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

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#21004: closed (25.0.50; Questionable call to getrlimit in
 handle_sigsegv)
Date: Thu, 16 Jul 2015 14:39:02 +0000

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Your message dated Thu, 16 Jul 2015 07:38:18 -0700
with message-id <55A7C1DA.3090006 <at> cs.ucla.edu>
and subject line Re: 25.0.50; Questionable call to getrlimit in handle_sigsegv
has caused the debbugs.gnu.org bug report #21004,
regarding 25.0.50; Questionable call to getrlimit in handle_sigsegv
to be marked as done.

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help-debbugs <at> gnu.org.)


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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 part 3 (message/rfc822, inline)]

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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