1/* Copyright (C) 2001-2016 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <http://www.gnu.org/licenses/>. */
17
18#include <sysdep.h>
19#define _ERRNO_H 1
20#include <bits/errno.h>
21#include <tcb-offsets.h>
22
23
24/* Clone the calling process, but without copying the whole address space.
25 The calling process is suspended until the new process exits or is
26 replaced by a call to `execve'. Return -1 for errors, 0 to the new process,
27 and the process ID of the new process to the old process. */
28
29ENTRY (__vfork)
30
31 /* Pop the return PC value into RDI. We need a register that
32 is preserved by the syscall and that we're allowed to destroy. */
33 popq %rdi
34 cfi_adjust_cfa_offset(-8)
35 cfi_register(%rip, %rdi)
36
37 /* Save the TCB-cached PID away in %esi, and then negate the TCB
38 field. But if it's zero, set it to 0x80000000 instead. See
39 raise.c for the logic that relies on this value. */
40 movl %fs:PID, %esi
41 movl $0x80000000, %ecx
42 movl %esi, %edx
43 negl %edx
44 cmove %ecx, %edx
45 movl %edx, %fs:PID
46
47 /* Stuff the syscall number in RAX and enter into the kernel. */
48 movl $SYS_ify (vfork), %eax
49 syscall
50
51 /* Push back the return PC. */
52 pushq %rdi
53 cfi_adjust_cfa_offset(8)
54
55 /* Restore the original value of the TCB cache of the PID, if we're
56 the parent. But in the child (syscall return value equals zero),
57 leave things as they are. */
58 testq %rax, %rax
59 je 1f
60 movl %esi, %fs:PID
611:
62
63 cmpl $-4095, %eax
64 jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */
65
66 /* Normal return. */
67 ret
68
69PSEUDO_END (__vfork)
70libc_hidden_def (__vfork)
71
72weak_alias (__vfork, vfork)
73strong_alias (__vfork, __libc_vfork)
74