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