1/* The clone3 syscall wrapper. Linux/x86-64 version.
2 Copyright (C) 2021-2023 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 in registers from userland:
31 rdi: cl_args
32 rsi: size
33 rdx: func
34 rcx: arg
35
36 The kernel expects:
37 rax: system call number
38 rdi: cl_args
39 rsi: size */
40
41 .text
42ENTRY (__clone3)
43 /* Sanity check arguments. */
44 movl $-EINVAL, %eax
45 test %RDI_LP, %RDI_LP /* No NULL cl_args pointer. */
46 jz SYSCALL_ERROR_LABEL
47 test %RDX_LP, %RDX_LP /* No NULL function pointer. */
48 jz SYSCALL_ERROR_LABEL
49
50 /* Save the cl_args pointer in R8 which is preserved by the
51 syscall. */
52 mov %RCX_LP, %R8_LP
53
54 /* Do the system call. */
55 movl $SYS_ify(clone3), %eax
56
57 /* End FDE now, because in the child the unwind info will be
58 wrong. */
59 cfi_endproc
60 syscall
61
62 test %RAX_LP, %RAX_LP
63 jl SYSCALL_ERROR_LABEL
64 jz L(thread_start)
65
66 ret
67
68L(thread_start):
69 cfi_startproc
70 /* Clearing frame pointer is insufficient, use CFI. */
71 cfi_undefined (rip)
72 /* Clear the frame pointer. The ABI suggests this be done, to mark
73 the outermost frame obviously. */
74 xorl %ebp, %ebp
75
76 /* Align stack to 16 bytes per the x86-64 psABI. */
77 and $-16, %RSP_LP
78
79 /* Set up arguments for the function call. */
80 mov %R8_LP, %RDI_LP /* Argument. */
81 call *%rdx /* Call function. */
82 /* Call exit with return value from function call. */
83 movq %rax, %rdi
84 movl $SYS_ify(exit), %eax
85 syscall
86 cfi_endproc
87
88 cfi_startproc
89PSEUDO_END (__clone3)
90
91libc_hidden_def (__clone3)
92weak_alias (__clone3, clone3)
93