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Message-ID: <20170611180158.GS30784@example.net>
Date: Sun, 11 Jun 2017 20:01:58 +0200
From: u-uy74@...ey.se
To: musl@...ts.openwall.com
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); }
fflush(stdout);
_exit(0);
}
-----
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.
Cheers,
Rune
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