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/* Copyright (C) 2001-2025 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
<https://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, pid_t *parent_tid, void *tls, pid_t *child_tid);
the kernel entry is:
int clone (long flags, void *child_stack, pid_t *parent_tid,
pid_t *child_tid, void *tls);
The parameters are passed in register and on the stack from userland:
rdi: fn
rsi: child_stack
rdx: flags
rcx: arg
r8: TID field in parent
r9: thread pointer
%rsp+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
/* Align stack to 16 bytes per the x86-64 psABI. */
andq $-16, %rsi
jz SYSCALL_ERROR_LABEL /* no NULL stack pointers */
/* Insert the argument onto the new stack. */
movq %rcx,-8(%rsi)
subq $16,%rsi
/* Save the function pointer. It will be popped off in the
child. */
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)
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