libc/src/unistd/linux/fork.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-exception
   6 //
   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/threads/fork_callbacks.h"
  14 #include "src/__support/threads/thread.h" // For thread self object
  15
  16 #include "src/errno/libc_errno.h"
  17 #include <signal.h>      // For SIGCHLD
  18 #include <sys/syscall.h> // For syscall numbers.
  19
  20 namespace LIBC_NAMESPACE {
  21
  22 // The implementation of fork here is very minimal. We will add more
  23 // functionality and standard compliance in future.
  24
  25 LLVM_LIBC_FUNCTION(pid_t, fork, (void)) {
  26   invoke_prepare_callbacks();
  27 #ifdef SYS_fork
  28   pid_t ret = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_fork);
  29 #elif defined(SYS_clone)
  30   pid_t ret = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_clone, SIGCHLD, 0);
  31 #else
  32 #error "fork and clone syscalls not available."
  33 #endif
  34   if (ret == 0) {
  35     // Return value is 0 in the child process.
  36     // The child is created with a single thread whose self object will be a
  37     // copy of parent process' thread which called fork. So, we have to fix up
  38     // the child process' self object with the new process' tid.
  39     self.attrib->tid = LIBC_NAMESPACE::syscall_impl<pid_t>(SYS_gettid);
  40     invoke_child_callbacks();
  41     return 0;
  42   }
  43
  44   if (ret < 0) {
  45     // Error case, a child process was not created.
  46     libc_errno = static_cast<int>(-ret);
  47     return -1;
  48   }
  49
  50   invoke_parent_callbacks();
  51   return ret;
  52 }
  53
  54 } // namespace LIBC_NAMESPACE