thrd_create.cpp
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//===-- Linux implementation of the thrd_create function ------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#include "config/linux/syscall.h" // For syscall function.
#include "include/errno.h" // For E* error values.
#include "include/sys/mman.h" // For PROT_* and MAP_* definitions.
#include "include/sys/syscall.h" // For syscall numbers.
#include "include/threads.h" // For thrd_* type definitions.
#include "src/__support/common.h"
#include "src/errno/llvmlibc_errno.h"
#include "src/sys/mman/mmap.h"
#include "src/sys/mman/munmap.h"
#include "src/threads/linux/thread_utils.h"
#include <linux/futex.h> // For futex operations.
#include <linux/sched.h> // For CLONE_* flags.
#include <stdint.h>
namespace __llvm_libc {
struct StartArgs {
thrd_t *thread;
thrd_start_t func;
void *arg;
};
static __attribute__((noinline)) void start_thread() {
StartArgs *start_args = reinterpret_cast<StartArgs *>(get_start_args_addr());
__llvm_libc::syscall(SYS_exit, start_args->thread->__retval =
start_args->func(start_args->arg));
}
int LLVM_LIBC_ENTRYPOINT(thrd_create)(thrd_t *thread, thrd_start_t func,
void *arg) {
unsigned clone_flags =
CLONE_VM // Share the memory space with the parent.
| CLONE_FS // Share the file system with the parent.
| CLONE_FILES // Share the files with the parent.
| CLONE_SIGHAND // Share the signal handlers with the parent.
| CLONE_THREAD // Same thread group as the parent.
| CLONE_SYSVSEM // Share a single list of System V semaphore adjustment
// values
| CLONE_PARENT_SETTID // Set child thread ID in |ptid| of the parent.
| CLONE_CHILD_CLEARTID; // Let the kernel clear the tid address and futex
// wake the joining thread.
// TODO: Add the CLONE_SETTLS flag and setup the TLS area correctly when
// making the clone syscall.
void *stack = __llvm_libc::mmap(nullptr, ThreadParams::DefaultStackSize,
PROT_READ | PROT_WRITE,
MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (stack == MAP_FAILED)
return llvmlibc_errno == ENOMEM ? thrd_nomem : thrd_error;
thread->__stack = stack;
thread->__stack_size = ThreadParams::DefaultStackSize;
thread->__retval = -1;
FutexData *clear_tid_address =
reinterpret_cast<FutexData *>(thread->__clear_tid);
*clear_tid_address = ThreadParams::ClearTIDValue;
// When the new thread is spawned by the kernel, the new thread gets the
// stack we pass to the clone syscall. However, this stack is empty and does
// not have any local vars present in this function. Hence, one cannot
// pass arguments to the thread start function, or use any local vars from
// here. So, we pack them into the new stack from where the thread can sniff
// them out.
uintptr_t adjusted_stack = reinterpret_cast<uintptr_t>(stack) +
ThreadParams::DefaultStackSize - sizeof(StartArgs);
StartArgs *start_args = reinterpret_cast<StartArgs *>(adjusted_stack);
start_args->thread = thread;
start_args->func = func;
start_args->arg = arg;
// TODO: The arguments to the clone syscall below is correct for x86_64
// but it might differ for other architectures. So, make this call
// architecture independent. May be implement a glibc like wrapper for clone
// and use it here.
long clone_result =
__llvm_libc::syscall(SYS_clone, clone_flags, adjusted_stack,
&thread->__tid, clear_tid_address, 0);
if (clone_result == 0) {
start_thread();
} else if (clone_result < 0) {
int error_val = -clone_result;
return error_val == ENOMEM ? thrd_nomem : thrd_error;
}
return thrd_success;
}
} // namespace __llvm_libc