPU - xnack ROCm - FirePro S7150
- ``tonga`` [off] - FirePro S7100
- FirePro W7100
- Radeon R285
- Radeon R9 380
- Radeon R9 385
- Mobile FirePro
M7170
``gfx803`` - ``fiji`` ``amdgcn`` dGPU - xnack ROCm - Radeon R9 Nano
[off] - Radeon R9 Fury
- Radeon R9 FuryX
- Radeon Pro Duo
- FirePro S9300x2
- Radeon Instinct MI8
\ - ``polaris10`` ``amdgcn`` dGPU - xnack ROCm - Radeon RX 470
[off] - Radeon RX 480
- Radeon Instinct MI6
\ - ``polaris11`` ``amdgcn`` dGPU - xnack ROCm - Radeon RX 460
[off]
``gfx810`` - ``stoney`` ``amdgcn`` APU - xnack
[on]
**GCN GFX9** [AMD-GCN-GFX9]_
-----------------------------------------------------------------------------------------------
``gfx900`` ``amdgcn`` dGPU - xnack ROCm - Radeon Vega
[off] Frontier Edition
- Radeon RX Vega 56
- Radeon RX Vega 64
- Radeon RX Vega 64
Liquid
- Radeon Instinct MI25
``gfx902`` ``amdgcn`` APU - xnack - Ryzen 3 2200G
[on] - Ryzen 5 2400G
``gfx904`` ``amdgcn`` dGPU - xnack *TBA*
[off]
.. TODO::
Add product
names.
``gfx906`` ``amdgcn`` dGPU - xnack - Radeon Instinct MI50
[off] - Radeon Instinct MI60
- sram-ecc - Radeon VII
[off] - Radeon Pro VII
``gfx908`` ``amdgcn`` dGPU - xnack *TBA*
[off]
- sram-ecc
[on]
.. TODO::
Add product
names.
``gfx909`` ``amdgcn`` APU - xnack *TBA*
[on]
.. TODO::
Add product
names.
**GCN GFX10** [AMD-GCN-GFX10]_
-----------------------------------------------------------------------------------------------
``gfx1010`` ``amdgcn`` dGPU - xnack - Radeon RX 5700
[off] - Radeon RX 5700 XT
- wavefrontsize64 - Radeon Pro 5600 XT
[off]
- cumode
[off]
``gfx1011`` ``amdgcn`` dGPU - xnack - Radeon Pro 5600M
[off]
- wavefrontsize64
[off]
- cumode
[off]
``gfx1012`` ``amdgcn`` dGPU - xnack - Radeon RX 5500
[off] - Radeon RX 5500 XT
- wavefrontsize64
[off]
- cumode
[off]
``gfx1030`` ``amdgcn`` dGPU - wavefrontsize64 *TBA*
[off]
- cumode
[off]
.. TODO
Add product
names.
``gfx1031`` ``amdgcn`` dGPU - wavefrontsize64 *TBA*
[off]
- cumode
[off]
.. TODO
Add product
names.
=========== =============== ============ ===== ================= ======= ======================

.. _amdgpu-target-features:

Target Features
---------------

Target features control how code is generated to support certain
processor specific features. Not all target features are supported by
all processors. The runtime must ensure that the features supported by
the device used to execute the code match the features enabled when
generating the code. A mismatch of features may result in incorrect
execution, or a reduction in performance.

The target features supported by each processor, and the default value
used if not specified explicitly, is listed in
:ref:`amdgpu-processor-table`.

Use the ``clang -m[no-]`` option to specify the AMDGPU
target features.

For example:

``-mxnack``
Enable the ``xnack`` feature.
``-mno-xnack``
Disable the ``xnack`` feature.

.. table:: AMDGPU Target Features
:name: amdgpu-target-feature-table

====================== ==================================================
Target Feature Description
====================== ==================================================
-m[no-]xnack Enable/disable generating code that has
memory clauses that are compatible with
having XNACK replay enabled.

This is used for demand paging and page
migration. If XNACK replay is enabled in
the device, then if a page fault occurs
the code may execute incorrectly if the
``xnack`` feature is not enabled. Executing
code that has the feature enabled on a
device that does not have XNACK replay
enabled will execute correctly but may
be less performant than code with the
feature disabled.

-m[no-]sram-ecc Enable/disable generating code that assumes SRAM
ECC is enabled/disabled.

-m[no-]wavefrontsize64 Control the default wavefront size used when
generating code for kernels. When disabled
native wavefront size 32 is used, when enabled
wavefront size 64 is used.

-m[no-]cumode Control the default wavefront execution mode used
when generating code for kernels. When disabled
native WGP wavefront execution mode is used,
when enabled CU wavefront execution mode is used
(see :ref:`amdgpu-amdhsa-memory-model`).
====================== ==================================================

.. _amdgpu-address-spaces:

Address Spaces
--------------

The AMDGPU architecture supports a number of memory address spaces. The address
space names use the OpenCL standard names, with some additions.

The AMDGPU address spaces correspond to target architecture specific LLVM
address space numbers used in LLVM IR.

The AMDGPU address spaces are described in
:ref:`amdgpu-address-spaces-table`. Only 64-bit process address spaces are
supported for the ``amdgcn`` target.

.. table:: AMDGPU Address Spaces
:name: amdgpu-address-spaces-table

================================= =============== =========== ================ ======= ============================
.. 64-Bit Process Address Space
--------------------------------- --------------- ----------- ---------------- ------------------------------------
Address Space Name LLVM IR Address HSA Segment Hardware Address NULL Value
Space Number Name Name Size
================================= =============== =========== ================ ======= ============================
Generic 0 flat flat 64 0x0000000000000000
Global 1 global global 64 0x0000000000000000
Region 2 N/A GDS 32 *not implemented for AMDHSA*
Local 3 group LDS 32 0xFFFFFFFF
Constant 4 constant *same as global* 64 0x0000000000000000
Private 5 private scratch 32 0xFFFFFFFF
Constant 32-bit 6 *TODO* 0x00000000
Buffer Fat Pointer (experimental) 7 *TODO*
================================= =============== =========== ================ ======= ============================

**Generic**
The generic address space uses the hardware flat address support available in
GFX7-GFX10. This uses two fixed ranges of virtual addresses (the private and
local apertures), that are outside the range of addressable global memory, to
map from a flat address to a private or local address.

FLAT instructions can take a flat address and access global, private
(scratch), and group (LDS) memory depending on if the address is within one
of the aperture ranges. Flat access to scratch requires hardware aperture
setup and setup in the kernel prologue (see
:ref:`amdgpu-amdhsa-kernel-prolog-flat-scratch`). Flat access to LDS requires
hardware aperture setup and M0 (GFX7-GFX8) register setup (see
:ref:`amdgpu-amdhsa-kernel-prolog-m0`).

To convert between a private or group address space address (termed a segment
address) and a flat address the base address of the corresponding aperture
can be used. For GFX7-GFX8 these are available in the
:ref:`amdgpu-amdhsa-hsa-aql-queue` the address of which can be obtained with
Queue Ptr SGPR (see :ref:`amdgpu-amdhsa-initial-kernel-execution-state`). For
GFX9-GFX10 the aperture base addresses are directly available as inline
constant registers ``SRC_SHARED_BASE/LIMIT`` and ``SRC_PRIVATE_BASE/LIMIT``.
In 64-bit address mode the aperture sizes are 2^32 bytes and the base is
aligned to 2^32 which makes it easier to convert from flat to segment or
segment to flat.

A global address space address has the same value when used as a flat address
so no conversion is needed.

**Global and Constant**
The global and constant address spaces both use global virtual addresses,
which are the same virtual address space used by the CPU. However, some
virtual addresses may only be accessible to the CPU, some only accessible
by the GPU, and some by both.

Using the constant address space indicates that the data will not change
during the execution of the kernel. This allows scalar read instructions to
be used. The vector and scalar L1 caches are invalidated of volatile data
before each kernel dispatch execution to allow constant memory to change
values between kernel dispatches.

**Region**
The region address space uses the hardware Global Data Store (GDS). All
wavefronts executing on the same device will access the same memory for any
given region address. However, the same region address accessed by wavefronts
executing on different devices will access different memory. It is higher
performance than global memory. It is allocated by the runtime. The data
store (DS) instructions can be used to access it.

**Local**
The local address space uses the hardware Local Data Store (LDS) which is
automatically allocated when the hardware creates the wavefronts of a
work-group, and freed when all the wavefronts of a work-group have
terminated. All wavefronts belonging to the same work-group will access the
same memory for any given local address. However, the same local address
accessed by wavefronts belonging to different work-groups will access
different memory. It is higher performance than global memory. The data store
(DS) instructions can be used to access it.

**Private**
The private address space uses the hardware scratch memory support which
automatically allocates memory when it creates a wavefront and frees it when
a wavefronts terminates. The memory accessed by a lane of a wavefront for any
given private address will be different to the memory accessed by another lane
of the same or different wavefront for the same private address.

If a kernel dispatch uses scratch, then the hardware allocates memory from a
pool of backing memory allocated by the runtime for each wavefront. The lanes
of the wavefront access this using dword (4 byte) interleaving. The mapping
used from private address to backing memory address is:

``wavefront-scratch-base +
((private-address / 4) * wavefront-size * 4) +
(wavefront-lane-id * 4) + (private-address % 4)``

If each lane of a wavefront accesses the same private address, the
interleaving results in adjacent dwords being accessed and hence requires
fewer cache lines to be fetched.

There are different ways that the wavefront scratch base address is
determined by a wavefront (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

Scratch memory can be accessed in an interleaved manner using buffer
instructions with the scratch buffer descriptor and per wavefront scratch
offset, by the scratch instructions, or by flat instructions. Multi-dword
access is not supported except by flat and scratch instructions in
GFX9-GFX10.

**Constant 32-bit**
*TODO*

**Buffer Fat Pointer**
The buffer fat pointer is an experimental address space that is currently
unsupported in the backend. It exposes a non-integral pointer that is in
the future intended to support the modelling of 128-bit buffer descriptors
plus a 32-bit offset into the buffer (in total encapsulating a 160-bit
*pointer*), allowing normal LLVM load/store/atomic operations to be used to
model the buffer descriptors used heavily in graphics workloads targeting
the backend.

.. _amdgpu-memory-scopes:

Memory Scopes
-------------

This section provides LLVM memory synchronization scopes supported by the AMDGPU
backend memory model when the target triple OS is ``amdhsa`` (see
:ref:`amdgpu-amdhsa-memory-model` and :ref:`amdgpu-target-triples`).

The memory model supported is based on the HSA memory model [HSA]_ which is
based in turn on HRF-indirect with scope inclusion [HRF]_. The happens-before
relation is transitive over the synchronizes-with relation independent of scope
and synchronizes-with allows the memory scope instances to be inclusive (see
table :ref:`amdgpu-amdhsa-llvm-sync-scopes-table`).

This is different to the OpenCL [OpenCL]_ memory model which does not have scope
inclusion and requires the memory scopes to exactly match. However, this
is conservatively correct for OpenCL.

.. table:: AMDHSA LLVM Sync Scopes
:name: amdgpu-amdhsa-llvm-sync-scopes-table

======================= ===================================================
LLVM Sync Scope Description
======================= ===================================================
*none* The default: ``system``.

Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:

- ``system``.
- ``agent`` and executed by a thread on the same
agent.
- ``workgroup`` and executed by a thread in the
same work-group.
- ``wavefront`` and executed by a thread in the
same wavefront.

``agent`` Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:

- ``system`` or ``agent`` and executed by a thread
on the same agent.
- ``workgroup`` and executed by a thread in the
same work-group.
- ``wavefront`` and executed by a thread in the
same wavefront.

``workgroup`` Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:

- ``system``, ``agent`` or ``workgroup`` and
executed by a thread in the same work-group.
- ``wavefront`` and executed by a thread in the
same wavefront.

``wavefront`` Synchronizes with, and participates in modification
and seq_cst total orderings with, other operations
(except image operations) for all address spaces
(except private, or generic that accesses private)
provided the other operation's sync scope is:

- ``system``, ``agent``, ``workgroup`` or
``wavefront`` and executed by a thread in the
same wavefront.

``singlethread`` Only synchronizes with and participates in
modification and seq_cst total orderings with,
other operations (except image operations) running
in the same thread for all address spaces (for
example, in signal handlers).

``one-as`` Same as ``system`` but only synchronizes with other
operations within the same address space.

``agent-one-as`` Same as ``agent`` but only synchronizes with other
operations within the same address space.

``workgroup-one-as`` Same as ``workgroup`` but only synchronizes with
other operations within the same address space.

``wavefront-one-as`` Same as ``wavefront`` but only synchronizes with
other operations within the same address space.

``singlethread-one-as`` Same as ``singlethread`` but only synchronizes with
other operations within the same address space.
======================= ===================================================

LLVM IR Intrinsics
------------------

The AMDGPU backend implements the following LLVM IR intrinsics.

*This section is WIP.*

.. TODO::

List AMDGPU intrinsics.

LLVM IR Attributes
------------------

The AMDGPU backend supports the following LLVM IR attributes.

.. table:: AMDGPU LLVM IR Attributes
:name: amdgpu-llvm-ir-attributes-table

======================================= ==========================================================
LLVM Attribute Description
======================================= ==========================================================
"amdgpu-flat-work-group-size"="min,max" Specify the minimum and maximum flat work group sizes that
will be specified when the kernel is dispatched. Generated
by the ``amdgpu_flat_work_group_size`` CLANG attribute [CLANG-ATTR]_.
"amdgpu-implicitarg-num-bytes"="n" Number of kernel argument bytes to add to the kernel
argument block size for the implicit arguments. This
varies by OS and language (for OpenCL see
:ref:`opencl-kernel-implicit-arguments-appended-for-amdhsa-os-table`).
"amdgpu-num-sgpr"="n" Specifies the number of SGPRs to use. Generated by
the ``amdgpu_num_sgpr`` CLANG attribute [CLANG-ATTR]_.
"amdgpu-num-vgpr"="n" Specifies the number of VGPRs to use. Generated by the
``amdgpu_num_vgpr`` CLANG attribute [CLANG-ATTR]_.
"amdgpu-waves-per-eu"="m,n" Specify the minimum and maximum number of waves per
execution unit. Generated by the ``amdgpu_waves_per_eu``
CLANG attribute [CLANG-ATTR]_.
"amdgpu-ieee" true/false. Specify whether the function expects the IEEE field of the
mode register to be set on entry. Overrides the default for
the calling convention.
"amdgpu-dx10-clamp" true/false. Specify whether the function expects the DX10_CLAMP field of
the mode register to be set on entry. Overrides the default
for the calling convention.
======================================= ==========================================================

.. _amdgpu-elf-code-object:

ELF Code Object
===============

The AMDGPU backend generates a standard ELF [ELF]_ relocatable code object that
can be linked by ``lld`` to produce a standard ELF shared code object which can
be loaded and executed on an AMDGPU target.

.. _amdgpu-elf-header:

Header
------

The AMDGPU backend uses the following ELF header:

.. table:: AMDGPU ELF Header
:name: amdgpu-elf-header-table

========================== ===============================
Field Value
========================== ===============================
``e_ident[EI_CLASS]`` ``ELFCLASS64``
``e_ident[EI_DATA]`` ``ELFDATA2LSB``
``e_ident[EI_OSABI]`` - ``ELFOSABI_NONE``
- ``ELFOSABI_AMDGPU_HSA``
- ``ELFOSABI_AMDGPU_PAL``
- ``ELFOSABI_AMDGPU_MESA3D``
``e_ident[EI_ABIVERSION]`` - ``ELFABIVERSION_AMDGPU_HSA``
- ``ELFABIVERSION_AMDGPU_PAL``
- ``ELFABIVERSION_AMDGPU_MESA3D``
``e_type`` - ``ET_REL``
- ``ET_DYN``
``e_machine`` ``EM_AMDGPU``
``e_entry`` 0
``e_flags`` See :ref:`amdgpu-elf-header-e_flags-table`
========================== ===============================

..

.. table:: AMDGPU ELF Header Enumeration Values
:name: amdgpu-elf-header-enumeration-values-table

=============================== =====
Name Value
=============================== =====
``EM_AMDGPU`` 224
``ELFOSABI_NONE`` 0
``ELFOSABI_AMDGPU_HSA`` 64
``ELFOSABI_AMDGPU_PAL`` 65
``ELFOSABI_AMDGPU_MESA3D`` 66
``ELFABIVERSION_AMDGPU_HSA`` 1
``ELFABIVERSION_AMDGPU_PAL`` 0
``ELFABIVERSION_AMDGPU_MESA3D`` 0
=============================== =====

``e_ident[EI_CLASS]``
The ELF class is:

* ``ELFCLASS32`` for ``r600`` architecture.

* ``ELFCLASS64`` for ``amdgcn`` architecture which only supports 64-bit
process address space applications.

``e_ident[EI_DATA]``
All AMDGPU targets use ``ELFDATA2LSB`` for little-endian byte ordering.

``e_ident[EI_OSABI]``
One of the following AMDGPU target architecture specific OS ABIs
(see :ref:`amdgpu-os-table`):

* ``ELFOSABI_NONE`` for *unknown* OS.

* ``ELFOSABI_AMDGPU_HSA`` for ``amdhsa`` OS.

* ``ELFOSABI_AMDGPU_PAL`` for ``amdpal`` OS.

* ``ELFOSABI_AMDGPU_MESA3D`` for ``mesa3D`` OS.

``e_ident[EI_ABIVERSION]``
The ABI version of the AMDGPU target architecture specific OS ABI to which the code
object conforms:

* ``ELFABIVERSION_AMDGPU_HSA`` is used to specify the version of AMD HSA
runtime ABI.

* ``ELFABIVERSION_AMDGPU_PAL`` is used to specify the version of AMD PAL
runtime ABI.

* ``ELFABIVERSION_AMDGPU_MESA3D`` is used to specify the version of AMD MESA
3D runtime ABI.

``e_type``
Can be one of the following values:

``ET_REL``
The type produced by the AMDGPU backend compiler as it is relocatable code
object.

``ET_DYN``
The type produced by the linker as it is a shared code object.

The AMD HSA runtime loader requires a ``ET_DYN`` code object.

``e_machine``
The value ``EM_AMDGPU`` is used for the machine for all processors supported
by the ``r600`` and ``amdgcn`` architectures (see
:ref:`amdgpu-processor-table`). The specific processor is specified in the
``EF_AMDGPU_MACH`` bit field of the ``e_flags`` (see
:ref:`amdgpu-elf-header-e_flags-table`).

``e_entry``
The entry point is 0 as the entry points for individual kernels must be
selected in order to invoke them through AQL packets.

``e_flags``
The AMDGPU backend uses the following ELF header flags:

.. table:: AMDGPU ELF Header ``e_flags``
:name: amdgpu-elf-header-e_flags-table

================================= ========== =============================
Name Value Description
================================= ========== =============================
**AMDGPU Processor Flag** See :ref:`amdgpu-processor-table`.
-------------------------------------------- -----------------------------
``EF_AMDGPU_MACH`` 0x000000ff AMDGPU processor selection
mask for
``EF_AMDGPU_MACH_xxx`` values
defined in
:ref:`amdgpu-ef-amdgpu-mach-table`.
``EF_AMDGPU_XNACK`` 0x00000100 Indicates if the ``xnack``
target feature is
enabled for all code
contained in the code object.
If the processor
does not support the
``xnack`` target
feature then must
be 0.
See
:ref:`amdgpu-target-features`.
``EF_AMDGPU_SRAM_ECC`` 0x00000200 Indicates if the ``sram-ecc``
target feature is
enabled for all code
contained in the code object.
If the processor
does not support the
``sram-ecc`` target
feature then must
be 0.
See
:ref:`amdgpu-target-features`.
================================= ========== =============================

.. table:: AMDGPU ``EF_AMDGPU_MACH`` Values
:name: amdgpu-ef-amdgpu-mach-table

================================= ========== =============================
Name Value Description (see
:ref:`amdgpu-processor-table`)
================================= ========== =============================
``EF_AMDGPU_MACH_NONE`` 0x000 *not specified*
``EF_AMDGPU_MACH_R600_R600`` 0x001 ``r600``
``EF_AMDGPU_MACH_R600_R630`` 0x002 ``r630``
``EF_AMDGPU_MACH_R600_RS880`` 0x003 ``rs880``
``EF_AMDGPU_MACH_R600_RV670`` 0x004 ``rv670``
``EF_AMDGPU_MACH_R600_RV710`` 0x005 ``rv710``
``EF_AMDGPU_MACH_R600_RV730`` 0x006 ``rv730``
``EF_AMDGPU_MACH_R600_RV770`` 0x007 ``rv770``
``EF_AMDGPU_MACH_R600_CEDAR`` 0x008 ``cedar``
``EF_AMDGPU_MACH_R600_CYPRESS`` 0x009 ``cypress``
``EF_AMDGPU_MACH_R600_JUNIPER`` 0x00a ``juniper``
``EF_AMDGPU_MACH_R600_REDWOOD`` 0x00b ``redwood``
``EF_AMDGPU_MACH_R600_SUMO`` 0x00c ``sumo``
``EF_AMDGPU_MACH_R600_BARTS`` 0x00d ``barts``
``EF_AMDGPU_MACH_R600_CAICOS`` 0x00e ``caicos``
``EF_AMDGPU_MACH_R600_CAYMAN`` 0x00f ``cayman``
``EF_AMDGPU_MACH_R600_TURKS`` 0x010 ``turks``
*reserved* 0x011 - Reserved for ``r600``
0x01f architecture processors.
``EF_AMDGPU_MACH_AMDGCN_GFX600`` 0x020 ``gfx600``
``EF_AMDGPU_MACH_AMDGCN_GFX601`` 0x021 ``gfx601``
``EF_AMDGPU_MACH_AMDGCN_GFX700`` 0x022 ``gfx700``
``EF_AMDGPU_MACH_AMDGCN_GFX701`` 0x023 ``gfx701``
``EF_AMDGPU_MACH_AMDGCN_GFX702`` 0x024 ``gfx702``
``EF_AMDGPU_MACH_AMDGCN_GFX703`` 0x025 ``gfx703``
``EF_AMDGPU_MACH_AMDGCN_GFX704`` 0x026 ``gfx704``
*reserved* 0x027 Reserved.
``EF_AMDGPU_MACH_AMDGCN_GFX801`` 0x028 ``gfx801``
``EF_AMDGPU_MACH_AMDGCN_GFX802`` 0x029 ``gfx802``
``EF_AMDGPU_MACH_AMDGCN_GFX803`` 0x02a ``gfx803``
``EF_AMDGPU_MACH_AMDGCN_GFX810`` 0x02b ``gfx810``
``EF_AMDGPU_MACH_AMDGCN_GFX900`` 0x02c ``gfx900``
``EF_AMDGPU_MACH_AMDGCN_GFX902`` 0x02d ``gfx902``
``EF_AMDGPU_MACH_AMDGCN_GFX904`` 0x02e ``gfx904``
``EF_AMDGPU_MACH_AMDGCN_GFX906`` 0x02f ``gfx906``
``EF_AMDGPU_MACH_AMDGCN_GFX908`` 0x030 ``gfx908``
``EF_AMDGPU_MACH_AMDGCN_GFX909`` 0x031 ``gfx909``
*reserved* 0x032 Reserved.
``EF_AMDGPU_MACH_AMDGCN_GFX1010`` 0x033 ``gfx1010``
``EF_AMDGPU_MACH_AMDGCN_GFX1011`` 0x034 ``gfx1011``
``EF_AMDGPU_MACH_AMDGCN_GFX1012`` 0x035 ``gfx1012``
``EF_AMDGPU_MACH_AMDGCN_GFX1030`` 0x036 ``gfx1030``
``EF_AMDGPU_MACH_AMDGCN_GFX1031`` 0x037 ``gfx1031``
================================= ========== =============================

Sections
--------

An AMDGPU target ELF code object has the standard ELF sections which include:

.. table:: AMDGPU ELF Sections
:name: amdgpu-elf-sections-table

================== ================ =================================
Name Type Attributes
================== ================ =================================
``.bss`` ``SHT_NOBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.data`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.debug_``\ *\** ``SHT_PROGBITS`` *none*
``.dynamic`` ``SHT_DYNAMIC`` ``SHF_ALLOC``
``.dynstr`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.dynsym`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.got`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_WRITE``
``.hash`` ``SHT_HASH`` ``SHF_ALLOC``
``.note`` ``SHT_NOTE`` *none*
``.rela``\ *name* ``SHT_RELA`` *none*
``.rela.dyn`` ``SHT_RELA`` *none*
``.rodata`` ``SHT_PROGBITS`` ``SHF_ALLOC``
``.shstrtab`` ``SHT_STRTAB`` *none*
``.strtab`` ``SHT_STRTAB`` *none*
``.symtab`` ``SHT_SYMTAB`` *none*
``.text`` ``SHT_PROGBITS`` ``SHF_ALLOC`` + ``SHF_EXECINSTR``
================== ================ =================================

These sections have their standard meanings (see [ELF]_) and are only generated
if needed.

``.debug``\ *\**
The standard DWARF sections. See :ref:`amdgpu-dwarf-debug-information` for
information on the DWARF produced by the AMDGPU backend.

``.dynamic``, ``.dynstr``, ``.dynsym``, ``.hash``
The standard sections used by a dynamic loader.

``.note``
See :ref:`amdgpu-note-records` for the note records supported by the AMDGPU
backend.

``.rela``\ *name*, ``.rela.dyn``
For relocatable code objects, *name* is the name of the section that the
relocation records apply. For example, ``.rela.text`` is the section name for
relocation records associated with the ``.text`` section.

For linked shared code objects, ``.rela.dyn`` contains all the relocation
records from each of the relocatable code object's ``.rela``\ *name* sections.

See :ref:`amdgpu-relocation-records` for the relocation records supported by
the AMDGPU backend.

``.text``
The executable machine code for the kernels and functions they call. Generated
as position independent code. See :ref:`amdgpu-code-conventions` for
information on conventions used in the isa generation.

.. _amdgpu-note-records:

Note Records
------------

The AMDGPU backend code object contains ELF note records in the ``.note``
section. The set of generated notes and their semantics depend on the code
object version; see :ref:`amdgpu-note-records-v2` and
:ref:`amdgpu-note-records-v3`.

As required by ``ELFCLASS32`` and ``ELFCLASS64``, minimal zero-byte padding
must be generated after the ``name`` field to ensure the ``desc`` field is 4
byte aligned. In addition, minimal zero-byte padding must be generated to
ensure the ``desc`` field size is a multiple of 4 bytes. The ``sh_addralign``
field of the ``.note`` section must be at least 4 to indicate at least 8 byte
alignment.

.. _amdgpu-note-records-v2:

Code Object V2 Note Records (-mattr=-code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the notes generated with the
default configuration (Code Object V3) see :ref:`amdgpu-note-records-v3`.

The AMDGPU backend code object uses the following ELF note record in the
``.note`` section when compiling for Code Object V2 (-mattr=-code-object-v3).

Additional note records may be present, but any which are not documented here
are deprecated and should not be used.

.. table:: AMDGPU Code Object V2 ELF Note Records
:name: amdgpu-elf-note-records-table-v2

===== ============================== ======================================
Name Type Description
===== ============================== ======================================
"AMD" ``NT_AMD_AMDGPU_HSA_METADATA``
===== ============================== ======================================

..

.. table:: AMDGPU Code Object V2 ELF Note Record Enumeration Values
:name: amdgpu-elf-note-record-enumeration-values-table-v2

============================== =====
Name Value
============================== =====
*reserved* 0-9
``NT_AMD_AMDGPU_HSA_METADATA`` 10
*reserved* 11
============================== =====

``NT_AMD_AMDGPU_HSA_METADATA``
Specifies extensible metadata associated with the code objects executed on HSA
[HSA]_ compatible runtimes such as AMD's ROCm [AMD-ROCm]_. It is required when
the target triple OS is ``amdhsa`` (see :ref:`amdgpu-target-triples`). See
:ref:`amdgpu-amdhsa-code-object-metadata-v2` for the syntax of the code
object metadata string.

.. _amdgpu-note-records-v3:

Code Object V3 Note Records (-mattr=+code-object-v3)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The AMDGPU backend code object uses the following ELF note record in the
``.note`` section when compiling for Code Object V3 (-mattr=+code-object-v3).

Additional note records may be present, but any which are not documented here
are deprecated and should not be used.

.. table:: AMDGPU Code Object V3 ELF Note Records
:name: amdgpu-elf-note-records-table-v3

======== ============================== ======================================
Name Type Description
======== ============================== ======================================
"AMDGPU" ``NT_AMDGPU_METADATA`` Metadata in Message Pack [MsgPack]_
binary format.
======== ============================== ======================================

..

.. table:: AMDGPU Code Object V3 ELF Note Record Enumeration Values
:name: amdgpu-elf-note-record-enumeration-values-table-v3

============================== =====
Name Value
============================== =====
*reserved* 0-31
``NT_AMDGPU_METADATA`` 32
============================== =====

``NT_AMDGPU_METADATA``
Specifies extensible metadata associated with an AMDGPU code
object. It is encoded as a map in the Message Pack [MsgPack]_ binary
data format. See :ref:`amdgpu-amdhsa-code-object-metadata-v3` for the
map keys defined for the ``amdhsa`` OS.

.. _amdgpu-symbols:

Symbols
-------

Symbols include the following:

.. table:: AMDGPU ELF Symbols
:name: amdgpu-elf-symbols-table

===================== ================== ================ ==================
Name Type Section Description
===================== ================== ================ ==================
*link-name* ``STT_OBJECT`` - ``.data`` Global variable
- ``.rodata``
- ``.bss``
*link-name*\ ``.kd`` ``STT_OBJECT`` - ``.rodata`` Kernel descriptor
*link-name* ``STT_FUNC`` - ``.text`` Kernel entry point
*link-name* ``STT_OBJECT`` - SHN_AMDGPU_LDS Global variable in LDS
===================== ================== ================ ==================

Global variable
Global variables both used and defined by the compilation unit.

If the symbol is defined in the compilation unit then it is allocated in the
appropriate section according to if it has initialized data or is readonly.

If the symbol is external then its section is ``STN_UNDEF`` and the loader
will resolve relocations using the definition provided by another code object
or explicitly defined by the runtime.

If the symbol resides in local/group memory (LDS) then its section is the
special processor specific section name ``SHN_AMDGPU_LDS``, and the
``st_value`` field describes alignment requirements as it does for common
symbols.

.. TODO::

Add description of linked shared object symbols. Seems undefined symbols
are marked as STT_NOTYPE.

Kernel descriptor
Every HSA kernel has an associated kernel descriptor. It is the address of the
kernel descriptor that is used in the AQL dispatch packet used to invoke the
kernel, not the kernel entry point. The layout of the HSA kernel descriptor is
defined in :ref:`amdgpu-amdhsa-kernel-descriptor`.

Kernel entry point
Every HSA kernel also has a symbol for its machine code entry point.

.. _amdgpu-relocation-records:

Relocation Records
------------------

AMDGPU backend generates ``Elf64_Rela`` relocation records. Supported
relocatable fields are:

``word32``
This specifies a 32-bit field occupying 4 bytes with arbitrary byte
alignment. These values use the same byte order as other word values in the
AMDGPU architecture.

``word64``
This specifies a 64-bit field occupying 8 bytes with arbitrary byte
alignment. These values use the same byte order as other word values in the
AMDGPU architecture.

Following notations are used for specifying relocation calculations:

**A**
Represents the addend used to compute the value of the relocatable field.

**G**
Represents the offset into the global offset table at which the relocation
entry's symbol will reside during execution.

**GOT**
Represents the address of the global offset table.

**P**
Represents the place (section offset for ``et_rel`` or address for ``et_dyn``)
of the storage unit being relocated (computed using ``r_offset``).

**S**
Represents the value of the symbol whose index resides in the relocation
entry. Relocations not using this must specify a symbol index of
``STN_UNDEF``.

**B**
Represents the base address of a loaded executable or shared object which is
the difference between the ELF address and the actual load address.
Relocations using this are only valid in executable or shared objects.

The following relocation types are supported:

.. table:: AMDGPU ELF Relocation Records
:name: amdgpu-elf-relocation-records-table

========================== ======= ===== ========== ==============================
Relocation Type Kind Value Field Calculation
========================== ======= ===== ========== ==============================
``R_AMDGPU_NONE`` 0 *none* *none*
``R_AMDGPU_ABS32_LO`` Static, 1 ``word32`` (S + A) & 0xFFFFFFFF
Dynamic
``R_AMDGPU_ABS32_HI`` Static, 2 ``word32`` (S + A) >> 32
Dynamic
``R_AMDGPU_ABS64`` Static, 3 ``word64`` S + A
Dynamic
``R_AMDGPU_REL32`` Static 4 ``word32`` S + A - P
``R_AMDGPU_REL64`` Static 5 ``word64`` S + A - P
``R_AMDGPU_ABS32`` Static, 6 ``word32`` S + A
Dynamic
``R_AMDGPU_GOTPCREL`` Static 7 ``word32`` G + GOT + A - P
``R_AMDGPU_GOTPCREL32_LO`` Static 8 ``word32`` (G + GOT + A - P) & 0xFFFFFFFF
``R_AMDGPU_GOTPCREL32_HI`` Static 9 ``word32`` (G + GOT + A - P) >> 32
``R_AMDGPU_REL32_LO`` Static 10 ``word32`` (S + A - P) & 0xFFFFFFFF
``R_AMDGPU_REL32_HI`` Static 11 ``word32`` (S + A - P) >> 32
*reserved* 12
``R_AMDGPU_RELATIVE64`` Dynamic 13 ``word64`` B + A
========================== ======= ===== ========== ==============================

``R_AMDGPU_ABS32_LO`` and ``R_AMDGPU_ABS32_HI`` are only supported by
the ``mesa3d`` OS, which does not support ``R_AMDGPU_ABS64``.

There is no current OS loader support for 32-bit programs and so
``R_AMDGPU_ABS32`` is not used.

.. _amdgpu-loaded-code-object-path-uniform-resource-identifier:

Loaded Code Object Path Uniform Resource Identifier (URI)
---------------------------------------------------------

The AMD GPU code object loader represents the path of the ELF shared object from
which the code object was loaded as a textual Unifom Resource Identifier (URI).
Note that the code object is the in memory loaded relocated form of the ELF
shared object. Multiple code objects may be loaded at different memory
addresses in the same process from the same ELF shared object.

The loaded code object path URI syntax is defined by the following BNF syntax:

.. code::

code_object_uri ::== file_uri | memory_uri
file_uri ::== "file://" file_path [ range_specifier ]
memory_uri ::== "memory://" process_id range_specifier
range_specifier ::== [ "#" | "?" ] "offset=" number "&" "size=" number
file_path ::== URI_ENCODED_OS_FILE_PATH
process_id ::== DECIMAL_NUMBER
number ::== HEX_NUMBER | DECIMAL_NUMBER | OCTAL_NUMBER

**number**
Is a C integral literal where hexadecimal values are prefixed by "0x" or "0X",
and octal values by "0".

**file_path**
Is the file's path specified as a URI encoded UTF-8 string. In URI encoding,
every character that is not in the regular expression ``[a-zA-Z0-9/_.~-]`` is
encoded as two uppercase hexadecimal digits proceeded by "%". Directories in
the path are separated by "/".

**offset**
Is a 0-based byte offset to the start of the code object. For a file URI, it
is from the start of the file specified by the ``file_path``, and if omitted
defaults to 0. For a memory URI, it is the memory address and is required.

**size**
Is the number of bytes in the code object. For a file URI, if omitted it
defaults to the size of the file. It is required for a memory URI.

**process_id**
Is the identity of the process owning the memory. For Linux it is the C
unsigned integral decimal literal for the process ID (PID).

For example:

.. code::

file:///dir1/dir2/file1
file:///dir3/dir4/file2#offset=0x2000&size=3000
memory://1234#offset=0x20000&size=3000

.. _amdgpu-dwarf-debug-information:

DWARF Debug Information
=======================

.. warning::

This section describes **provisional support** for AMDGPU DWARF [DWARF]_ that
is not currently fully implemented and is subject to change.

AMDGPU generates DWARF [DWARF]_ debugging information ELF sections (see
:ref:`amdgpu-elf-code-object`) which contain information that maps the code
object executable code and data to the source language constructs. It can be
used by tools such as debuggers and profilers. It uses features defined in
:doc:`AMDGPUDwarfExtensionsForHeterogeneousDebugging` that are made available in
DWARF Version 4 and DWARF Version 5 as an LLVM vendor extension.

This section defines the AMDGPU target architecture specific DWARF mappings.

.. _amdgpu-dwarf-register-identifier:

Register Identifier
-------------------

This section defines the AMDGPU target architecture register numbers used in
DWARF operation expressions (see DWARF Version 5 section 2.5 and
:ref:`amdgpu-dwarf-operation-expressions`) and Call Frame Information
instructions (see DWARF Version 5 section 6.4 and
:ref:`amdgpu-dwarf-call-frame-information`).

A single code object can contain code for kernels that have different wavefront
sizes. The vector registers and some scalar registers are based on the wavefront
size. AMDGPU defines distinct DWARF registers for each wavefront size. This
simplifies the consumer of the DWARF so that each register has a fixed size,
rather than being dynamic according to the wavefront size mode. Similarly,
distinct DWARF registers are defined for those registers that vary in size
according to the process address size. This allows a consumer to treat a
specific AMDGPU processor as a single architecture regardless of how it is
configured at run time. The compiler explicitly specifies the DWARF registers
that match the mode in which the code it is generating will be executed.

DWARF registers are encoded as numbers, which are mapped to architecture
registers. The mapping for AMDGPU is defined in
:ref:`amdgpu-dwarf-register-mapping-table`. All AMDGPU targets use the same
mapping.

.. table:: AMDGPU DWARF Register Mapping
:name: amdgpu-dwarf-register-mapping-table

============== ================= ======== ==================================
DWARF Register AMDGPU Register Bit Size Description
============== ================= ======== ==================================
0 PC_32 32 Program Counter (PC) when
executing in a 32-bit process
address space. Used in the CFI to
describe the PC of the calling
frame.
1 EXEC_MASK_32 32 Execution Mask Register when
executing in wavefront 32 mode.
2-15 *Reserved* *Reserved for highly accessed
registers using DWARF shortcut.*
16 PC_64 64 Program Counter (PC) when
executing in a 64-bit process
address space. Used in the CFI to
describe the PC of the calling
frame.
17 EXEC_MASK_64 64 Execution Mask Register when
executing in wavefront 64 mode.
18-31 *Reserved* *Reserved for highly accessed
registers using DWARF shortcut.*
32-95 SGPR0-SGPR63 32 Scalar General Purpose
Registers.
96-127 *Reserved* *Reserved for frequently accessed
registers using DWARF 1-byte ULEB.*
128 STATUS 32 Status Register.
129-511 *Reserved* *Reserved for future Scalar
Architectural Registers.*
512 VCC_32 32 Vector Condition Code Register
when executing in wavefront 32
mode.
513-1023 *Reserved* *Reserved for future Vector
Architectural Registers when
executing in wavefront 32 mode.*
768 VCC_64 64 Vector Condition Code Register
when executing in wavefront 64
mode.
769-1023 *Reserved* *Reserved for future Vector
Architectural Registers when
executing in wavefront 64 mode.*
1024-1087 *Reserved* *Reserved for padding.*
1088-1129 SGPR64-SGPR105 32 Scalar General Purpose Registers.
1130-1535 *Reserved* *Reserved for future Scalar
General Purpose Registers.*
1536-1791 VGPR0-VGPR255 32*32 Vector General Purpose Registers
when executing in wavefront 32
mode.
1792-2047 *Reserved* *Reserved for future Vector
General Purpose Registers when
executing in wavefront 32 mode.*
2048-2303 AGPR0-AGPR255 32*32 Vector Accumulation Registers
when executing in wavefront 32
mode.
2304-2559 *Reserved* *Reserved for future Vector
Accumulation Registers when
executing in wavefront 32 mode.*
2560-2815 VGPR0-VGPR255 64*32 Vector General Purpose Registers
when executing in wavefront 64
mode.
2816-3071 *Reserved* *Reserved for future Vector
General Purpose Registers when
executing in wavefront 64 mode.*
3072-3327 AGPR0-AGPR255 64*32 Vector Accumulation Registers
when executing in wavefront 64
mode.
3328-3583 *Reserved* *Reserved for future Vector
Accumulation Registers when
executing in wavefront 64 mode.*
============== ================= ======== ==================================

The vector registers are represented as the full size for the wavefront. They
are organized as consecutive dwords (32-bits), one per lane, with the dword at
the least significant bit position corresponding to lane 0 and so forth. DWARF
location expressions involving the ``DW_OP_LLVM_offset`` and
``DW_OP_LLVM_push_lane`` operations are used to select the part of the vector
register corresponding to the lane that is executing the current thread of
execution in languages that are implemented using a SIMD or SIMT execution
model.

If the wavefront size is 32 lanes then the wavefront 32 mode register
definitions are used. If the wavefront size is 64 lanes then the wavefront 64
mode register definitions are used. Some AMDGPU targets support executing in
both wavefront 32 and wavefront 64 mode. The register definitions corresponding
to the wavefront mode of the generated code will be used.

If code is generated to execute in a 32-bit process address space, then the
32-bit process address space register definitions are used. If code is generated
to execute in a 64-bit process address space, then the 64-bit process address
space register definitions are used. The ``amdgcn`` target only supports the
64-bit process address space.

.. _amdgpu-dwarf-address-class-identifier:

Address Class Identifier
------------------------

The DWARF address class represents the source language memory space. See DWARF
Version 5 section 2.12 which is updated by the *DWARF Extensions For
Heterogeneous Debugging* section :ref:`amdgpu-dwarf-segment_addresses`.

The DWARF address class mapping used for AMDGPU is defined in
:ref:`amdgpu-dwarf-address-class-mapping-table`.

.. table:: AMDGPU DWARF Address Class Mapping
:name: amdgpu-dwarf-address-class-mapping-table

========================= ====== =================
DWARF AMDGPU
-------------------------------- -----------------
Address Class Name Value Address Space
========================= ====== =================
``DW_ADDR_none`` 0x0000 Generic (Flat)
``DW_ADDR_LLVM_global`` 0x0001 Global
``DW_ADDR_LLVM_constant`` 0x0002 Global
``DW_ADDR_LLVM_group`` 0x0003 Local (group/LDS)
``DW_ADDR_LLVM_private`` 0x0004 Private (Scratch)
``DW_ADDR_AMDGPU_region`` 0x8000 Region (GDS)
========================= ====== =================

The DWARF address class values defined in the *DWARF Extensions For
Heterogeneous Debugging* section :ref:`amdgpu-dwarf-segment_addresses` are used.

In addition, ``DW_ADDR_AMDGPU_region`` is encoded as a vendor extension. This is
available for use for the AMD extension for access to the hardware GDS memory
which is scratchpad memory allocated per device.

For AMDGPU if no ``DW_AT_address_class`` attribute is present, then the default
address class of ``DW_ADDR_none`` is used.

See :ref:`amdgpu-dwarf-address-space-identifier` for information on the AMDGPU
mapping of DWARF address classes to DWARF address spaces, including address size
and NULL value.

.. _amdgpu-dwarf-address-space-identifier:

Address Space Identifier
------------------------

DWARF address spaces correspond to target architecture specific linear
addressable memory areas. See DWARF Version 5 section 2.12 and *DWARF Extensions
For Heterogeneous Debugging* section :ref:`amdgpu-dwarf-segment_addresses`.

The DWARF address space mapping used for AMDGPU is defined in
:ref:`amdgpu-dwarf-address-space-mapping-table`.

.. table:: AMDGPU DWARF Address Space Mapping
:name: amdgpu-dwarf-address-space-mapping-table

======================================= ===== ======= ======== ================= =======================
DWARF AMDGPU Notes
--------------------------------------- ----- ---------------- ----------------- -----------------------
Address Space Name Value Address Bit Size Address Space
--------------------------------------- ----- ------- -------- ----------------- -----------------------
.. 64-bit 32-bit
process process
address address
space space
======================================= ===== ======= ======== ================= =======================
``DW_ASPACE_none`` 0x00 8 4 Global *default address space*
``DW_ASPACE_AMDGPU_generic`` 0x01 8 4 Generic (Flat)
``DW_ASPACE_AMDGPU_region`` 0x02 4 4 Region (GDS)
``DW_ASPACE_AMDGPU_local`` 0x03 4 4 Local (group/LDS)
*Reserved* 0x04
``DW_ASPACE_AMDGPU_private_lane`` 0x05 4 4 Private (Scratch) *focused lane*
``DW_ASPACE_AMDGPU_private_wave`` 0x06 4 4 Private (Scratch) *unswizzled wavefront*
======================================= ===== ======= ======== ================= =======================

See :ref:`amdgpu-address-spaces` for information on the AMDGPU address spaces
including address size and NULL value.

The ``DW_ASPACE_none`` address space is the default target architecture address
space used in DWARF operations that do not specify an address space. It
therefore has to map to the global address space so that the ``DW_OP_addr*`` and
related operations can refer to addresses in the program code.

The ``DW_ASPACE_AMDGPU_generic`` address space allows location expressions to
specify the flat address space. If the address corresponds to an address in the
local address space, then it corresponds to the wavefront that is executing the
focused thread of execution. If the address corresponds to an address in the
private address space, then it corresponds to the lane that is executing the
focused thread of execution for languages that are implemented using a SIMD or
SIMT execution model.

.. note::

CUDA-like languages such as HIP that do not have address spaces in the
language type system, but do allow variables to be allocated in different
address spaces, need to explicitly specify the ``DW_ASPACE_AMDGPU_generic``
address space in the DWARF expression operations as the default address space
is the global address space.

The ``DW_ASPACE_AMDGPU_local`` address space allows location expressions to
specify the local address space corresponding to the wavefront that is executing
the focused thread of execution.

The ``DW_ASPACE_AMDGPU_private_lane`` address space allows location expressions
to specify the private address space corresponding to the lane that is executing
the focused thread of execution for languages that are implemented using a SIMD
or SIMT execution model.

The ``DW_ASPACE_AMDGPU_private_wave`` address space allows location expressions
to specify the unswizzled private address space corresponding to the wavefront
that is executing the focused thread of execution. The wavefront view of private
memory is the per wavefront unswizzled backing memory layout defined in
:ref:`amdgpu-address-spaces`, such that address 0 corresponds to the first
location for the backing memory of the wavefront (namely the address is not
offset by ``wavefront-scratch-base``). The following formula can be used to
convert from a ``DW_ASPACE_AMDGPU_private_lane`` address to a
``DW_ASPACE_AMDGPU_private_wave`` address:

::

private-address-wavefront =
((private-address-lane / 4) * wavefront-size * 4) +
(wavefront-lane-id * 4) + (private-address-lane % 4)

If the ``DW_ASPACE_AMDGPU_private_lane`` address is dword aligned, and the start
of the dwords for each lane starting with lane 0 is required, then this
simplifies to:

::

private-address-wavefront =
private-address-lane * wavefront-size

A compiler can use the ``DW_ASPACE_AMDGPU_private_wave`` address space to read a
complete spilled vector register back into a complete vector register in the
CFI. The frame pointer can be a private lane address which is dword aligned,
which can be shifted to multiply by the wavefront size, and then used to form a
private wavefront address that gives a location for a contiguous set of dwords,
one per lane, where the vector register dwords are spilled. The compiler knows
the wavefront size since it generates the code. Note that the type of the
address may have to be converted as the size of a
``DW_ASPACE_AMDGPU_private_lane`` address may be smaller than the size of a
``DW_ASPACE_AMDGPU_private_wave`` address.

.. _amdgpu-dwarf-lane-identifier:

Lane identifier
---------------

DWARF lane identifies specify a target architecture lane position for hardware
that executes in a SIMD or SIMT manner, and on which a source language maps its
threads of execution onto those lanes. The DWARF lane identifier is pushed by
the ``DW_OP_LLVM_push_lane`` DWARF expression operation. See DWARF Version 5
section 2.5 which is updated by *DWARF Extensions For Heterogeneous Debugging*
section :ref:`amdgpu-dwarf-operation-expressions`.

For AMDGPU, the lane identifier corresponds to the hardware lane ID of a
wavefront. It is numbered from 0 to the wavefront size minus 1.

Operation Expressions
---------------------

DWARF expressions are used to compute program values and the locations of
program objects. See DWARF Version 5 section 2.5 and
:ref:`amdgpu-dwarf-operation-expressions`.

DWARF location descriptions describe how to access storage which includes memory
and registers. When accessing storage on AMDGPU, bytes are ordered with least
significant bytes first, and bits are ordered within bytes with least
significant bits first.

For AMDGPU CFI expressions, ``DW_OP_LLVM_select_bit_piece`` is used to describe
unwinding vector registers that are spilled under the execution mask to memory:
the zero-single location description is the vector register, and the one-single
location description is the spilled memory location description. The
``DW_OP_LLVM_form_aspace_address`` is used to specify the address space of the
memory location description.

In AMDGPU expressions, ``DW_OP_LLVM_select_bit_piece`` is used by the
``DW_AT_LLVM_lane_pc`` attribute expression where divergent control flow is
controlled by the execution mask. An undefined location description together
with ``DW_OP_LLVM_extend`` is used to indicate the lane was not active on entry
to the subprogram. See :ref:`amdgpu-dwarf-dw-at-llvm-lane-pc` for an example.

Debugger Information Entry Attributes
-------------------------------------

This section describes how certain debugger information entry attributes are
used by AMDGPU. See the sections in DWARF Version 5 section 2 which are updated
by *DWARF Extensions For Heterogeneous Debugging* section
:ref:`amdgpu-dwarf-debugging-information-entry-attributes`.

.. _amdgpu-dwarf-dw-at-llvm-lane-pc:

``DW_AT_LLVM_lane_pc``
~~~~~~~~~~~~~~~~~~~~~~

For AMDGPU, the ``DW_AT_LLVM_lane_pc`` attribute is used to specify the program
location of the separate lanes of a SIMT thread.

If the lane is an active lane then this will be the same as the current program
location.

If the lane is inactive, but was active on entry to the subprogram, then this is
the program location in the subprogram at which execution of the lane is
conceptual positioned.

If the lane was not active on entry to the subprogram, then this will be the
undefined location. A client debugger can check if the lane is part of a valid
work-group by checking that the lane is in the range of the associated
work-group within the grid, accounting for partial work-groups. If it is not,
then the debugger can omit any information for the lane. Otherwise, the debugger
may repeatedly unwind the stack and inspect the ``DW_AT_LLVM_lane_pc`` of the
calling subprogram until it finds a non-undefined location. Conceptually the
lane only has the call frames that it has a non-undefined
``DW_AT_LLVM_lane_pc``.

The following example illustrates how the AMDGPU backend can generate a DWARF
location list expression for the nested ``IF/THEN/ELSE`` structures of the
following subprogram pseudo code for a target with 64 lanes per wavefront.

.. code::
:number-lines:

SUBPROGRAM X
BEGIN
a;
IF (c1) THEN
b;
IF (c2) THEN
c;
ELSE
d;
ENDIF
e;
ELSE
f;
ENDIF
g;
END

The AMDGPU backend may generate the following pseudo LLVM MIR to manipulate the
execution mask (``EXEC``) to linearize the control flow. The condition is
evaluated to make a mask of the lanes for which the condition evaluates to true.
First the ``THEN`` region is executed by setting the ``EXEC`` mask to the
logical ``AND`` of the current ``EXEC`` mask with the condition mask. Then the
``ELSE`` region is executed by negating the ``EXEC`` mask and logical ``AND`` of
the saved ``EXEC`` mask at the start of the region. After the ``IF/THEN/ELSE``
region the ``EXEC`` mask is restored to the value it had at the beginning of the
region. This is shown below. Other approaches are possible, but the basic
concept is the same.

.. code::
:number-lines:

$lex_start:
a;
%1 = EXEC
%2 = c1
$lex_1_start:
EXEC = %1 & %2
$if_1_then:
b;
%3 = EXEC
%4 = c2
$lex_1_1_start:
EXEC = %3 & %4
$lex_1_1_then:
c;
EXEC = ~EXEC & %3
$lex_1_1_else:
d;
EXEC = %3
$lex_1_1_end:
e;
EXEC = ~EXEC & %1
$lex_1_else:
f;
EXEC = %1
$lex_1_end:
g;
$lex_end:

To create the DWARF location list expression that defines the location
description of a vector of lane program locations, the LLVM MIR ``DBG_VALUE``
pseudo instruction can be used to annotate the linearized control flow. This can
be done by defining an artificial variable for the lane PC. The DWARF location
list expression created for it is used as the value of the
``DW_AT_LLVM_lane_pc`` attribute on the subprogram's debugger information entry.

A DWARF procedure is defined for each well nested structured control flow region
which provides the conceptual lane program location for a lane if it is not
active (namely it is divergent). The DWARF operation expression for each region
conceptually inherits the value of the immediately enclosing region and modifies
it according to the semantics of the region.

For an ``IF/THEN/ELSE`` region the divergent program location is at the start of
the region for the ``THEN`` region since it is executed first. For the ``ELSE``
region the divergent program location is at the end of the ``IF/THEN/ELSE``
region since the ``THEN`` region has completed.

The lane PC artificial variable is assigned at each region transition. It uses
the immediately enclosing region's DWARF procedure to compute the program
location for each lane assuming they are divergent, and then modifies the result
by inserting the current program location for each lane that the ``EXEC`` mask
indicates is active.

By having separate DWARF procedures for each region, they can be reused to
define the value for any nested region. This reduces the total size of the DWARF
operation expressions.

The following provides an example using pseudo LLVM MIR.

.. code::
:number-lines:

$lex_start:
DEFINE_DWARF %__uint_64 = DW_TAG_base_type[
DW_AT_name = "__uint64";
DW_AT_byte_size = 8;
DW_AT_encoding = DW_ATE_unsigned;
];
DEFINE_DWARF %__active_lane_pc = DW_TAG_dwarf_procedure[
DW_AT_name = "__active_lane_pc";
DW_AT_location = [
DW_OP_regx PC;
DW_OP_LLVM_extend 64, 64;
DW_OP_regval_type EXEC, %uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DEFINE_DWARF %__divergent_lane_pc = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc";
DW_AT_location = [
DW_OP_LLVM_undefined;
DW_OP_LLVM_extend 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_call_ref %__active_lane_pc;
];
a;
%1 = EXEC;
DBG_VALUE %1, $noreg, %__lex_1_save_exec;
%2 = c1;
$lex_1_start:
EXEC = %1 & %2;
$lex_1_then:
DEFINE_DWARF %__divergent_lane_pc_1_then = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_then";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_addrx &lex_1_start;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_then;
DW_OP_call_ref %__active_lane_pc;
];
b;
%3 = EXEC;
DBG_VALUE %3, %__lex_1_1_save_exec;
%4 = c2;
$lex_1_1_start:
EXEC = %3 & %4;
$lex_1_1_then:
DEFINE_DWARF %__divergent_lane_pc_1_1_then = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_1_then";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_then;
DW_OP_addrx &lex_1_1_start;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_1_then;
DW_OP_call_ref %__active_lane_pc;
];
c;
EXEC = ~EXEC & %3;
$lex_1_1_else:
DEFINE_DWARF %__divergent_lane_pc_1_1_else = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_1_else";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_then;
DW_OP_addrx &lex_1_1_end;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_1_else;
DW_OP_call_ref %__active_lane_pc;
];
d;
EXEC = %3;
$lex_1_1_end:
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_call_ref %__active_lane_pc;
];
e;
EXEC = ~EXEC & %1;
$lex_1_else:
DEFINE_DWARF %__divergent_lane_pc_1_else = DW_TAG_dwarf_procedure[
DW_AT_name = "__divergent_lane_pc_1_else";
DW_AT_location = DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_addrx &lex_1_end;
DW_OP_stack_value;
DW_OP_LLVM_extend 64, 64;
DW_OP_call_ref %__lex_1_save_exec;
DW_OP_deref_type 64, %__uint_64;
DW_OP_LLVM_select_bit_piece 64, 64;
];
];
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc, DIExpression[
DW_OP_call_ref %__divergent_lane_pc_1_else;
DW_OP_call_ref %__active_lane_pc;
];
f;
EXEC = %1;
$lex_1_end:
DBG_VALUE $noreg, $noreg, %DW_AT_LLVM_lane_pc DIExpression[
DW_OP_call_ref %__divergent_lane_pc;
DW_OP_call_ref %__active_lane_pc;
];
g;
$lex_end:

The DWARF procedure ``%__active_lane_pc`` is used to update the lane pc elements
that are active, with the current program location.

Artificial variables %__lex_1_save_exec and %__lex_1_1_save_exec are created for
the execution masks saved on entry to a region. Using the ``DBG_VALUE`` pseudo
instruction, location list entries will be created that describe where the
artificial variables are allocated at any given program location. The compiler
may allocate them to registers or spill them to memory.

The DWARF procedures for each region use the values of the saved execution mask
artificial variables to only update the lanes that are active on entry to the
region. All other lanes retain the value of the enclosing region where they were
last active. If they were not active on entry to the subprogram, then will have
the undefined location description.

Other structured control flow regions can be handled similarly. For example,
loops would set the divergent program location for the region at the end of the
loop. Any lanes active will be in the loop, and any lanes not active must have
exited the loop.

An ``IF/THEN/ELSEIF/ELSEIF/...`` region can be treated as a nest of
``IF/THEN/ELSE`` regions.

The DWARF procedures can use the active lane artificial variable described in
:ref:`amdgpu-dwarf-amdgpu-dw-at-llvm-active-lane` rather than the actual
``EXEC`` mask in order to support whole or quad wavefront mode.

.. _amdgpu-dwarf-amdgpu-dw-at-llvm-active-lane:

``DW_AT_LLVM_active_lane``
~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``DW_AT_LLVM_active_lane`` attribute on a subprogram debugger information
entry is used to specify the lanes that are conceptually active for a SIMT
thread.

The execution mask may be modified to implement whole or quad wavefront mode
operations. For example, all lanes may need to temporarily be made active to
execute a whole wavefront operation. Such regions would save the ``EXEC`` mask,
update it to enable the necessary lanes, perform the operations, and then
restore the ``EXEC`` mask from the saved value. While executing the whole
wavefront region, the conceptual execution mask is the saved value, not the
``EXEC`` value.

This is handled by defining an artificial variable for the active lane mask. The
active lane mask artificial variable would be the actual ``EXEC`` mask for
normal regions, and the saved execution mask for regions where the mask is
temporarily updated. The location list expression created for this artificial
variable is used to define the value of the ``DW_AT_LLVM_active_lane``
attribute.

``DW_AT_LLVM_augmentation``
~~~~~~~~~~~~~~~~~~~~~~~~~~~

For AMDGPU, the ``DW_AT_LLVM_augmentation`` attribute of a compilation unit
debugger information entry has the following value for the augmentation string:

::

[amdgpu:v0.0]

The "vX.Y" specifies the major X and minor Y version number of the AMDGPU
extensions used in the DWARF of the compilation unit. The version number
conforms to [SEMVER]_.

Call Frame Information
----------------------

DWARF Call Frame Information (CFI) describes how a consumer can virtually
*unwind* call frames in a running process or core dump. See DWARF Version 5
section 6.4 and :ref:`amdgpu-dwarf-call-frame-information`.

For AMDGPU, the Common Information Entry (CIE) fields have the following values:

1. ``augmentation`` string contains the following null-terminated UTF-8 string:

::

[amd:v0.0]

The ``vX.Y`` specifies the major X and minor Y version number of the AMDGPU
extensions used in this CIE or to the FDEs that use it. The version number
conforms to [SEMVER]_.

2. ``address_size`` for the ``Global`` address space is defined in
:ref:`amdgpu-dwarf-address-space-identifier`.

3. ``segment_selector_size`` is 0 as AMDGPU does not use a segment selector.

4. ``code_alignment_factor`` is 4 bytes.

.. TODO::

Add to :ref:`amdgpu-processor-table` table.

5. ``data_alignment_factor`` is 4 bytes.

.. TODO::

Add to :ref:`amdgpu-processor-table` table.

6. ``return_address_register`` is ``PC_32`` for 32-bit processes and ``PC_64``
for 64-bit processes defined in :ref:`amdgpu-dwarf-register-identifier`.

7. ``initial_instructions`` Since a subprogram X with fewer registers can be
called from subprogram Y that has more allocated, X will not change any of
the extra registers as it cannot access them. Therefore, the default rule
for all columns is ``same value``.

For AMDGPU the register number follows the numbering defined in
:ref:`amdgpu-dwarf-register-identifier`.

For AMDGPU the instructions are variable size. A consumer can subtract 1 from
the return address to get the address of a byte within the call site
instructions. See DWARF Version 5 section 6.4.4.

Accelerated Access
------------------

See DWARF Version 5 section 6.1.

Lookup By Name Section Header
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

See DWARF Version 5 section 6.1.1.4.1 and :ref:`amdgpu-dwarf-lookup-by-name`.

For AMDGPU the lookup by name section header table:

``augmentation_string_size`` (uword)

Set to the length of the ``augmentation_string`` value which is always a
multiple of 4.

``augmentation_string`` (sequence of UTF-8 characters)

Contains the following UTF-8 string null padded to a multiple of 4 bytes:

::

[amdgpu:v0.0]

The "vX.Y" specifies the major X and minor Y version number of the AMDGPU
extensions used in the DWARF of this index. The version number conforms to
[SEMVER]_.

.. note::

This is different to the DWARF Version 5 definition that requires the first
4 characters to be the vendor ID. But this is consistent with the other
augmentation strings and does allow multiple vendor contributions. However,
backwards compatibility may be more desirable.

Lookup By Address Section Header
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

See DWARF Version 5 section 6.1.2.

For AMDGPU the lookup by address section header table:

``address_size`` (ubyte)

Match the address size for the ``Global`` address space defined in
:ref:`amdgpu-dwarf-address-space-identifier`.

``segment_selector_size`` (ubyte)

AMDGPU does not use a segment selector so this is 0. The entries in the
``.debug_aranges`` do not have a segment selector.

Line Number Information
-----------------------

See DWARF Version 5 section 6.2 and :ref:`amdgpu-dwarf-line-number-information`.

AMDGPU does not use the ``isa`` state machine registers and always sets it to 0.
The instruction set must be obtained from the ELF file header ``e_flags`` field
in the ``EF_AMDGPU_MACH`` bit position (see :ref:`ELF Header
`). See DWARF Version 5 section 6.2.2.

.. TODO::

Should the ``isa`` state machine register be used to indicate if the code is
in wavefront32 or wavefront64 mode? Or used to specify the architecture ISA?

For AMDGPU the line number program header fields have the following values (see
DWARF Version 5 section 6.2.4):

``address_size`` (ubyte)
Matches the address size for the ``Global`` address space defined in
:ref:`amdgpu-dwarf-address-space-identifier`.

``segment_selector_size`` (ubyte)
AMDGPU does not use a segment selector so this is 0.

``minimum_instruction_length`` (ubyte)
For GFX9-GFX10 this is 4.

``maximum_operations_per_instruction`` (ubyte)
For GFX9-GFX10 this is 1.

Source text for online-compiled programs (for example, those compiled by the
OpenCL language runtime) may be embedded into the DWARF Version 5 line table.
See DWARF Version 5 section 6.2.4.1 which is updated by *DWARF Extensions For
Heterogeneous Debugging* section :ref:`DW_LNCT_LLVM_source
`.

The Clang option used to control source embedding in AMDGPU is defined in
:ref:`amdgpu-clang-debug-options-table`.

.. table:: AMDGPU Clang Debug Options
:name: amdgpu-clang-debug-options-table

==================== ==================================================
Debug Flag Description
==================== ==================================================
-g[no-]embed-source Enable/disable embedding source text in DWARF
debug sections. Useful for environments where
source cannot be written to disk, such as
when performing online compilation.
==================== ==================================================

For example:

``-gembed-source``
Enable the embedded source.

``-gno-embed-source``
Disable the embedded source.

32-Bit and 64-Bit DWARF Formats
-------------------------------

See DWARF Version 5 section 7.4 and
:ref:`amdgpu-dwarf-32-bit-and-64-bit-dwarf-formats`.

For AMDGPU:

* For the ``amdgcn`` target architecture only the 64-bit process address space
is supported.

* The producer can generate either 32-bit or 64-bit DWARF format. LLVM generates
the 32-bit DWARF format.

Unit Headers
------------

For AMDGPU the following values apply for each of the unit headers described in
DWARF Version 5 sections 7.5.1.1, 7.5.1.2, and 7.5.1.3:

``address_size`` (ubyte)
Matches the address size for the ``Global`` address space defined in
:ref:`amdgpu-dwarf-address-space-identifier`.

.. _amdgpu-code-conventions:

Code Conventions
================

This section provides code conventions used for each supported target triple OS
(see :ref:`amdgpu-target-triples`).

AMDHSA
------

This section provides code conventions used when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`).

.. _amdgpu-amdhsa-code-object-target-identification:

Code Object Target Identification
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The AMDHSA OS uses the following syntax to specify the code object
target as a single string:

``----``

Where:

- ````, ````, ```` and ````
are the same as the *Target Triple* (see
:ref:`amdgpu-target-triples`).

- ```` is the same as the *Processor* (see
:ref:`amdgpu-processors`).

- ```` is a list of the enabled *Target Features*
(see :ref:`amdgpu-target-features`), each prefixed by a plus, that
apply to *Processor*. The list must be in the same order as listed
in the table :ref:`amdgpu-target-feature-table`. Note that *Target
Features* must be included in the list if they are enabled even if
that is the default for *Processor*.

For example:

``"amdgcn-amd-amdhsa--gfx902+xnack"``

.. _amdgpu-amdhsa-code-object-metadata:

Code Object Metadata
~~~~~~~~~~~~~~~~~~~~

The code object metadata specifies extensible metadata associated with the code
objects executed on HSA [HSA]_ compatible runtimes such as AMD's ROCm
[AMD-ROCm]_. The encoding and semantics of this metadata depends on the code
object version; see :ref:`amdgpu-amdhsa-code-object-metadata-v2` and
:ref:`amdgpu-amdhsa-code-object-metadata-v3`.

Code object metadata is specified in a note record (see
:ref:`amdgpu-note-records`) and is required when the target triple OS is
``amdhsa`` (see :ref:`amdgpu-target-triples`). It must contain the minimum
information necessary to support the ROCM kernel queries. For example, the
segment sizes needed in a dispatch packet. In addition, a high-level language
runtime may require other information to be included. For example, the AMD
OpenCL runtime records kernel argument information.

.. _amdgpu-amdhsa-code-object-metadata-v2:

Code Object V2 Metadata (-mattr=-code-object-v3)
++++++++++++++++++++++++++++++++++++++++++++++++

.. warning:: Code Object V2 is not the default code object version emitted by
this version of LLVM. For a description of the metadata generated with the
default configuration (Code Object V3) see
:ref:`amdgpu-amdhsa-code-object-metadata-v3`.

Code object V2 metadata is specified by the ``NT_AMD_AMDGPU_METADATA`` note
record (see :ref:`amdgpu-note-records-v2`).

The metadata is specified as a YAML formatted string (see [YAML]_ and
:doc:`YamlIO`).

.. TODO::

Is the string null terminated? It probably should not if YAML allows it to
contain null characters, otherwise it should be.

The metadata is represented as a single YAML document comprised of the mapping
defined in table :ref:`amdgpu-amdhsa-code-object-metadata-map-table-v2` and
referenced tables.

For boolean values, the string values of ``false`` and ``true`` are used for
false and true respectively.

Additional information can be added to the mappings. To avoid conflicts, any
non-AMD key names should be prefixed by "*vendor-name*.".

.. table:: AMDHSA Code Object V2 Metadata Map
:name: amdgpu-amdhsa-code-object-metadata-map-table-v2

========== ============== ========= =======================================
String Key Value Type Required? Description
========== ============== ========= =======================================
"Version" sequence of Required - The first integer is the major
2 integers version. Currently 1.
- The second integer is the minor
version. Currently 0.
"Printf" sequence of Each string is encoded information
strings about a printf function call. The
encoded information is organized as
fields separated by colon (':'):

``ID:N:S[0]:S[1]:...:S[N-1]:FormatString``

where:

``ID``
A 32-bit integer as a unique id for
each printf function call

``N``
A 32-bit integer equal to the number
of arguments of printf function call
minus 1

``S[i]`` (where i = 0, 1, ... , N-1)
32-bit integers for the size in bytes
of the i-th FormatString argument of
the printf function call

FormatString
The format string passed to the
printf function call.
"Kernels" sequence of Required Sequence of the mappings for each
mapping kernel in the code object. See
:ref:`amdgpu-amdhsa-code-object-kernel-metadata-map-table-v2`
for the definition of the mapping.
========== ============== ========= =======================================

..

.. table:: AMDHSA Code Object V2 Kernel Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-metadata-map-table-v2

================= ============== ========= ================================
String Key Value Type Required? Description
================= ============== ========= ================================
"Name" string Required Source name of the kernel.
"SymbolName" string Required Name of the kernel
descriptor ELF symbol.
"Language" string Source language of the kernel.
Values include:

- "OpenCL C"
- "OpenCL C++"
- "HCC"
- "OpenMP"

"LanguageVersion" sequence of - The first integer is the major
2 integers version.
- The second integer is the
minor version.
"Attrs" mapping Mapping of kernel attributes.
See
:ref:`amdgpu-amdhsa-code-object-kernel-attribute-metadata-map-table-v2`
for the mapping definition.
"Args" sequence of Sequence of mappings of the
mapping kernel arguments. See
:ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v2`
for the definition of the mapping.
"CodeProps" mapping Mapping of properties related to
the kernel code. See
:ref:`amdgpu-amdhsa-code-object-kernel-code-properties-metadata-map-table-v2`
for the mapping definition.
================= ============== ========= ================================

..

.. table:: AMDHSA Code Object V2 Kernel Attribute Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-attribute-metadata-map-table-v2

=================== ============== ========= ==============================
String Key Value Type Required? Description
=================== ============== ========= ==============================
"ReqdWorkGroupSize" sequence of If not 0, 0, 0 then all values
3 integers must be >=1 and the dispatch
work-group size X, Y, Z must
correspond to the specified
values. Defaults to 0, 0, 0.

Corresponds to the OpenCL
``reqd_work_group_size``
attribute.
"WorkGroupSizeHint" sequence of The dispatch work-group size
3 integers X, Y, Z is likely to be the
specified values.

Corresponds to the OpenCL
``work_group_size_hint``
attribute.
"VecTypeHint" string The name of a scalar or vector
type.

Corresponds to the OpenCL
``vec_type_hint`` attribute.

"RuntimeHandle" string The external symbol name
associated with a kernel.
OpenCL runtime allocates a
global buffer for the symbol
and saves the kernel's address
to it, which is used for
device side enqueueing. Only
available for device side
enqueued kernels.
=================== ============== ========= ==============================

..

.. table:: AMDHSA Code Object V2 Kernel Argument Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v2

================= ============== ========= ================================
String Key Value Type Required? Description
================= ============== ========= ================================
"Name" string Kernel argument name.
"TypeName" string Kernel argument type name.
"Size" integer Required Kernel argument size in bytes.
"Align" integer Required Kernel argument alignment in
bytes. Must be a power of two.
"ValueKind" string Required Kernel argument kind that
specifies how to set up the
corresponding argument.
Values include:

"ByValue"
The argument is copied
directly into the kernarg.

"GlobalBuffer"
A global address space pointer
to the buffer data is passed
in the kernarg.

"DynamicSharedPointer"
A group address space pointer
to dynamically allocated LDS
is passed in the kernarg.

"Sampler"
A global address space
pointer to a S# is passed in
the kernarg.

"Image"
A global address space
pointer to a T# is passed in
the kernarg.

"Pipe"
A global address space pointer
to an OpenCL pipe is passed in
the kernarg.

"Queue"
A global address space pointer
to an OpenCL device enqueue
queue is passed in the
kernarg.

"HiddenGlobalOffsetX"
The OpenCL grid dispatch
global offset for the X
dimension is passed in the
kernarg.

"HiddenGlobalOffsetY"
The OpenCL grid dispatch
global offset for the Y
dimension is passed in the
kernarg.

"HiddenGlobalOffsetZ"
The OpenCL grid dispatch
global offset for the Z
dimension is passed in the
kernarg.

"HiddenNone"
An argument that is not used
by the kernel. Space needs to
be left for it, but it does
not need to be set up.

"HiddenPrintfBuffer"
A global address space pointer
to the runtime printf buffer
is passed in kernarg.

"HiddenHostcallBuffer"
A global address space pointer
to the runtime hostcall buffer
is passed in kernarg.

"HiddenDefaultQueue"
A global address space pointer
to the OpenCL device enqueue
queue that should be used by
the kernel by default is
passed in the kernarg.

"HiddenCompletionAction"
A global address space pointer
to help link enqueued kernels into
the ancestor tree for determining
when the parent kernel has finished.

"HiddenMultiGridSyncArg"
A global address space pointer for
multi-grid synchronization is
passed in the kernarg.

"ValueType" string Unused and deprecated. This should no longer
be emitted, but is accepted for compatibility.

"PointeeAlign" integer Alignment in bytes of pointee
type for pointer type kernel
argument. Must be a power
of 2. Only present if
"ValueKind" is
"DynamicSharedPointer".
"AddrSpaceQual" string Kernel argument address space
qualifier. Only present if
"ValueKind" is "GlobalBuffer" or
"DynamicSharedPointer". Values
are:

- "Private"
- "Global"
- "Constant"
- "Local"
- "Generic"
- "Region"

.. TODO::
Is GlobalBuffer only Global
or Constant? Is
DynamicSharedPointer always
Local? Can HCC allow Generic?
How can Private or Region
ever happen?
"AccQual" string Kernel argument access
qualifier. Only present if
"ValueKind" is "Image" or
"Pipe". Values
are:

- "ReadOnly"
- "WriteOnly"
- "ReadWrite"

.. TODO::
Does this apply to
GlobalBuffer?
"ActualAccQual" string The actual memory accesses
performed by the kernel on the
kernel argument. Only present if
"ValueKind" is "GlobalBuffer",
"Image", or "Pipe". This may be
more restrictive than indicated
by "AccQual" to reflect what the
kernel actual does. If not
present then the runtime must
assume what is implied by
"AccQual" and "IsConst". Values
are:

- "ReadOnly"
- "WriteOnly"
- "ReadWrite"

"IsConst" boolean Indicates if the kernel argument
is const qualified. Only present
if "ValueKind" is
"GlobalBuffer".

"IsRestrict" boolean Indicates if the kernel argument
is restrict qualified. Only
present if "ValueKind" is
"GlobalBuffer".

"IsVolatile" boolean Indicates if the kernel argument
is volatile qualified. Only
present if "ValueKind" is
"GlobalBuffer".

"IsPipe" boolean Indicates if the kernel argument
is pipe qualified. Only present
if "ValueKind" is "Pipe".

.. TODO::
Can GlobalBuffer be pipe
qualified?
================= ============== ========= ================================

..

.. table:: AMDHSA Code Object V2 Kernel Code Properties Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-code-properties-metadata-map-table-v2

============================ ============== ========= =====================
String Key Value Type Required? Description
============================ ============== ========= =====================
"KernargSegmentSize" integer Required The size in bytes of
the kernarg segment
that holds the values
of the arguments to
the kernel.
"GroupSegmentFixedSize" integer Required The amount of group
segment memory
required by a
work-group in
bytes. This does not
include any
dynamically allocated
group segment memory
that may be added
when the kernel is
dispatched.
"PrivateSegmentFixedSize" integer Required The amount of fixed
private address space
memory required for a
work-item in
bytes. If the kernel
uses a dynamic call
stack then additional
space must be added
to this value for the
call stack.
"KernargSegmentAlign" integer Required The maximum byte
alignment of
arguments in the
kernarg segment. Must
be a power of 2.
"WavefrontSize" integer Required Wavefront size. Must
be a power of 2.
"NumSGPRs" integer Required Number of scalar
registers used by a
wavefront for
GFX6-GFX10. This
includes the special
SGPRs for VCC, Flat
Scratch (GFX7-GFX10)
and XNACK (for
GFX8-GFX10). It does
not include the 16
SGPR added if a trap
handler is
enabled. It is not
rounded up to the
allocation
granularity.
"NumVGPRs" integer Required Number of vector
registers used by
each work-item for
GFX6-GFX10
"MaxFlatWorkGroupSize" integer Required Maximum flat
work-group size
supported by the
kernel in work-items.
Must be >=1 and
consistent with
ReqdWorkGroupSize if
not 0, 0, 0.
"NumSpilledSGPRs" integer Number of stores from
a scalar register to
a register allocator
created spill
location.
"NumSpilledVGPRs" integer Number of stores from
a vector register to
a register allocator
created spill
location.
============================ ============== ========= =====================

.. _amdgpu-amdhsa-code-object-metadata-v3:

Code Object V3 Metadata (-mattr=+code-object-v3)
++++++++++++++++++++++++++++++++++++++++++++++++

Code object V3 metadata is specified by the ``NT_AMDGPU_METADATA`` note record
(see :ref:`amdgpu-note-records-v3`).

The metadata is represented as Message Pack formatted binary data (see
[MsgPack]_). The top level is a Message Pack map that includes the
keys defined in table
:ref:`amdgpu-amdhsa-code-object-metadata-map-table-v3` and referenced
tables.

Additional information can be added to the maps. To avoid conflicts,
any key names should be prefixed by "*vendor-name*." where
``vendor-name`` can be the name of the vendor and specific vendor
tool that generates the information. The prefix is abbreviated to
simply "." when it appears within a map that has been added by the
same *vendor-name*.

.. table:: AMDHSA Code Object V3 Metadata Map
:name: amdgpu-amdhsa-code-object-metadata-map-table-v3

================= ============== ========= =======================================
String Key Value Type Required? Description
================= ============== ========= =======================================
"amdhsa.version" sequence of Required - The first integer is the major
2 integers version. Currently 1.
- The second integer is the minor
version. Currently 0.
"amdhsa.printf" sequence of Each string is encoded information
strings about a printf function call. The
encoded information is organized as
fields separated by colon (':'):

``ID:N:S[0]:S[1]:...:S[N-1]:FormatString``

where:

``ID``
A 32-bit integer as a unique id for
each printf function call

``N``
A 32-bit integer equal to the number
of arguments of printf function call
minus 1

``S[i]`` (where i = 0, 1, ... , N-1)
32-bit integers for the size in bytes
of the i-th FormatString argument of
the printf function call

FormatString
The format string passed to the
printf function call.
"amdhsa.kernels" sequence of Required Sequence of the maps for each
map kernel in the code object. See
:ref:`amdgpu-amdhsa-code-object-kernel-metadata-map-table-v3`
for the definition of the keys included
in that map.
================= ============== ========= =======================================

..

.. table:: AMDHSA Code Object V3 Kernel Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-metadata-map-table-v3

=================================== ============== ========= ================================
String Key Value Type Required? Description
=================================== ============== ========= ================================
".name" string Required Source name of the kernel.
".symbol" string Required Name of the kernel
descriptor ELF symbol.
".language" string Source language of the kernel.
Values include:

- "OpenCL C"
- "OpenCL C++"
- "HCC"
- "HIP"
- "OpenMP"
- "Assembler"

".language_version" sequence of - The first integer is the major
2 integers version.
- The second integer is the
minor version.
".args" sequence of Sequence of maps of the
map kernel arguments. See
:ref:`amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v3`
for the definition of the keys
included in that map.
".reqd_workgroup_size" sequence of If not 0, 0, 0 then all values
3 integers must be >=1 and the dispatch
work-group size X, Y, Z must
correspond to the specified
values. Defaults to 0, 0, 0.

Corresponds to the OpenCL
``reqd_work_group_size``
attribute.
".workgroup_size_hint" sequence of The dispatch work-group size
3 integers X, Y, Z is likely to be the
specified values.

Corresponds to the OpenCL
``work_group_size_hint``
attribute.
".vec_type_hint" string The name of a scalar or vector
type.

Corresponds to the OpenCL
``vec_type_hint`` attribute.

".device_enqueue_symbol" string The external symbol name
associated with a kernel.
OpenCL runtime allocates a
global buffer for the symbol
and saves the kernel's address
to it, which is used for
device side enqueueing. Only
available for device side
enqueued kernels.
".kernarg_segment_size" integer Required The size in bytes of
the kernarg segment
that holds the values
of the arguments to
the kernel.
".group_segment_fixed_size" integer Required The amount of group
segment memory
required by a
work-group in
bytes. This does not
include any
dynamically allocated
group segment memory
that may be added
when the kernel is
dispatched.
".private_segment_fixed_size" integer Required The amount of fixed
private address space
memory required for a
work-item in
bytes. If the kernel
uses a dynamic call
stack then additional
space must be added
to this value for the
call stack.
".kernarg_segment_align" integer Required The maximum byte
alignment of
arguments in the
kernarg segment. Must
be a power of 2.
".wavefront_size" integer Required Wavefront size. Must
be a power of 2.
".sgpr_count" integer Required Number of scalar
registers required by a
wavefront for
GFX6-GFX9. A register
is required if it is
used explicitly, or
if a higher numbered
register is used
explicitly. This
includes the special
SGPRs for VCC, Flat
Scratch (GFX7-GFX9)
and XNACK (for
GFX8-GFX9). It does
not include the 16
SGPR added if a trap
handler is
enabled. It is not
rounded up to the
allocation
granularity.
".vgpr_count" integer Required Number of vector
registers required by
each work-item for
GFX6-GFX9. A register
is required if it is
used explicitly, or
if a higher numbered
register is used
explicitly.
".max_flat_workgroup_size" integer Required Maximum flat
work-group size
supported by the
kernel in work-items.
Must be >=1 and
consistent with
ReqdWorkGroupSize if
not 0, 0, 0.
".sgpr_spill_count" integer Number of stores from
a scalar register to
a register allocator
created spill
location.
".vgpr_spill_count" integer Number of stores from
a vector register to
a register allocator
created spill
location.
=================================== ============== ========= ================================

..

.. table:: AMDHSA Code Object V3 Kernel Argument Metadata Map
:name: amdgpu-amdhsa-code-object-kernel-argument-metadata-map-table-v3

====================== ============== ========= ================================
String Key Value Type Required? Description
====================== ============== ========= ================================
".name" string Kernel argument name.
".type_name" string Kernel argument type name.
".size" integer Required Kernel argument size in bytes.
".offset" integer Required Kernel argument offset in
bytes. The offset must be a
multiple of the alignment
required by the argument.
".value_kind" string Required Kernel argument kind that
specifies how to set up the
corresponding argument.
Values include:

"by_value"
The argument is copied
directly into the kernarg.

"global_buffer"
A global address space pointer
to the buffer data is passed
in the kernarg.

"dynamic_shared_pointer"
A group address space pointer
to dynamically allocated LDS
is passed in the kernarg.

"sampler"
A global address space
pointer to a S# is passed in
the kernarg.

"image"
A global address space
pointer to a T# is passed in
the kernarg.

"pipe"
A global address space pointer
to an OpenCL pipe is passed in
the kernarg.

"queue"
A global address space pointer
to an OpenCL device enqueue
queue is passed in the
kernarg.

"hidden_global_offset_x"
The OpenCL grid dispatch
global offset for the X
dimension is passed in the
kernarg.

"hidden_global_offset_y"
The OpenCL grid dispatch
global offset for the Y
dimension is passed in the
kernarg.

"hidden_global_offset_z"
The OpenCL grid dispatch
global offset for the Z
dimension is passed in the
kernarg.

"hidden_none"
An argument that is not used
by the kernel. Space needs to
be left for it, but it does
not need to be set up.

"hidden_printf_buffer"
A global address space pointer
to the runtime printf buffer
is passed in kernarg.

"hidden_hostcall_buffer"
A global address space pointer
to the runtime hostcall buffer
is passed in kernarg.

"hidden_default_queue"
A global address space pointer
to the OpenCL device enqueue
queue that should be used by
the kernel by default is
passed in the kernarg.

"hidden_completion_action"
A global address space pointer
to help link enqueued kernels into
the ancestor tree for determining
when the parent kernel has finished.

"hidden_multigrid_sync_arg"
A global address space pointer for
multi-grid synchronization is
passed in the kernarg.

".value_type" string Unused and deprecated. This should no longer
be emitted, but is accepted for compatibility.

".pointee_align" integer Alignment in bytes of pointee
type for pointer type kernel
argument. Must be a power
of 2. Only present if
".value_kind" is
"dynamic_shared_pointer".
".address_space" string Kernel argument address space
qualifier. Only present if
".value_kind" is "global_buffer" or
"dynamic_shared_pointer". Values
are:

- "private"
- "global"
- "constant"
- "local"
- "generic"
- "region"

.. TODO::
Is "global_buffer" only "global"
or "constant"? Is
"dynamic_shared_pointer" always
"local"? Can HCC allow "generic"?
How can "private" or "region"
ever happen?
".access" string Kernel argument access
qualifier. Only present if
".value_kind" is "image" or
"pipe". Values
are:

- "read_only"
- "write_only"
- "read_write"

.. TODO::
Does this apply to
"global_buffer"?
".actual_access" string The actual memory accesses
performed by the kernel on the
kernel argument. Only present if
".value_kind" is "global_buffer",
"image", or "pipe". This may be
more restrictive than indicated
by ".access" to reflect what the
kernel actual does. If not
present then the runtime must
assume what is implied by
".access" and ".is_const" . Values
are:

- "read_only"
- "write_only"
- "read_write"

".is_const" boolean Indicates if the kernel argument
is const qualified. Only present
if ".value_kind" is
"global_buffer".

".is_restrict" boolean Indicates if the kernel argument
is restrict qualified. Only
present if ".value_kind" is
"global_buffer".

".is_volatile" boolean Indicates if the kernel argument
is volatile qualified. Only
present if ".value_kind" is
"global_buffer".

".is_pipe" boolean Indicates if the kernel argument
is pipe qualified. Only present
if ".value_kind" is "pipe".

.. TODO::
Can "global_buffer" be pipe
qualified?
====================== ============== ========= ================================

..

Kernel Dispatch
~~~~~~~~~~~~~~~

The HSA architected queuing language (AQL) defines a user space memory
interface that can be used to control the dispatch of kernels, in an agent
independent way. An agent can have zero or more AQL queues created for it using
the ROCm runtime, in which AQL packets (all of which are 64 bytes) can be
placed. See the *HSA Platform System Architecture Specification* [HSA]_ for the
AQL queue mechanics and packet layouts.

The packet processor of a kernel agent is responsible for detecting and
dispatching HSA kernels from the AQL queues associated with it. For AMD GPUs the
packet processor is implemented by the hardware command processor (CP),
asynchronous dispatch controller (ADC) and shader processor input controller
(SPI).

The ROCm runtime can be used to allocate an AQL queue object. It uses the kernel
mode driver to initialize and register the AQL queue with CP.

To dispatch a kernel the following actions are performed. This can occur in the
CPU host program, or from an HSA kernel executing on a GPU.

1. A pointer to an AQL queue for the kernel agent on which the kernel is to be
executed is obtained.
2. A pointer to the kernel descriptor (see
:ref:`amdgpu-amdhsa-kernel-descriptor`) of the kernel to execute is obtained.
It must be for a kernel that is contained in a code object that that was
loaded by the ROCm runtime on the kernel agent with which the AQL queue is
associated.
3. Space is allocated for the kernel arguments using the ROCm runtime allocator
for a memory region with the kernarg property for the kernel agent that will
execute the kernel. It must be at least 16-byte aligned.
4. Kernel argument values are assigned to the kernel argument memory
allocation. The layout is defined in the *HSA Programmer's Language
Reference* [HSA]_. For AMDGPU the kernel execution directly accesses the
kernel argument memory in the same way constant memory is accessed. (Note
that the HSA specification allows an implementation to copy the kernel
argument contents to another location that is accessed by the kernel.)
5. An AQL kernel dispatch packet is created on the AQL queue. The ROCm runtime
api uses 64-bit atomic operations to reserve space in the AQL queue for the
packet. The packet must be set up, and the final write must use an atomic
store release to set the packet kind to ensure the packet contents are
visible to the kernel agent. AQL defines a doorbell signal mechanism to
notify the kernel agent that the AQL queue has been updated. These rules, and
the layout of the AQL queue and kernel dispatch packet is defined in the *HSA
System Architecture Specification* [HSA]_.
6. A kernel dispatch packet includes information about the actual dispatch,
such as grid and work-group size, together with information from the code
object about the kernel, such as segment sizes. The ROCm runtime queries on
the kernel symbol can be used to obtain the code object values which are
recorded in the :ref:`amdgpu-amdhsa-code-object-metadata`.
7. CP executes micro-code and is responsible for detecting and setting up the
GPU to execute the wavefronts of a kernel dispatch.
8. CP ensures that when the a wavefront starts executing the kernel machine
code, the scalar general purpose registers (SGPR) and vector general purpose
registers (VGPR) are set up as required by the machine code. The required
setup is defined in the :ref:`amdgpu-amdhsa-kernel-descriptor`. The initial
register state is defined in
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`.
9. The prolog of the kernel machine code (see
:ref:`amdgpu-amdhsa-kernel-prolog`) sets up the machine state as necessary
before continuing executing the machine code that corresponds to the kernel.
10. When the kernel dispatch has completed execution, CP signals the completion
signal specified in the kernel dispatch packet if not 0.

Image and Samplers
~~~~~~~~~~~~~~~~~~

Image and sample handles created by the ROCm runtime are 64-bit addresses of a
hardware 32-byte V# and 48 byte S# object respectively. In order to support the
HSA ``query_sampler`` operations two extra dwords are used to store the HSA BRIG
enumeration values for the queries that are not trivially deducible from the S#
representation.

HSA Signals
~~~~~~~~~~~

HSA signal handles created by the ROCm runtime are 64-bit addresses of a
structure allocated in memory accessible from both the CPU and GPU. The
structure is defined by the ROCm runtime and subject to change between releases
(see [AMD-ROCm-github]_).

.. _amdgpu-amdhsa-hsa-aql-queue:

HSA AQL Queue
~~~~~~~~~~~~~

The HSA AQL queue structure is defined by the ROCm runtime and subject to change
between releases (see [AMD-ROCm-github]_). For some processors it contains
fields needed to implement certain language features such as the flat address
aperture bases. It also contains fields used by CP such as managing the
allocation of scratch memory.

.. _amdgpu-amdhsa-kernel-descriptor:

Kernel Descriptor
~~~~~~~~~~~~~~~~~

A kernel descriptor consists of the information needed by CP to initiate the
execution of a kernel, including the entry point address of the machine code
that implements the kernel.

Kernel Descriptor for GFX6-GFX10
++++++++++++++++++++++++++++++++

CP microcode requires the Kernel descriptor to be allocated on 64-byte
alignment.

.. table:: Kernel Descriptor for GFX6-GFX10
:name: amdgpu-amdhsa-kernel-descriptor-gfx6-gfx10-table

======= ======= =============================== ============================
Bits Size Field Name Description
======= ======= =============================== ============================
31:0 4 bytes GROUP_SEGMENT_FIXED_SIZE The amount of fixed local
address space memory
required for a work-group
in bytes. This does not
include any dynamically
allocated local address
space memory that may be
added when the kernel is
dispatched.
63:32 4 bytes PRIVATE_SEGMENT_FIXED_SIZE The amount of fixed
private address space
memory required for a
work-item in bytes. If
is_dynamic_callstack is 1
then additional space must
be added to this value for
the call stack.
127:64 8 bytes Reserved, must be 0.
191:128 8 bytes KERNEL_CODE_ENTRY_BYTE_OFFSET Byte offset (possibly
negative) from base
address of kernel
descriptor to kernel's
entry point instruction
which must be 256 byte
aligned.
351:272 20 Reserved, must be 0.
bytes
383:352 4 bytes COMPUTE_PGM_RSRC3 GFX6-9
Reserved, must be 0.
GFX10
Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC3``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc3-gfx10-table`.
415:384 4 bytes COMPUTE_PGM_RSRC1 Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC1``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table`.
447:416 4 bytes COMPUTE_PGM_RSRC2 Compute Shader (CS)
program settings used by
CP to set up
``COMPUTE_PGM_RSRC2``
configuration
register. See
:ref:`amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table`.
448 1 bit ENABLE_SGPR_PRIVATE_SEGMENT Enable the setup of the
_BUFFER SGPR user data registers
(see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

The total number of SGPR
user data registers
requested must not exceed
16 and match value in
``compute_pgm_rsrc2.user_sgpr.user_sgpr_count``.
Any requests beyond 16
will be ignored.
449 1 bit ENABLE_SGPR_DISPATCH_PTR *see above*
450 1 bit ENABLE_SGPR_QUEUE_PTR *see above*
451 1 bit ENABLE_SGPR_KERNARG_SEGMENT_PTR *see above*
452 1 bit ENABLE_SGPR_DISPATCH_ID *see above*
453 1 bit ENABLE_SGPR_FLAT_SCRATCH_INIT *see above*
454 1 bit ENABLE_SGPR_PRIVATE_SEGMENT *see above*
_SIZE
457:455 3 bits Reserved, must be 0.
458 1 bit ENABLE_WAVEFRONT_SIZE32 GFX6-9
Reserved, must be 0.
GFX10
- If 0 execute in
wavefront size 64 mode.
- If 1 execute in
native wavefront size
32 mode.
463:459 5 bits Reserved, must be 0.
511:464 6 bytes Reserved, must be 0.
512 **Total size 64 bytes.**
======= ====================================================================

..

.. table:: compute_pgm_rsrc1 for GFX6-GFX10
:name: amdgpu-amdhsa-compute_pgm_rsrc1-gfx6-gfx10-table

======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
5:0 6 bits GRANULATED_WORKITEM_VGPR_COUNT Number of vector register
blocks used by each work-item;
granularity is device
specific:

GFX6-GFX9
- vgprs_used 0..256
- max(0, ceil(vgprs_used / 4) - 1)
GFX10 (wavefront size 64)
- max_vgpr 1..256
- max(0, ceil(vgprs_used / 4) - 1)
GFX10 (wavefront size 32)
- max_vgpr 1..256
- max(0, ceil(vgprs_used / 8) - 1)

Where vgprs_used is defined
as the highest VGPR number
explicitly referenced plus
one.

Used by CP to set up
``COMPUTE_PGM_RSRC1.VGPRS``.

The
:ref:`amdgpu-assembler`
calculates this
automatically for the
selected processor from
values provided to the
`.amdhsa_kernel` directive
by the
`.amdhsa_next_free_vgpr`
nested directive (see
:ref:`amdhsa-kernel-directives-table`).
9:6 4 bits GRANULATED_WAVEFRONT_SGPR_COUNT Number of scalar register
blocks used by a wavefront;
granularity is device
specific:

GFX6-GFX8
- sgprs_used 0..112
- max(0, ceil(sgprs_used / 8) - 1)
GFX9
- sgprs_used 0..112
- 2 * max(0, ceil(sgprs_used / 16) - 1)
GFX10
Reserved, must be 0.
(128 SGPRs always
allocated.)

Where sgprs_used is
defined as the highest
SGPR number explicitly
referenced plus one, plus
a target specific number
of additional special
SGPRs for VCC,
FLAT_SCRATCH (GFX7+) and
XNACK_MASK (GFX8+), and
any additional
target specific
limitations. It does not
include the 16 SGPRs added
if a trap handler is
enabled.

The target specific
limitations and special
SGPR layout are defined in
the hardware
documentation, which can
be found in the
:ref:`amdgpu-processors`
table.

Used by CP to set up
``COMPUTE_PGM_RSRC1.SGPRS``.

The
:ref:`amdgpu-assembler`
calculates this
automatically for the
selected processor from
values provided to the
`.amdhsa_kernel` directive
by the
`.amdhsa_next_free_sgpr`
and `.amdhsa_reserve_*`
nested directives (see
:ref:`amdhsa-kernel-directives-table`).
11:10 2 bits PRIORITY Must be 0.

Start executing wavefront
at the specified priority.

CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.PRIORITY``.
13:12 2 bits FLOAT_ROUND_MODE_32 Wavefront starts execution
with specified rounding
mode for single (32
bit) floating point
precision floating point
operations.

Floating point rounding
mode values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.

Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
15:14 2 bits FLOAT_ROUND_MODE_16_64 Wavefront starts execution
with specified rounding
denorm mode for half/double (16
and 64-bit) floating point
precision floating point
operations.

Floating point rounding
mode values are defined in
:ref:`amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table`.

Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
17:16 2 bits FLOAT_DENORM_MODE_32 Wavefront starts execution
with specified denorm mode
for single (32
bit) floating point
precision floating point
operations.

Floating point denorm mode
values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.

Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
19:18 2 bits FLOAT_DENORM_MODE_16_64 Wavefront starts execution
with specified denorm mode
for half/double (16
and 64-bit) floating point
precision floating point
operations.

Floating point denorm mode
values are defined in
:ref:`amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table`.

Used by CP to set up
``COMPUTE_PGM_RSRC1.FLOAT_MODE``.
20 1 bit PRIV Must be 0.

Start executing wavefront
in privilege trap handler
mode.

CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.PRIV``.
21 1 bit ENABLE_DX10_CLAMP Wavefront starts execution
with DX10 clamp mode
enabled. Used by the vector
ALU to force DX10 style
treatment of NaN's (when
set, clamp NaN to zero,
otherwise pass NaN
through).

Used by CP to set up
``COMPUTE_PGM_RSRC1.DX10_CLAMP``.
22 1 bit DEBUG_MODE Must be 0.

Start executing wavefront
in single step mode.

CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.DEBUG_MODE``.
23 1 bit ENABLE_IEEE_MODE Wavefront starts execution
with IEEE mode
enabled. Floating point
opcodes that support
exception flag gathering
will quiet and propagate
signaling-NaN inputs per
IEEE 754-2008. Min_dx10 and
max_dx10 become IEEE
754-2008 compliant due to
signaling-NaN propagation
and quieting.

Used by CP to set up
``COMPUTE_PGM_RSRC1.IEEE_MODE``.
24 1 bit BULKY Must be 0.

Only one work-group allowed
to execute on a compute
unit.

CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.BULKY``.
25 1 bit CDBG_USER Must be 0.

Flag that can be used to
control debugging code.

CP is responsible for
filling in
``COMPUTE_PGM_RSRC1.CDBG_USER``.
26 1 bit FP16_OVFL GFX6-GFX8
Reserved, must be 0.
GFX9-GFX10
Wavefront starts execution
with specified fp16 overflow
mode.

- If 0, fp16 overflow generates
+/-INF values.
- If 1, fp16 overflow that is the
result of an +/-INF input value
or divide by 0 produces a +/-INF,
otherwise clamps computed
overflow to +/-MAX_FP16 as
appropriate.

Used by CP to set up
``COMPUTE_PGM_RSRC1.FP16_OVFL``.
28:27 2 bits Reserved, must be 0.
29 1 bit WGP_MODE GFX6-GFX9
Reserved, must be 0.
GFX10
- If 0 execute work-groups in
CU wavefront execution mode.
- If 1 execute work-groups on
in WGP wavefront execution mode.

See :ref:`amdgpu-amdhsa-memory-model`.

Used by CP to set up
``COMPUTE_PGM_RSRC1.WGP_MODE``.
30 1 bit MEM_ORDERED GFX6-9
Reserved, must be 0.
GFX10
Controls the behavior of the
waitcnt's vmcnt and vscnt
counters.

- If 0 vmcnt reports completion
of load and atomic with return
out of order with sample
instructions, and the vscnt
reports the completion of
store and atomic without
return in order.
- If 1 vmcnt reports completion
of load, atomic with return
and sample instructions in
order, and the vscnt reports
the completion of store and
atomic without return in order.

Used by CP to set up
``COMPUTE_PGM_RSRC1.MEM_ORDERED``.
31 1 bit FWD_PROGRESS GFX6-9
Reserved, must be 0.
GFX10
- If 0 execute SIMD wavefronts
using oldest first policy.
- If 1 execute SIMD wavefronts to
ensure wavefronts will make some
forward progress.

Used by CP to set up
``COMPUTE_PGM_RSRC1.FWD_PROGRESS``.
32 **Total size 4 bytes**
======= ===================================================================================================================

..

.. table:: compute_pgm_rsrc2 for GFX6-GFX10
:name: amdgpu-amdhsa-compute_pgm_rsrc2-gfx6-gfx10-table

======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
0 1 bit ENABLE_SGPR_PRIVATE_SEGMENT Enable the setup of the
_WAVEFRONT_OFFSET SGPR wavefront scratch offset
system register (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

Used by CP to set up
``COMPUTE_PGM_RSRC2.SCRATCH_EN``.
5:1 5 bits USER_SGPR_COUNT The total number of SGPR
user data registers
requested. This number must
match the number of user
data registers enabled.

Used by CP to set up
``COMPUTE_PGM_RSRC2.USER_SGPR``.
6 1 bit ENABLE_TRAP_HANDLER Must be 0.

This bit represents
``COMPUTE_PGM_RSRC2.TRAP_PRESENT``,
which is set by the CP if
the runtime has installed a
trap handler.
7 1 bit ENABLE_SGPR_WORKGROUP_ID_X Enable the setup of the
system SGPR register for
the work-group id in the X
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_X_EN``.
8 1 bit ENABLE_SGPR_WORKGROUP_ID_Y Enable the setup of the
system SGPR register for
the work-group id in the Y
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_Y_EN``.
9 1 bit ENABLE_SGPR_WORKGROUP_ID_Z Enable the setup of the
system SGPR register for
the work-group id in the Z
dimension (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_Z_EN``.
10 1 bit ENABLE_SGPR_WORKGROUP_INFO Enable the setup of the
system SGPR register for
work-group information (see
:ref:`amdgpu-amdhsa-initial-kernel-execution-state`).

Used by CP to set up
``COMPUTE_PGM_RSRC2.TGID_SIZE_EN``.
12:11 2 bits ENABLE_VGPR_WORKITEM_ID Enable the setup of the
VGPR system registers used
for the work-item ID.
:ref:`amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table`
defines the values.

Used by CP to set up
``COMPUTE_PGM_RSRC2.TIDIG_CMP_CNT``.
13 1 bit ENABLE_EXCEPTION_ADDRESS_WATCH Must be 0.

Wavefront starts execution
with address watch
exceptions enabled which
are generated when L1 has
witnessed a thread access
an *address of
interest*.

CP is responsible for
filling in the address
watch bit in
``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
according to what the
runtime requests.
14 1 bit ENABLE_EXCEPTION_MEMORY Must be 0.

Wavefront starts execution
with memory violation
exceptions exceptions
enabled which are generated
when a memory violation has
occurred for this wavefront from
L1 or LDS
(write-to-read-only-memory,
mis-aligned atomic, LDS
address out of range,
illegal address, etc.).

CP sets the memory
violation bit in
``COMPUTE_PGM_RSRC2.EXCP_EN_MSB``
according to what the
runtime requests.
23:15 9 bits GRANULATED_LDS_SIZE Must be 0.

CP uses the rounded value
from the dispatch packet,
not this value, as the
dispatch may contain
dynamically allocated group
segment memory. CP writes
directly to
``COMPUTE_PGM_RSRC2.LDS_SIZE``.

Amount of group segment
(LDS) to allocate for each
work-group. Granularity is
device specific:

GFX6:
roundup(lds-size / (64 * 4))
GFX7-GFX10:
roundup(lds-size / (128 * 4))

24 1 bit ENABLE_EXCEPTION_IEEE_754_FP Wavefront starts execution
_INVALID_OPERATION with specified exceptions
enabled.

Used by CP to set up
``COMPUTE_PGM_RSRC2.EXCP_EN``
(set from bits 0..6).

IEEE 754 FP Invalid
Operation
25 1 bit ENABLE_EXCEPTION_FP_DENORMAL FP Denormal one or more
_SOURCE input operands is a
denormal number
26 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Division by
_DIVISION_BY_ZERO Zero
27 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP FP Overflow
_OVERFLOW
28 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Underflow
_UNDERFLOW
29 1 bit ENABLE_EXCEPTION_IEEE_754_FP IEEE 754 FP Inexact
_INEXACT
30 1 bit ENABLE_EXCEPTION_INT_DIVIDE_BY Integer Division by Zero
_ZERO (rcp_iflag_f32 instruction
only)
31 1 bit Reserved, must be 0.
32 **Total size 4 bytes.**
======= ===================================================================================================================

..

.. table:: compute_pgm_rsrc3 for GFX10
:name: amdgpu-amdhsa-compute_pgm_rsrc3-gfx10-table

======= ======= =============================== ===========================================================================
Bits Size Field Name Description
======= ======= =============================== ===========================================================================
3:0 4 bits SHARED_VGPR_COUNT Number of shared VGPRs for wavefront size 64. Granularity 8. Value 0-120.
compute_pgm_rsrc1.vgprs + shared_vgpr_cnt cannot exceed 64.
31:4 28 Reserved, must be 0.
bits
32 **Total size 4 bytes.**
======= ===================================================================================================================

..

.. table:: Floating Point Rounding Mode Enumeration Values
:name: amdgpu-amdhsa-floating-point-rounding-mode-enumeration-values-table

====================================== ===== ==============================
Enumeration Name Value Description
====================================== ===== ==============================
FLOAT_ROUND_MODE_NEAR_EVEN 0 Round Ties To Even
FLOAT_ROUND_MODE_PLUS_INFINITY 1 Round Toward +infinity
FLOAT_ROUND_MODE_MINUS_INFINITY 2 Round Toward -infinity
FLOAT_ROUND_MODE_ZERO 3 Round Toward 0
====================================== ===== ==============================

..

.. table:: Floating Point Denorm Mode Enumeration Values
:name: amdgpu-amdhsa-floating-point-denorm-mode-enumeration-values-table

====================================== ===== ==============================
Enumeration Name Value Description
====================================== ===== ==============================
FLOAT_DENORM_MODE_FLUSH_SRC_DST 0 Flush Source and Destination
Denorms
FLOAT_DENORM_MODE_FLUSH_DST 1 Flush Output Denorms
FLOAT_DENORM_MODE_FLUSH_SRC 2 Flush Source Denorms
FLOAT_DENORM_MODE_FLUSH_NONE 3 No Flush
====================================== ===== ==============================

..

.. table:: System VGPR Work-Item ID Enumeration Values
:name: amdgpu-amdhsa-system-vgpr-work-item-id-enumeration-values-table

======================================== ===== ============================
Enumeration Name Value Description
======================================== ===== ============================
SYSTEM_VGPR_WORKITEM_ID_X 0 Set work-item X dimension
ID.
SYSTEM_VGPR_WORKITEM_ID_X_Y 1 Set work-item X and Y
dimensions ID.
SYSTEM_VGPR_WORKITEM_ID_X_Y_Z 2 Set work-item X, Y and Z
dimensions ID.
SYSTEM_VGPR_WORKITEM_ID_UNDEFINED 3 Undefined.
======================================== ===== ============================

.. _amdgpu-amdhsa-initial-kernel-execution-state:

Initial Kernel Execution State
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This section defines the register state that will be set up by the packet
processor prior to the start of execution of every wavefront. This is limited by
the constraints of the hardware controllers of CP/ADC/SPI.

The order of the SGPR registers is defined, but the compiler can specify which
ones are actually setup in the kernel descriptor using the ``enable_sgpr_*`` bit
fields (see :ref:`amdgpu-amdhsa-kernel-descriptor`). The register numbers used
for enabled registers are dense starting at SGPR0: the first enabled register is
SGPR0, the next enabled register is SGPR1 etc.; disabled registers do not have
an SGPR number.

The initial SGPRs comprise up to 16 User SRGPs that are set by CP and apply to
all wavefronts of the grid. It is possible to specify more than 16 User SGPRs
using the ``enable_sgpr_*`` bit fields, in which case only the first 16 are
actually initialized. These are then immediately followed by the System SGPRs
that are set up by ADC/SPI and can have different values for each wavefront of
the grid dispatch.

SGPR register initial state is defined in
:ref:`amdgpu-amdhsa-sgpr-register-set-up-order-table`.

.. table:: SGPR Register Set Up Order
:name: amdgpu-amdhsa-sgpr-register-set-up-order-table

========== ========================== ====== ==============================
SGPR Order Name Number Description
(kernel descriptor enable of
field) SGPRs
========== ========================== ====== ==============================
First Private Segment Buffer 4 V# that can be used, together
(enable_sgpr_private with Scratch Wavefront Offset
_segment_buffer) as an offset, to access the
private address space using a
segment address.

CP uses the value provided by
the runtime.
then Dispatch Ptr 2 64-bit address of AQL dispatch
(enable_sgpr_dispatch_ptr) packet for kernel dispatch
actually executing.
then Queue Ptr 2 64-bit address of amd_queue_t
(enable_sgpr_queue_ptr) object for AQL queue on which
the dispatch packet was
queued.
then Kernarg Segment Ptr 2 64-bit address of Kernarg
(enable_sgpr_kernarg segment. This is directly
_segment_ptr) copied from the
kernarg_address in the kernel
dispatch packet.

Having CP load it once avoids
loading it at the beginning of
every wavefront.
then Dispatch Id 2 64-bit Dispatch ID of the
(enable_sgpr_dispatch_id) dispatch packet being
executed.
then Flat Scratch Init 2 This is 2 SGPRs:
(enable_sgpr_flat_scratch
_init) GFX6
Not supported.
GFX7-GFX8
The first SGPR is a 32-bit
byte offset from
``SH_HIDDEN_PRIVATE_BASE_VIMID``
to per SPI base of memory
for scratch for the queue
executing the kernel
dispatch. CP obtains this
from the runtime. (The
Scratch Segment Buffer base
address is
``SH_HIDDEN_PRIVATE_BASE_VIMID``
plus this offset.) The value
of Scratch Wavefront Offset must
be added to this offset by
the kernel machine code,
right shifted by 8, and
moved to the FLAT_SCRATCH_HI
SGPR register.
FLAT_SCRATCH_HI corresponds
to SGPRn-4 on GFX7, and
SGPRn-6 on GFX8 (where SGPRn
is the highest numbered SGPR
allocated to the wavefront).
FLAT_SCRATCH_HI is
multiplied by 256 (as it is
in units of 256 bytes) and
added to
``SH_HIDDEN_PRIVATE_BASE_VIMID``
to calculate the per wavefront
FLAT SCRATCH BASE in flat
memory instructions that
access the scratch
aperture.

The second SGPR is 32-bit
byte size of a single
work-item's scratch memory
usage. CP obtains this from
the runtime, and it is
always a multiple of DWORD.
CP checks that the value in
the kernel dispatch packet
Private Segment Byte Size is
not larger and requests the
runtime to increase the
queue's scratch size if
necessary. The kernel code
must move it to
FLAT_SCRATCH_LO which is
SGPRn-3 on GFX7 and SGPRn-5
on GFX8. FLAT_SCRATCH_LO is
used as the FLAT SCRATCH
SIZE in flat memory
instructions. Having CP load
it once avoids loading it at
the beginning of every
wavefront.
GFX9-GFX10
This is the
64-bit base address of the
per SPI scratch backing
memory managed by SPI for
the queue executing the
kernel dispatch. CP obtains
this from the runtime (and
divides it if there are
multiple Shader Arrays each
with its own SPI). The value
of Scratch Wavefront Offset must
be added by the kernel
machine code and the result
moved to the FLAT_SCRATCH
SGPR which is SGPRn-6 and
SGPRn-5. It is used as the
FLAT SCRATCH BASE in flat
memory instructions.
then Private Segment Size 1 The 32-bit byte size of a
(enable_sgpr_private single
work-item's
scratch_segment_size) memory
allocation. This is the
value from the kernel
dispatch packet Private
Segment Byte Size rounded up
by CP to a multiple of
DWORD.

Having CP load it once avoids
loading it at the beginning of
every wavefront.

This is not used for
GFX7-GFX8 since it is the same
value as the second SGPR of
Flat Scratch Init. However, it
may be needed for GFX9-GFX10 which
changes the meaning of the
Flat Scratch Init value.
then Grid Work-Group Count X 1 32-bit count of the number of
(enable_sgpr_grid work-groups in the X dimension
_workgroup_count_X) for the grid being
executed. Computed from the
fields in the kernel dispatch
packet as ((grid_size.x +
workgroup_size.x - 1) /
workgroup_size.x).
then Grid Work-Group Count Y 1 32-bit count of the number of
(enable_sgpr_grid work-groups in the Y dimension
_workgroup_count_Y && for the grid being
less than 16 previous executed. Computed from the
SGPRs) fields in the kernel dispatch
packet as ((grid_size.y +
workgroup_size.y - 1) /
workgroupSize.y).

Only initialized if `__