/* Copyright (C) 2001-2018 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

   <http://www.gnu.org/licenses/>.  */

/* clone() is even more special than fork() as it mucks with stacks

   and invokes a function in the right context after its all over.  */

#include <sysdep.h>

#define _ERRNO_H	1

#include <bits/errno.h>

#include <asm-syntax.h>

/* The userland implementation is:

   int clone (int (*fn)(void *arg), void *child_stack, int flags, void *arg),

   the kernel entry is:

   int clone (long flags, void *child_stack).

   The parameters are passed in register and on the stack from userland:

   rdi: fn

   rsi: child_stack

   rdx:	flags

   rcx: arg

   r8d:	TID field in parent

   r9d: thread pointer

%esp+8:	TID field in child

   The kernel expects:

   rax: system call number

   rdi: flags

   rsi: child_stack

   rdx: TID field in parent

   r10: TID field in child

   r8:	thread pointer  */

        .text

ENTRY (__clone)

	/* Sanity check arguments.  */

	movq	$-EINVAL,%rax

	testq	%rdi,%rdi		/* no NULL function pointers */

	jz	SYSCALL_ERROR_LABEL

	testq	%rsi,%rsi		/* no NULL stack pointers */

	jz	SYSCALL_ERROR_LABEL

	/* Insert the argument onto the new stack.  */

	subq	$16,%rsi

	movq	%rcx,8(%rsi)

	/* Save the function pointer.  It will be popped off in the

	   child in the ebx frobbing below.  */

	movq	%rdi,0(%rsi)

	/* Do the system call.  */

	movq	%rdx, %rdi

	movq	%r8, %rdx

	movq	%r9, %r8

	mov	8(%rsp), %R10_LP

	movl	$SYS_ify(clone),%eax

	/* End FDE now, because in the child the unwind info will be

	   wrong.  */

	cfi_endproc;

	syscall

	testq	%rax,%rax

	jl	SYSCALL_ERROR_LABEL

	jz	L(thread_start)

	ret

L(thread_start):

	cfi_startproc;

	/* Clearing frame pointer is insufficient, use CFI.  */

	cfi_undefined (rip);

	/* Clear the frame pointer.  The ABI suggests this be done, to mark

	   the outermost frame obviously.  */

	xorl	%ebp, %ebp

	/* Set up arguments for the function call.  */

	popq	%rax		/* Function to call.  */

	popq	%rdi		/* Argument.  */

	call	*%rax

	/* Call exit with return value from function call. */

	movq	%rax, %rdi

	movl	$SYS_ify(exit), %eax

	syscall

	cfi_endproc;

	cfi_startproc;

PSEUDO_END (__clone)

libc_hidden_def (__clone)

weak_alias (__clone, clone)