1/* The clone3 syscall wrapper.  Linux/i386 version.
2   Copyright (C) 2021 Free Software Foundation, Inc.
3   This file is part of the GNU C Library.
4
5   The GNU C Library is free software; you can redistribute it and/or
6   modify it under the terms of the GNU Lesser General Public
7   License as published by the Free Software Foundation; either
8   version 2.1 of the License, or (at your option) any later version.
9
10   The GNU C Library is distributed in the hope that it will be useful,
11   but WITHOUT ANY WARRANTY; without even the implied warranty of
12   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13   Lesser General Public License for more details.
14
15   You should have received a copy of the GNU Lesser General Public
16   License along with the GNU C Library; if not, see
17   <https://www.gnu.org/licenses/>.  */
18
19/* clone3() is even more special than fork() as it mucks with stacks
20   and invokes a function in the right context after its all over.  */
21
22#include <sysdep.h>
23
24/* The userland implementation is:
25   int clone3 (struct clone_args *cl_args, size_t size,
26	       int (*func)(void *arg), void *arg);
27   the kernel entry is:
28   int clone3 (struct clone_args *cl_args, size_t size);
29
30   The parameters are passed on stack from userland:
31   16(%esp)	arg
32   12(%esp)	func
33    8(%esp)	size
34    4(%esp)	cl_args
35     (%esp)	Return address
36
37   The kernel expects:
38   eax:		system call number
39   ebx:		cl_args
40   ecx:		size
41 */
42
43#define CL_ARGS	4
44#define SIZE	8
45#define FUNC	12
46#define ARG	16
47
48        .text
49ENTRY (__clone3)
50	/* Sanity check arguments.  */
51	movl	$-EINVAL, %eax
52	movl	CL_ARGS(%esp), %ecx	/* No NULL cl_args pointer.  */
53	testl	%ecx, %ecx
54	jz	SYSCALL_ERROR_LABEL
55	/* Save the function pointer in EDX which is preserved by the
56	   system call.  */
57	movl	FUNC(%esp), %edx	/* No NULL function pointer.  */
58	testl	%edx, %edx
59	jz	SYSCALL_ERROR_LABEL
60
61	/* Save EBX and ESI.  */
62	pushl	%ebx
63	cfi_adjust_cfa_offset (4)
64	pushl	%esi
65	cfi_adjust_cfa_offset (4)
66
67	/* Save the function argument in ESI which is preserved by the
68	   system call.  */
69	movl	(ARG + 8)(%esp), %esi
70
71	/* Put cl_args in EBX.  */
72	movl	%ecx, %ebx
73
74	/* Put size in ECX.  */
75	movl	(SIZE + 8)(%esp), %ecx
76
77	/* Do the system call.  */
78	movl	$SYS_ify(clone3), %eax
79
80	/* End FDE now, because in the child the unwind info will be
81	   wrong.  */
82	cfi_endproc
83
84	int	$0x80
85	test	%eax, %eax
86	/* No need to restore EBX and ESI in child.  */
87	jz	L(thread_start)
88
89	/* Restore EBX and ESI in parent.  */
90	pop	%esi
91	pop	%ebx
92	jl	SYSCALL_ERROR_LABEL
93
94	ret
95
96L(thread_start):
97	cfi_startproc
98	/* Clearing frame pointer is insufficient, use CFI.  */
99	cfi_undefined (eip)
100	xorl	%ebp, %ebp	/* Terminate the stack frame.  */
101
102	/* Align stack to 16 bytes per the i386 psABI.  */
103	andl	$-16, %esp
104
105	/* The PUSH below will decrement stack pointer by 4 bytes.  */
106	subl	$12, %esp
107
108	/* Set up the argument for the function call.  */
109	pushl	%esi		/* Argument.  */
110	cfi_adjust_cfa_offset (4)
111	call	*%edx		/* Call function.  */
112
113	/* Call exit with return value from function call. */
114	movl	%eax, %ebx
115	movl	$SYS_ify(exit), %eax
116	ENTER_KERNEL
117	cfi_endproc
118
119	cfi_startproc
120PSEUDO_END (__clone3)
121
122libc_hidden_def (__clone3)
123weak_alias (__clone3, clone3)
124