lld 11.0.0 Release Notes

Introduction

This document contains the release notes for the lld linker, release 11.0.0. Here we describe the status of lld, including major improvements from the previous release. All lld releases may be downloaded from the LLVM releases web site.

Non-comprehensive list of changes in this release

ELF Improvements

• --lto-emit-asm is added to emit assembly output for debugging purposes. (D77231)
• --lto-whole-program-visibility is added to specify that classes have hidden LTO visibility in LTO and ThinLTO links of source files compiled with -fwhole-program-vtables. See LTOVisibility for details. (D71913)
• --print-archive-stats= is added to print the number of members and the number of fetched members for each archive. The feature is similar to GNU gold's --print-symbol-counts=. (D78983)
• --shuffle-sections= is added to introduce randomization in the output to help reduce measurement bias and detect static initialization order fiasco. (D74791) (D74887)
• --time-trace is added. It records a time trace file that can be viewed in chrome://tracing. The file can be specified with --time-trace-file. Trace granularity can be specified with --time-trace-granularity. (D71060)
• --thinlto-single-module is added to compile a subset of modules in ThinLTO for debugging purposes. (D80406)
• --unique is added to create separate output sections for orphan sections. (D75536)
• --warn-backrefs has been improved to emulate GNU ld's archive semantics. If a link passes with warnings from --warn-backrefs, it almost assuredly means that the link will fail with GNU ld, or the symbol will get different resolutions in GNU ld and LLD. --warn-backrefs-exclude= is added to exclude known issues. (D77522) (D77630) (D77512)
• --no-relax is accepted but ignored. The Linux kernel's RISC-V port uses this option. (D81359)
• --rosegment (default) is added to complement --no-rosegment. GNU gold from 2.35 onwards support both options.
• --threads=N is added. The default uses all threads. (D76885)
• --wrap has better compatibility with GNU ld.
• -z dead-reloc-in-nonalloc=<section_glob>=<value> is added to resolve an absolute relocation referencing a discarded symbol. (D83264)
• Changed tombstone values to (.debug_ranges/.debug_loc) 1 and (other .debug_*) 0. A tombstone value is the computed value of a relocation referencing a discarded symbol (--gc-sections, ICF or /DISCARD/). (D84825) In the future many .debug_* may switch to 0xffffffff/0xffffffffffffffff as the tombstone value.
• -z keep-text-section-prefix moves .text.unknown.* input sections to .text.unknown.
• -z rel and -z rela are added to select the REL/RELA format for dynamic relocations. The default is target specific and typically matches the form used in relocatable objects.
• -z start-stop-visibility={default,protected,internal,hidden} is added. GNU ld/gold from 2.35 onwards support this option. (D55682)
• When -r or --emit-relocs is specified, the GNU ld compatible --discard-all and --discard-locals semantics are implemented. (D77807)
• --emit-relocs --strip-debug can now be used together. (D74375)
• --gdb-index supports DWARF v5. (D79061) (D85579)
• -r allows SHT_X86_64_UNWIND to be merged into SHT_PROGBITS. This allows clang/GCC produced object files to be mixed together. (D85785)
• Better linker script support related to output section alignments and LMA regions. (D74286) (D74297) (D75724) (D81986)
• In a input section description, the filename can be specified in double quotes. archive:file syntax is added. (D72517) (D75100)
• Linker script specified empty (.init|.preinit|.fini)_array are allowed with RELRO. (D76915)
• INSERT AFTER and INSERT BEFORE work for orphan sections now. (D74375)
• INPUT_SECTION_FLAGS is supported in linker scripts. (D72745)
• DF_1_PIE is set for position-independent executables. (D80872)
• For a symbol assignment alias = aliasee;, alias inherits the aliasee's symbol type. (D86263)
• SHT_GNU_verneed in shared objects are parsed, and versioned undefined symbols in shared objects are respected. (D80059)
• SHF_LINK_ORDER and non-SHF_LINK_ORDER sections can be mixed along as the SHF_LINK_ORDER components are contiguous. (D77007)
• An out-of-range relocation diagnostic mentions the referenced symbol now. (D73518)
• AArch64: R_AARCH64_PLT32 is supported. (D81184)
• ARM: SBREL type relocations are supported. (D74375)
• ARM: R_ARM_ALU_PC_G0, R_ARM_LDR_PC_G0, R_ARM_THUMB_PC8 and R_ARM_THUMB__PC12 are supported. (D75349) (D77200)
• ARM: various improvements to .ARM.exidx: /DISCARD/ support for a subset, out-of-range handling, support for non monotonic section order. (PR44824)
• AVR: many relocation types are supported. (D78741)
• Hexagon: General Dynamic and some other relocation types are supported.
• PPC: Canonical PLT and range extension thunks with addends are supported. (D73399) (D73424) (D75394)
• PPC and PPC64: copy relocations. (D73255)
• PPC64: _savegpr[01]_{14..31} and _restgpr[01]_{14..31} can be synthesized. (D79977)
• PPC64: R_PPC64_GOT_PCREL34 and R_PPC64_REL24_NOTOC are supported. r2 save stub is supported. (D81948) (D82950) (D82816)
• RISC-V: R_RISCV_IRELATIVE is supported. (D74022)
• RISC-V: R_RISCV_ALIGN is errored because GNU ld style linker relaxation is not supported. (D71820)
• SPARCv9: more relocation types are supported. (D77672)

Breaking changes

• One-dash form of some long option (--thinlto-*, --lto-*, --shuffle-sections=) are no longer supported. (D79371)
• --export-dynamic-symbol no longer implies -u. The new behavior matches GNU ld from binutils 2.35 onwards. (D80487)
• ARM: the default max page size was increased from 4096 to 65536. This increases compatibility with systems where a non standard page size was configured. This also is inline with GNU ld defaults. (D77330)
• ARM: for non-STT_FUNC symbols, Thumb interworking thunks are not added and BL/BLX are not substituted. (D73474) (D73542)
• AArch64: --force-bti is renamed to -z force-bti`. ``--pac-plt is renamed to -z pac-plt. This change is compatibile with GNU ld.
• A readonly PT_LOAD is created in the presence of a SECTIONS command. The new behavior is consistent with the longstanding behavior in the absence of a SECTIONS command.
• Orphan section names like .rodata.foo and .text.foo are not grouped into .rodata and .text in the presence of a SECTIONS command. The new behavior matches GNU ld. (D75225)
• --no-threads is removed. Use --threads=1 instead. --threads (no-op) is removed.

COFF Improvements

• Fixed exporting symbols whose names contain a period (.), which was a regression in lld 7.

MinGW Improvements

• Implemented new options for disabling auto import and runtime pseudo relocations (--disable-auto-import and --disable-runtime-pseudo-reloc), the --no-seh flag and options for selecting file and section alignment (--file-alignment and --section-alignment).