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