src/basic/raw-clone.h

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 #pragma once
   3
   4 /***
   5   Copyright 2010 Lennart Poettering
   6   Copyright 2016 Michael Karcher
   7 ***/
   8
   9 #include <errno.h>
  10 #include <sched.h>
  11 #include <sys/syscall.h>
  12
  13 #include "log.h"
  14 #include "macro.h"
  15
  16 /**
  17  * raw_clone() - uses clone to create a new process with clone flags
  18  * @flags: Flags to pass to the clone system call
  19  *
  20  * Uses the clone system call to create a new process with the cloning flags and termination signal passed in the flags
  21  * parameter. Opposed to glibc's clone funtion, using this function does not set up a separate stack for the child, but
  22  * relies on copy-on-write semantics on the one stack at a common virtual address, just as fork does.
  23  *
  24  * To obtain copy-on-write semantics, flags must not contain CLONE_VM, and thus CLONE_THREAD and CLONE_SIGHAND (which
  25  * require CLONE_VM) are not usable.
  26  *
  27  * Additionally, as this function does not pass the ptid, newtls and ctid parameters to the kernel, flags must not
  28  * contain CLONE_PARENT_SETTID, CLONE_CHILD_SETTID, CLONE_CHILD_CLEARTID or CLONE_SETTLS.
  29  *
  30  * Returns: 0 in the child process and the child process id in the parent.
  31  */
  32 static inline pid_t raw_clone(unsigned long flags) {
  33         pid_t ret;
  34
  35         assert((flags & (CLONE_VM|CLONE_PARENT_SETTID|CLONE_CHILD_SETTID|
  36                          CLONE_CHILD_CLEARTID|CLONE_SETTLS)) == 0);
  37 #if defined(__s390x__) || defined(__s390__) || defined(__CRIS__)
  38         /* On s390/s390x and cris the order of the first and second arguments
  39          * of the raw clone() system call is reversed. */
  40         ret = (pid_t) syscall(__NR_clone, NULL, flags);
  41 #elif defined(__sparc__)
  42         {
  43                 /**
  44                  * sparc always returns the other process id in %o0, and
  45                  * a boolean flag whether this is the child or the parent in
  46                  * %o1. Inline assembly is needed to get the flag returned
  47                  * in %o1.
  48                  */
  49                 int in_child, child_pid, error;
  50
  51                 asm volatile("mov %3, %%g1\n\t"
  52                              "mov %4, %%o0\n\t"
  53                              "mov 0 , %%o1\n\t"
  54 #if defined(__arch64__)
  55                              "t 0x6d\n\t"
  56 #else
  57                              "t 0x10\n\t"
  58 #endif
  59                              "addx %%g0, 0, %2\n\t"
  60                              "mov %%o1, %0\n\t"
  61                              "mov %%o0, %1" :
  62                              "=r"(in_child), "=r"(child_pid), "=r"(error) :
  63                              "i"(__NR_clone), "r"(flags) :
  64                              "%o1", "%o0", "%g1" "cc" );
  65
  66                 if (error) {
  67                         errno = child_pid;
  68                         ret = -1;
  69                 } else
  70                         ret = in_child ? 0 : child_pid;
  71         }
  72 #else
  73         ret = (pid_t) syscall(__NR_clone, flags, NULL);
  74 #endif
  75
  76         if (ret == 0)
  77                 reset_cached_pid();
  78
  79         return ret;
  80 }