1 /* SPDX-License-Identifier: LGPL-2.1-or-later */
2 #pragma once
3
4 /***
5 Copyright © 2016 Michael Karcher
6 ***/
7
8 #include <errno.h>
9 #include <sched.h>
10 #include <sys/syscall.h>
11
12 #include "log.h"
13 #include "macro.h"
14
15 /**
16 * raw_clone() - uses clone to create a new process with clone flags
17 * @flags: Flags to pass to the clone system call
18 *
19 * Uses the clone system call to create a new process with the cloning flags and termination signal passed in the flags
20 * parameter. Opposed to glibc's clone function, using this function does not set up a separate stack for the child, but
21 * relies on copy-on-write semantics on the one stack at a common virtual address, just as fork does.
22 *
23 * To obtain copy-on-write semantics, flags must not contain CLONE_VM, and thus CLONE_THREAD and CLONE_SIGHAND (which
24 * require CLONE_VM) are not usable.
25 *
26 * Additionally, as this function does not pass the ptid, newtls and ctid parameters to the kernel, flags must not
27 * contain CLONE_PARENT_SETTID, CLONE_CHILD_SETTID, CLONE_CHILD_CLEARTID or CLONE_SETTLS.
28 *
29 * Returns: 0 in the child process and the child process id in the parent.
30 */
raw_clone(unsigned long flags)31 static inline pid_t raw_clone(unsigned long flags) {
32 pid_t ret;
33
34 assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
35 CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0);
36 #if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
37 /* On s390/s390x and cris the order of the first and second arguments
38 * of the raw clone() system call is reversed. */
39 ret = (pid_t) syscall(__NR_clone, NULL, flags);
40 #elif defined(__sparc__)
41 {
42 /**
43 * sparc always returns the other process id in %o0, and
44 * a boolean flag whether this is the child or the parent in
45 * %o1. Inline assembly is needed to get the flag returned
46 * in %o1.
47 */
48 int in_child, child_pid, error;
49
50 asm volatile("mov %3, %%g1\n\t"
51 "mov %4, %%o0\n\t"
52 "mov 0 , %%o1\n\t"
53 #if defined(__arch64__)
54 "t 0x6d\n\t"
55 #else
56 "t 0x10\n\t"
57 #endif
58 "addx %%g0, 0, %2\n\t"
59 "mov %%o1, %0\n\t"
60 "mov %%o0, %1" :
61 "=r"(in_child), "=r"(child_pid), "=r"(error) :
62 "i"(__NR_clone), "r"(flags) :
63 "%o1", "%o0", "%g1", "cc" );
64
65 if (error) {
66 errno = child_pid;
67 ret = -1;
68 } else
69 ret = in_child ? 0 : child_pid;
70 }
71 #else
72 ret = (pid_t) syscall(__NR_clone, flags, NULL);
73 #endif
74
75 if (ret == 0)
76 reset_cached_pid();
77
78 return ret;
79 }
80