Subject: Re: bug#29151: [PATCH] ia64: fix crash in thread context switch
From: [email-masked] (Ludovic Courtès)
To: Sergei Trofimovich <[email-masked]>
Cc: [email-masked]
Date: Wed, 22 Nov 2017 16:16:17 +0100
List-Id: <debbugs-submit.debbugs.gnu.org>

Hi Sergei,

Sergei Trofimovich <[email-masked]> skribis:

> Backtrace looks like that:
>
>   Program terminated with signal SIGSEGV, Segmentation fault.
>   #0  0x200000000014a5c0 in scm_ia64_longjmp (JB=0x6000000000817020, VAL=1) at continuations.c:372
>   372                   t->pending_rbs_continuation->backing_store,
>   [Current thread is 1 (Thread 0x2000000000049340 (LWP 8190))]
>   (gdb) bt
>   #0  0x200000000014a5c0 in scm_ia64_longjmp (JB=0x6000000000817020, VAL=1) at continuations.c:372
>   #1  0x2000000000148e00 in scm_c_abort (vm=0x60000000000edea0, tag=0x6000000000795ba0, n=0, argv=0x60000fffff7f0ce0, cookie=-1) at control.c:239
>   #2  0x2000000000149070 in scm_at_abort (tag=0x6000000000795ba0, args=0x304) at control.c:258
>   (gdb) print t
>   $2 = (scm_i_thread *) 0x6000000000068000
>   (gdb) print t->pending_rbs_continuation
>   $3 = (scm_t_contregs *) 0xffeb
>
> The problem here is the value of 't->pending_rbs_continuation' pointer.
> It's supposed to poin to a register stack pointer or be NULL if not yet
> backed up.
>
> The problem is it is never initialized to NULL at creation time and
> contained garbage on stack. Sometimes people are lucky and have zeros
> on stack and guile works. But sometimes there is something and guile
> crashes.
>
> The fix is trivial: initialize 'pending_rbs_continuation = NULL'
> at thread registration time (the same way other threads are registered).
>
> Reported-by: Matt Turner
> Bug: https://bugs.gentoo.org/613986
>
> * libguile/threads.c(guilify_self_1): initialize pending_rbs_continuation
>   to avoid guile crash on ia64.

I’ve applied the patch to the ‘stable-2.2’ branch, thank you, and thanks
to Jason for testing!

Ludo’.