1/* Copyright (C) 2001-2021 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 RDI. We need a register that
31 is preserved by the syscall and that we're allowed to destroy. */
32 popq %rdi
33 cfi_adjust_cfa_offset(-8)
34 cfi_register(%rip, %rdi)
35
36 /* Stuff the syscall number in RAX and enter into the kernel. */
37 movl $SYS_ify (vfork), %eax
38 syscall
39
40 /* Push back the return PC. */
41 pushq %rdi
42 cfi_adjust_cfa_offset(8)
43
44 cmpl $-4095, %eax
45 jae SYSCALL_ERROR_LABEL /* Branch forward if it failed. */
46
47#if SHSTK_ENABLED
48 /* Check if shadow stack is in use. */
49 xorl %esi, %esi
50 rdsspq %rsi
51 testq %rsi, %rsi
52 /* Normal return if shadow stack isn't in use. */
53 je L(no_shstk)
54
55 testl %eax, %eax
56 /* In parent, normal return. */
57 jnz L(no_shstk)
58
59 /* NB: In child, jump back to caller via indirect branch without
60 popping shadow stack which is shared with parent. Keep shadow
61 stack mismatched so that child returns in the vfork-calling
62 function will trigger SIGSEGV. */
63 popq %rdi
64 cfi_adjust_cfa_offset(-8)
65 jmp *%rdi
66
67L(no_shstk):
68#endif
69
70 /* Normal return. */
71 ret
72
73PSEUDO_END (__vfork)
74libc_hidden_def (__vfork)
75
76weak_alias (__vfork, vfork)
77strong_alias (__vfork, __libc_vfork)
78