GNU bug report logs - #30394
'posix_spawn' glibc 2.26 race condition fires under qemu-binfmt

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Danny Milosavljevic <dannym <at> scratchpost.org>
To: ng0 <at> n0.is, guix-devel <at> gnu.org, <bug-guix <at> gnu.org>
Subject: ARM compilation via qemu binfmt - Assertion failure
Date: Thu, 8 Feb 2018 17:42:38 +0100

Hi ng0,

On Tue, 06 Feb 2018 10:33:56 +0000
ng0 <at> n0.is wrote:

> recently I've read about slow but native compiling of ARM on qemu.

Unfortunately, there's a (pretty reproducible) problem with it.

guix-master/guix $ ./pre-inst-env guix system disk-image --system=armhf-linux -e "(@ (gnu system install) installation-os)"
[... building grub-2.02 ...]
phase `configure' succeeded after 821.8 seconds
starting phase `patch-generated-file-shebangs'
patch-makefile-SHELL: ./po/Makefile: changing `SHELL' from `/bin/sh' to `/gnu/st[...]
phase `patch-generated-file-shebangs' succeeded after 14.6 seconds
starting phase `build'
bison -d -p grub_script_yy -b grub_script ./grub-core/script/parser.y
flex -o grub_script.yy.c --header-file=grub_script.yy.h ./grub-core/script/yylex[...]
bison: ../sysdeps/unix/sysv/linux/spawni.c:360: __spawnix: Assertion `ec >= 0' failed

This is only fixed in glibc 2.27 (not in core-updates).

The fix is:

https://sourceware.org/bugzilla/show_bug.cgi?id=22273
diff --git a/sysdeps/unix/sysv/linux/spawni.c b/sysdeps/unix/sysv/linux/spawni.c
index dea1650..f02ac19 100644
--- a/sysdeps/unix/sysv/linux/spawni.c
+++ b/sysdeps/unix/sysv/linux/spawni.c
@@ -365,9 +365,15 @@ __spawnix (pid_t * pid, const char *file,
   if (new_pid > 0)
     {
       ec = args.err;
-      assert (ec >= 0);
       if (ec != 0)
-         __waitpid (new_pid, NULL, 0);
+       {
+         /* It handles the unlikely case where the auxiliary vfork process
+            is killed before calling _exit or execve.  */
+         int status;
+         __waitpid (new_pid, &status, 0);
+         if (WIFSIGNALED (status))
+           ec = 0;
+       }
     }
   else
     ec = -new_pid;

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