src/basic/raw-clone.h

   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  */
  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 }