64 lines · cpp
1//===-- Linux implementation of fork --------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#include "src/unistd/fork.h"10 11#include "src/__support/OSUtil/syscall.h" // For internal syscall function.12#include "src/__support/common.h"13#include "src/__support/macros/config.h"14#include "src/__support/threads/fork_callbacks.h"15#include "src/__support/threads/identifier.h"16#include "src/__support/threads/thread.h" // For thread self object17 18#include "src/__support/libc_errno.h"19#include <signal.h> // For SIGCHLD20#include <sys/syscall.h> // For syscall numbers.21 22namespace LIBC_NAMESPACE_DECL {23 24// The implementation of fork here is very minimal. We will add more25// functionality and standard compliance in future.26 27LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {28 invoke_prepare_callbacks();29 pid_t parent_tid = internal::gettid();30 // Invalidate parent's tid cache before forking. We cannot do this in child31 // process because in the post-fork instruction windows, there may be a signal32 // handler triggered which may get the wrong tid.33 internal::force_set_tid(0);34#ifdef SYS_fork35 pid_t ret = syscall_impl<pid_t>(SYS_fork);36#elif defined(SYS_clone)37 pid_t ret = syscall_impl<pid_t>(SYS_clone, SIGCHLD, 0);38#else39#error "fork and clone syscalls not available."40#endif41 42 if (ret == 0) {43 // Return value is 0 in the child process.44 // The child is created with a single thread whose self object will be a45 // copy of parent process' thread which called fork. So, we have to fix up46 // the child process' self object with the new process' tid.47 internal::force_set_tid(syscall_impl<pid_t>(SYS_gettid));48 invoke_child_callbacks();49 return 0;50 }51 52 if (ret < 0) {53 // Error case, a child process was not created.54 libc_errno = static_cast<int>(-ret);55 return -1;56 }57 // recover parent's tid.58 internal::force_set_tid(parent_tid);59 invoke_parent_callbacks();60 return ret;61}62 63} // namespace LIBC_NAMESPACE_DECL64