src/basic/raw-clone.h

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 #pragma once
   3
   4 /***
   5   This file is part of systemd.
   6
   7   Copyright 2010 Lennart Poettering
   8   Copyright 2016 Michael Karcher
   9 ***/
  10
  11 #include <sched.h>
  12 #include <sys/syscall.h>
  13
  14 #include "log.h"
  15 #include "macro.h"
  16
  17 /**
  18  * raw_clone() - uses clone to create a new process with clone flags
  19  * @flags: Flags to pass to the clone system call
  20  *
  21  * Uses the clone system call to create a new process with the cloning flags and termination signal passed in the flags
  22  * parameter. Opposed to glibc's clone funtion, using this function does not set up a separate stack for the child, but
  23  * relies on copy-on-write semantics on the one stack at a common virtual address, just as fork does.
  24  *
  25  * To obtain copy-on-write semantics, flags must not contain CLONE_VM, and thus CLONE_THREAD and CLONE_SIGHAND (which
  26  * require CLONE_VM) are not usable.
  27  *
  28  * Additionally, as this function does not pass the ptid, newtls and ctid parameters to the kernel, flags must not
  29  * contain CLONE_PARENT_SETTID, CLONE_CHILD_SETTID, CLONE_CHILD_CLEARTID or CLONE_SETTLS.
  30  *
  31  * Returns: 0 in the child process and the child process id in the parent.
  32  */
  33 static inline pid_t raw_clone(unsigned long flags) {
  34         pid_t ret;
  35
  36         assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
  37                          CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0);
  38 #if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
  39         /* On s390/s390x and cris the order of the first and second arguments
  40          * of the raw clone() system call is reversed. */
  41         ret = (pid_t) syscall(__NR_clone, NULL, flags);
  42 #elif defined(__sparc__) && defined(__arch64__)
  43         {
  44                 /**
  45                  * sparc64 always returns the other process id in %o0, and
  46                  * a boolean flag whether this is the child or the parent in
  47                  * %o1. Inline assembly is needed to get the flag returned
  48                  * in %o1.
  49                  */
  50                 int in_child, child_pid;
  51
  52                 asm volatile("mov %2, %%g1\n\t"
  53                              "mov %3, %%o0\n\t"
  54                              "mov 0 , %%o1\n\t"
  55                              "t 0x6d\n\t"
  56                              "mov %%o1, %0\n\t"
  57                              "mov %%o0, %1" :
  58                              "=r"(in_child), "=r"(child_pid) :
  59                              "i"(__NR_clone), "r"(flags) :
  60                              "%o1", "%o0", "%g1" );
  61
  62                 ret = in_child ? 0 : child_pid;
  63         }
  64 #else
  65         ret = (pid_t) syscall(__NR_clone, flags, NULL);
  66 #endif
  67
  68         if (ret == 0)
  69                 reset_cached_pid();
  70
  71         return ret;
  72 }