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/* The clone3 syscall wrapper. Linux/x86-64 version.
Copyright (C) 2021-2022 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/>. */
/* clone3() 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>
/* The userland implementation is:
int clone3 (struct clone_args *cl_args, size_t size,
int (*func)(void *arg), void *arg);
the kernel entry is:
int clone3 (struct clone_args *cl_args, size_t size);
The parameters are passed in registers from userland:
rdi: cl_args
rsi: size
rdx: func
rcx: arg
The kernel expects:
rax: system call number
rdi: cl_args
rsi: size */
.text
ENTRY (__clone3)
/* Sanity check arguments. */
movl $-EINVAL, %eax
test %RDI_LP, %RDI_LP /* No NULL cl_args pointer. */
jz SYSCALL_ERROR_LABEL
test %RDX_LP, %RDX_LP /* No NULL function pointer. */
jz SYSCALL_ERROR_LABEL
/* Save the cl_args pointer in R8 which is preserved by the
syscall. */
mov %RCX_LP, %R8_LP
/* Do the system call. */
movl $SYS_ify(clone3), %eax
/* End FDE now, because in the child the unwind info will be
wrong. */
cfi_endproc
syscall
test %RAX_LP, %RAX_LP
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
/* Align stack to 16 bytes per the x86-64 psABI. */
and $-16, %RSP_LP
/* Set up arguments for the function call. */
mov %R8_LP, %RDI_LP /* Argument. */
call *%rdx /* Call function. */
/* Call exit with return value from function call. */
movq %rax, %rdi
movl $SYS_ify(exit), %eax
syscall
cfi_endproc
cfi_startproc
PSEUDO_END (__clone3)
libc_hidden_def (__clone3)
weak_alias (__clone3, clone3)
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