1/* Copyright (C) 1999-2022 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 <https://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/* Clone the calling process, but without copying the whole address space.
24 The calling process is suspended until the new process exits or is
25 replaced by a call to `execve'. Return -1 for errors, 0 to the new process,
26 and the process ID of the new process to the old process. */
27
28ENTRY (__vfork)
29
30 /* Pop the return PC value into ECX. */
31 popl %ecx
32 cfi_adjust_cfa_offset (-4)
33 cfi_register (%eip, %ecx)
34
35 /* Stuff the syscall number in EAX and enter into the kernel. */
36 movl $SYS_ify (vfork), %eax
37 int $0x80
38
39 /* Jump to the return PC. Don't jump directly since this
40 disturbs the branch target cache. Instead push the return
41 address back on the stack. */
42 pushl %ecx
43 cfi_adjust_cfa_offset (4)
44
45 cmpl $-4095, %eax
46 /* Branch forward if it failed. */
47 jae SYSCALL_ERROR_LABEL
48
49#if SHSTK_ENABLED
50 /* Check if shadow stack is in use. */
51 xorl %edx, %edx
52 rdsspd %edx
53 testl %edx, %edx
54 /* Normal return if shadow stack isn't in use. */
55 je L(no_shstk)
56
57 testl %eax, %eax
58 /* In parent, normal return. */
59 jnz L(no_shstk)
60
61 /* NB: In child, jump back to caller via indirect branch without
62 popping shadow stack which is shared with parent. Keep shadow
63 stack mismatched so that child returns in the vfork-calling
64 function will trigger SIGSEGV. */
65 popl %ecx
66 cfi_adjust_cfa_offset (-4)
67 jmp *%ecx
68
69L(no_shstk):
70#endif
71
72 ret
73
74PSEUDO_END (__vfork)
75libc_hidden_def (__vfork)
76
77weak_alias (__vfork, vfork)
78strong_alias (__vfork, __libc_vfork)
79

source code of glibc/sysdeps/unix/sysv/linux/i386/vfork.S