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Date: Sun, 11 Jun 2017 20:01:58 +0200
Subject: more fun with non-Linux Linux ABI

FWIIW: when running under Linux ABI on FreeBSD
in musl-linked programs the child processes segfault right after a
vfork(), before doing anything else:

#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/wait.h>

int main( int argc, char **argv ) {
  int s;
  pid_t pid = vfork();
  if( !pid ){ _exit(0); }
  else      { wait(&s); printf("vfork() = %d\n", pid); }
 50124 ktrace   RET   ktrace 0
 50124 ktrace   CALL  execve(0x7fffffffee4b,0x7fffffffec38,0x7fffffffec48)
 50124 ktrace   NAMI  "./v"
 50124 v        RET   linux_olduname 0
 50124 v        CALL  linux_set_thread_area(0xffffcc6c)
 50124 v        RET   linux_set_thread_area 0
 50124 v        CALL  linux_set_tid_address(0x804d524)
 50124 v        RET   linux_set_tid_address 50124/0xc3cc
 50124 v        CALL  linux_vfork
 50124 v        RET   linux_vfork 50125/0xc3cd
 50125 v        RET   linux_fork 0
 50125 v        PSIG  SIGSEGV SIG_DFL code=SEGV_MAPERR
 50125 v        NAMI  "v.core"
 50124 v        CALL  linux_wait4(0xffffffff,0xffffcd4c,0,0)
 50124 v        RET   linux_wait4 50125/0xc3cd
 50124 v        CALL  linux_ioctl(0x1,0x5413,0xffffcb04)
 50124 v        RET   linux_ioctl 0
 50124 v        CALL  linux_writev(0x1,0xffffcad4,0x2)
 50124 v        GIO   fd 1 wrote 16 bytes
       "vfork() = 50125
 50124 v        RET   linux_writev 16/0x10
 50124 v        CALL  linux_exit_group(0)

Remarkably this apparently does not affect glibc-based builds
(I have not tested right now but otherwise it would have been known).
Wonder what makes the difference.

Otherwise a simple workaround would be an option to make vfork()
a fork() synonym while building musl. (I do the this at applications
build time instead, which helps.)

Such an option would most probably result in a pretty small performance
impact on modern (native) Linux.


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