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/* SPDX-License-Identifier: LGPL-2.1-or-later */
#pragma once
/***
Copyright © 2016 Michael Karcher
***/
#include <errno.h>
#include <sched.h>
#include <sys/syscall.h>
#include "log.h"
#include "macro.h"
#include "process-util.h"
/**
* raw_clone() - uses clone to create a new process with clone flags
* @flags: Flags to pass to the clone system call
*
* Uses the clone system call to create a new process with the cloning flags and termination signal passed in the flags
* parameter. Opposed to glibc's clone function, using this function does not set up a separate stack for the child, but
* relies on copy-on-write semantics on the one stack at a common virtual address, just as fork does.
*
* To obtain copy-on-write semantics, flags must not contain CLONE_VM, and thus CLONE_THREAD and CLONE_SIGHAND
* (which require CLONE_VM) are not usable.
*
* Additionally, as this function does not pass the ptid (pidfd in the case of CLONE_PIDFD), newtls and ctid
* parameters to the kernel, flags must not contain CLONE_PARENT_SETTID, CLONE_CHILD_SETTID, CLONE_CHILD_CLEARTID,
* CLONE_SETTLS, or CLONE_PIDFD.
*
* WARNING: 💣 this call (just like glibc's own clone() wrapper) will not synchronize on glibc's malloc
* locks, which means they will be in an undefined state in the child if the parent is
* threaded. This means: the parent must either never use threads, or the child cannot use memory
* allocation itself. This is a major pitfall, hence be careful! 💣
*
* Returns: 0 in the child process and the child process id in the parent.
*/
static inline pid_t raw_clone(unsigned long flags) {
pid_t ret;
assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|CLONE_CHILD_CLEARTID|CLONE_SETTLS|CLONE_PIDFD)) == 0);
#if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
/* On s390/s390x and cris the order of the first and second arguments
* of the raw clone() system call is reversed. */
ret = (pid_t) syscall(__NR_clone, NULL, flags);
#elif defined(__sparc__)
{
/**
* sparc always returns the other process id in %o0, and
* a boolean flag whether this is the child or the parent in
* %o1. Inline assembly is needed to get the flag returned
* in %o1.
*/
int in_child, child_pid, error;
asm volatile("mov %3, %%g1\n\t"
"mov %4, %%o0\n\t"
"mov 0 , %%o1\n\t"
#if defined(__arch64__)
"t 0x6d\n\t"
#else
"t 0x10\n\t"
#endif
"addx %%g0, 0, %2\n\t"
"mov %%o1, %0\n\t"
"mov %%o0, %1" :
"=r"(in_child), "=r"(child_pid), "=r"(error) :
"i"(__NR_clone), "r"(flags) :
"%o1", "%o0", "%g1", "cc" );
if (error) {
errno = child_pid;
ret = -1;
} else
ret = in_child ? 0 : child_pid;
}
#else
ret = (pid_t) syscall(__NR_clone, flags, NULL);
#endif
if (ret == 0)
reset_cached_pid();
return ret;
}
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