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/* Copyright (C) 1996-2025 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 <tcb-offsets.h>
/* Non-thread code calls __clone with the following parameters:
int clone(int (*fn)(void *arg),
void *child_stack,
int flags,
void *arg)
NPTL Code will call __clone with the following parameters:
int clone(int (*fn)(void *arg),
void *child_stack,
int flags,
void *arg,
int *parent_tidptr,
struct user_desc *newtls,
int *child_pidptr)
The code should not mangle the extra input registers.
Syscall expects: Input to __clone:
4(r25) - function pointer (r26, arg0)
0(r25) - argument (r23, arg3)
r26 - clone flags. (r24, arg2)
r25+64 - user stack pointer. (r25, arg1)
r24 - parent tid pointer. (stack - 52)
r23 - struct user_desc newtls pointer. (stack - 56)
r22 - child tid pointer. (stack - 60)
r20 - clone syscall number (constant)
Return:
On success the thread ID of the child process is returned in
the callers context.
On error return -1, and set errno to the value returned by
the syscall.
*/
.text
ENTRY(__clone)
/* Sanity check arguments. */
comib,=,n 0,%arg0,.LerrorSanity /* no NULL function pointers */
comib,=,n 0,%arg1,.LerrorSanity /* no NULL stack pointers */
/* Ensure stack argument is 8-byte aligned. */
ldo 7(%r25),%r25
depi 0,31,3,%r25
/* Save the function pointer, arg, and flags on the new stack. */
stwm %r26, 64(%r25)
stw %r23, -60(%r25)
stw %r24, -56(%r25)
/* Clone arguments are (int flags, void * child_stack) */
copy %r24, %r26 /* flags are first */
/* User stack pointer is in the correct register already */
/* Load args from stack... */
ldw -52(%sp), %r24 /* Load parent_tidptr */
ldw -56(%sp), %r23 /* Load newtls */
ldw -60(%sp), %r22 /* Load child_tidptr */
/* Do the system call */
ble 0x100(%sr2, %r0)
ldi __NR_clone, %r20
ldi -4096, %r1
comb,<<,n %r1, %ret0, .LerrorRest /* Note: unsigned compare. */
comib,=,n 0, %ret0, .LthreadStart
bv,n %r0(%rp)
.LerrorSanity:
/* Sanity checks failed, set errno to EINVAL. */
ldi -EINVAL, %ret0
.LerrorRest:
/* Something bad happened -- no child created -- need a frame */
ldo 64(%sp),%sp
.cfi_def_cfa_offset -64
bl __syscall_error, %rp
sub %r0, %ret0, %arg0
ldw -84(%sp), %rp
/* Return after setting errno, ret0 is set to -1 by __syscall_error. */
bv %r0(%rp)
ldo -64(%sp), %sp
.LthreadStart:
/* Load up the arguments. */
ldw -60(%sp), %arg0
ldw -64(%sp), %r22
/* $$dyncall fixes child's PIC register */
/* Call the user's function */
bl $$dyncall, %r31
copy %r31, %rp
copy %r28, %r26
ble 0x100(%sr2, %r0)
ldi __NR_exit, %r20
/* We should not return from exit.
We do not restore the stack state. */
iitlbp %r0, (%sr0, %r0)
PSEUDO_END(__clone)
libc_hidden_def (__clone)
weak_alias (__clone, clone)
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