1/* Copyright (C) 2001-2022 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/* clone() is even more special than fork() as it mucks with stacks
19   and invokes a function in the right context after its all over.  */
20
21#include <sysdep.h>
22#define _ERRNO_H	1
23#include <bits/errno.h>
24#include <asm-syntax.h>
25
26/* The userland implementation is:
27   int clone (int (*fn)(void *arg), void *child_stack, int flags,
28	      void *arg, pid_t *parent_tid, void *tls, pid_t *child_tid);
29   the kernel entry is:
30   int clone (long flags, void *child_stack, pid_t *parent_tid,
31	      pid_t *child_tid, void *tls);
32
33   The parameters are passed in register and on the stack from userland:
34   rdi: fn
35   rsi: child_stack
36   rdx:	flags
37   rcx: arg
38    r8:	TID field in parent
39    r9: thread pointer
40%rsp+8:	TID field in child
41
42   The kernel expects:
43   rax: system call number
44   rdi: flags
45   rsi: child_stack
46   rdx: TID field in parent
47   r10: TID field in child
48   r8:	thread pointer  */
49
50
51        .text
52ENTRY (__clone)
53	/* Sanity check arguments.  */
54	movq	$-EINVAL,%rax
55	testq	%rdi,%rdi		/* no NULL function pointers */
56	jz	SYSCALL_ERROR_LABEL
57
58	/* Align stack to 16 bytes per the x86-64 psABI.  */
59	andq	$-16, %rsi
60	jz	SYSCALL_ERROR_LABEL	/* no NULL stack pointers */
61
62	/* Insert the argument onto the new stack.  */
63	movq	%rcx,-8(%rsi)
64
65	subq	$16,%rsi
66
67	/* Save the function pointer.  It will be popped off in the
68	   child.  */
69	movq	%rdi,0(%rsi)
70
71	/* Do the system call.  */
72	movq	%rdx, %rdi
73	movq	%r8, %rdx
74	movq	%r9, %r8
75	mov	8(%rsp), %R10_LP
76	movl	$SYS_ify(clone),%eax
77
78	/* End FDE now, because in the child the unwind info will be
79	   wrong.  */
80	cfi_endproc;
81	syscall
82
83	testq	%rax,%rax
84	jl	SYSCALL_ERROR_LABEL
85	jz	L(thread_start)
86
87	ret
88
89L(thread_start):
90	cfi_startproc;
91	/* Clearing frame pointer is insufficient, use CFI.  */
92	cfi_undefined (rip);
93	/* Clear the frame pointer.  The ABI suggests this be done, to mark
94	   the outermost frame obviously.  */
95	xorl	%ebp, %ebp
96
97	/* Set up arguments for the function call.  */
98	popq	%rax		/* Function to call.  */
99	popq	%rdi		/* Argument.  */
100	call	*%rax
101	/* Call exit with return value from function call. */
102	movq	%rax, %rdi
103	movl	$SYS_ify(exit), %eax
104	syscall
105	cfi_endproc;
106
107	cfi_startproc;
108PSEUDO_END (__clone)
109
110libc_hidden_def (__clone)
111weak_alias (__clone, clone)
112