/* Copyright (C) 1999-2022 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>
#define _ERRNO_H	1
#include <bits/errno.h>
#include <tcb-offsets.h>

/* Clone the calling process, but without copying the whole address space.
   The calling process is suspended until the new process exits or is
   replaced by a call to `execve'.  Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */

ENTRY (__vfork)

	/* Pop the return PC value into ECX.  */
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	cfi_register (%eip, %ecx)

	/* Stuff the syscall number in EAX and enter into the kernel.  */
	movl	$SYS_ify (vfork), %eax
	int	$0x80

	/* Jump to the return PC.  Don't jump directly since this
	   disturbs the branch target cache.  Instead push the return
	   address back on the stack.  */
	pushl	%ecx
	cfi_adjust_cfa_offset (4)

	cmpl	$-4095, %eax
	/* Branch forward if it failed.  */
	jae	SYSCALL_ERROR_LABEL

#if SHSTK_ENABLED
	/* Check if shadow stack is in use.  */
	xorl	%edx, %edx
	rdsspd	%edx
	testl	%edx, %edx
	/* Normal return if shadow stack isn't in use.  */
	je	L(no_shstk)

	testl	%eax, %eax
	/* In parent, normal return.  */
	jnz	L(no_shstk)

	/* NB: In child, jump back to caller via indirect branch without
	   popping shadow stack which is shared with parent.  Keep shadow
	   stack mismatched so that child returns in the vfork-calling
	   function will trigger SIGSEGV.  */
	popl	%ecx
	cfi_adjust_cfa_offset (-4)
	jmp	*%ecx

L(no_shstk):
#endif

	ret

PSEUDO_END (__vfork)
libc_hidden_def (__vfork)

weak_alias (__vfork, vfork)
strong_alias (__vfork, __libc_vfork)
