Line data    Source code

       1             : /* SPDX-License-Identifier: LGPL-2.1+ */
       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           2 : static inline pid_t raw_clone(unsigned long flags) {
      32             :         pid_t ret;
      33             : 
      34           2 :         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           2 :         ret = (pid_t) syscall(__NR_clone, flags, NULL);
      73             : #endif
      74             : 
      75           2 :         if (ret == 0)
      76           0 :                 reset_cached_pid();
      77             : 
      78           2 :         return ret;
      79             : }