1/* Copyright (C) 2001-2021 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