GNU bug report logs - #21004
25.0.50; Questionable call to getrlimit in handle_sigsegv

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

From: Ken Brown <kbrown <at> cornell.edu>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.0.50; Questionable call to getrlimit in handle_sigsegv
Date: Tue, 07 Jul 2015 16:11:53 -0400

There is a call to setrlimit in main() that tries to increase the stack
size.  As a result of this, the value of rlim.rlim_cur in
handle_sigsegv() might exceed the actual stack size.  See Corinna
Vinschen's message at

  https://www.cygwin.com/ml/cygwin/2015-07/msg00092.html

for a more detailed explanation.

Corinna suggests using pthread_getattr_np instead of getrlimit to avoid
this problem, as in the following patch:

diff --git a/src/sysdep.c b/src/sysdep.c
index 91036f0..c49e333 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -1625,6 +1625,8 @@ handle_arith_signal (int sig)

#ifdef HAVE_STACK_OVERFLOW_HANDLING

+#include <pthread.h>
+
/* -1 if stack grows down as expected on most OS/ABI variants, 1 
otherwise.  */

static int stack_direction;
@@ -1642,9 +1644,11 @@ handle_sigsegv (int sig, siginfo_t *siginfo, void 
*arg)
too nested calls to mark_object.  No way to survive.  */
if (!gc_in_progress)
{
-      struct rlimit rlim;
+      pthread_attr_t attr;
+      size_t stacksize;

-      if (!getrlimit (RLIMIT_STACK, &rlim))
+      if (!pthread_getattr_np (pthread_self (), &attr)
+         && !pthread_attr_getstacksize (&attr, &stacksize))
{
/* STACK_DANGER_ZONE has to be bigger than 16K on Cygwin, for
reasons explained in
@@ -1657,7 +1661,7 @@ handle_sigsegv (int sig, siginfo_t *siginfo, void 
*arg)
char *beg, *end, *addr;

beg = stack_bottom;
-         end = stack_bottom + stack_direction * rlim.rlim_cur;
+         end = stack_bottom + stack_direction * stacksize;
if (beg > end)
addr = beg, beg = end, end = addr;
addr = (char *) siginfo->si_addr;

Of course, the definition of HAVE_STACK_OVERFLOW_HANDLING would have to
be changed to ensure that pthread_getattr_np exists.

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Message #8 received at 21004 <at> debbugs.gnu.org (full text, mbox):

From: Wolfgang Jenkner <wjenkner <at> inode.at>
To: Ken Brown <kbrown <at> cornell.edu>
Cc: 21004 <at> debbugs.gnu.org
Subject: Re: bug#21004: 25.0.50;
 Questionable call to getrlimit in handle_sigsegv
Date: Wed, 08 Jul 2015 15:33:58 +0200

On Tue, Jul 07 2015, Ken Brown wrote:

> Of course, the definition of HAVE_STACK_OVERFLOW_HANDLING would have to
> be changed to ensure that pthread_getattr_np exists.

Other systems may have this under a different name (e.g., FreeBSD has
pthread_attr_get_np and needs to include pthread_np.h).  By the way,
Guile has already some code to deal with this.

Message #11 received at 21004 <at> debbugs.gnu.org (full text, mbox):

From: Ken Brown <kbrown <at> cornell.edu>
To: Wolfgang Jenkner <wjenkner <at> inode.at>
Cc: Dmitry Antipov <dmantipov <at> yandex.ru>, 21004 <at> debbugs.gnu.org
Subject: Re: bug#21004: 25.0.50;
 Questionable call to getrlimit in handle_sigsegv
Date: Wed, 08 Jul 2015 10:20:56 -0400

On 7/8/2015 9:33 AM, Wolfgang Jenkner wrote:
> On Tue, Jul 07 2015, Ken Brown wrote:
>
>> Of course, the definition of HAVE_STACK_OVERFLOW_HANDLING would have to
>> be changed to ensure that pthread_getattr_np exists.
>
> Other systems may have this under a different name (e.g., FreeBSD has
> pthread_attr_get_np and needs to include pthread_np.h).  By the way,
> Guile has already some code to deal with this.

So someone (Dmitry?) would have to do some work to make this more 
portable.  It may or may not be worth the trouble; I'm not even sure yet 
that recovery from stack overflow actually works (see bug#20996).

Ken

Message #14 received at 21004 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Ken Brown <kbrown <at> cornell.edu>
Cc: Corinna Vinschen <corinna-cygwin <at> cygwin.com>, Eli Zaretskii <eliz <at> gnu.org>,
 Wolfgang Jenkner <wjenkner <at> inode.at>, Dmitry Antipov <dmantipov <at> yandex.ru>,
 21004 <at> debbugs.gnu.org
Subject: Re: 25.0.50; Questionable call to getrlimit in handle_sigsegv
Date: Thu, 16 Jul 2015 00:58:10 -0700

[Message part 1 (text/plain, inline)]

Ken, thanks for reporting the problem in <http://bugs.gnu.org/21004>.  Please 
try the attached patch.  Although it avoids getrlimit and it works for me on 
both GNU/Linux and Solaris, I can't easily test it on Cygwin.  I'll CC: this to 
Eli as a heads-up, as he's interested in the MS-Windows case.

[0001-Better-heuristic-for-C-stack-overflow.patch (text/x-diff, attachment)]

Message #19 received at 21004 <at> debbugs.gnu.org (full text, mbox):

From: Ken Brown <kbrown <at> cornell.edu>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: Corinna Vinschen <corinna-cygwin <at> cygwin.com>, Eli Zaretskii <eliz <at> gnu.org>,
 Wolfgang Jenkner <wjenkner <at> inode.at>, Dmitry Antipov <dmantipov <at> yandex.ru>,
 21004 <at> debbugs.gnu.org
Subject: Re: 25.0.50; Questionable call to getrlimit in handle_sigsegv
Date: Thu, 16 Jul 2015 08:15:45 -0400

On 7/16/2015 3:58 AM, Paul Eggert wrote:
> Ken, thanks for reporting the problem in <http://bugs.gnu.org/21004>.  Please
> try the attached patch.  Although it avoids getrlimit and it works for me on
> both GNU/Linux and Solaris, I can't easily test it on Cygwin.  I'll CC: this to
> Eli as a heads-up, as he's interested in the MS-Windows case.

It works on Cygwin.  Thanks.

Ken

Message #22 received at 21004 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: corinna-cygwin <at> cygwin.com, wjenkner <at> inode.at, dmantipov <at> yandex.ru,
 21004 <at> debbugs.gnu.org, kbrown <at> cornell.edu
Subject: Re: 25.0.50; Questionable call to getrlimit in handle_sigsegv
Date: Thu, 16 Jul 2015 17:34:03 +0300

> Date: Thu, 16 Jul 2015 00:58:10 -0700
> From: Paul Eggert <eggert <at> cs.ucla.edu>
> CC: 21004 <at> debbugs.gnu.org, Eli Zaretskii <eliz <at> gnu.org>, 
>  Wolfgang Jenkner <wjenkner <at> inode.at>,
>  Dmitry Antipov <dmantipov <at> yandex.ru>, 
>  Corinna Vinschen <corinna-cygwin <at> cygwin.com>
> 
> Ken, thanks for reporting the problem in <http://bugs.gnu.org/21004>.  Please 
> try the attached patch.  Although it avoids getrlimit and it works for me on 
> both GNU/Linux and Solaris, I can't easily test it on Cygwin.  I'll CC: this to 
> Eli as a heads-up, as he's interested in the MS-Windows case.

Thanks.  The native MS-Windows build doesn't (yet) support
stack-overflow recovery, so the affected code is not compiled into
that build.

Message #27 received at 21004-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: wjenkner <at> inode.at, dmantipov <at> yandex.ru, 21004-done <at> debbugs.gnu.org,
 kbrown <at> cornell.edu
Subject: Re: 25.0.50; Questionable call to getrlimit in handle_sigsegv
Date: Thu, 16 Jul 2015 07:38:18 -0700

Thanks, Ken and Eli, for the quick responses.  I've installed the patch as 
master commit a5522abbca2235771384949dfa87c8efc68831b2 and am closing the bug.

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