GNU bug report logs - #17499
current dfa.c can malloc 0 bytes

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

From: Aharon Robbins <arnold <at> skeeve.com>
To: bug-grep <at> gnu.org
Subject: current dfa.c can malloc 0 bytes
Date: Thu, 15 May 2014 19:22:40 +0300

Hello.

It seems that code in the grep master dfa.c can call xmalloc with
an amount that is zero.  This is OK on GLIBC but is causing some failures
on other systems where malloc(0) fails.

This was not the case a while back (when gawk 4.1.1 was released in
April or so).

It'd be nice if this could be fixed sometime.  To test this in gawk,

Apply the patch below to either master or gawk-4.1-stable from the git repo
and rebuild, and make check.  Gawk 4.1.1 doesn't have this problem.

Thanks

Arnold
---------------
diff --git a/gawkmisc.c b/gawkmisc.c
index a729d88..b07281d 100644
--- a/gawkmisc.c
+++ b/gawkmisc.c
@@ -52,6 +52,8 @@ pointer
 xmalloc(size_t bytes)
 {
 	pointer p;
+	if (bytes == 0)
+		fprintf(stderr, "%s: 0 bytes!\n", __func__), fflush(stderr);
 	emalloc(p, pointer, bytes, "xmalloc");
 	return p;
 }

Message #8 received at 17499 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Aharon Robbins <arnold <at> skeeve.com>, 17499 <at> debbugs.gnu.org
Subject: Re: bug#17499: current dfa.c can malloc 0 bytes
Date: Thu, 15 May 2014 09:48:41 -0700

On 05/15/2014 09:22 AM, Aharon Robbins wrote:
> It seems that code in the grep master dfa.c can call xmalloc with
> an amount that is zero.  This is OK on GLIBC but is causing some failures
> on other systems where malloc(0) fails.

Thanks, I'll try to take a look at this from your recipe.  Are there any 
more details about the failure? What are the symptoms?

A quick look at the dfa.c source code in grep suggests that it can't be 
a direct call to xmalloc, as those args all must be nonzero.  Perhaps 
it's indirect, via xnmalloc or something like that?

Also, gnulib's xmalloc doesn't mind if malloc (0) returns NULL. Is 
gawk's xmalloc pickier?  If so, why?

Message #13 received at 17499-done <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Aharon Robbins <arnold <at> skeeve.com>
Cc: 17499-done <at> debbugs.gnu.org
Subject: Re: bug#17499: current dfa.c can malloc 0 bytes
Date: Thu, 15 May 2014 12:44:25 -0700

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

On 05/15/2014 10:34 AM, Aharon Robbins wrote:
> The wrapper only checks for NULL return.

Ah, thanks, that's the problem then: gawk's xmalloc is pickier than 
grep's, and the extra pickiness is incompatible with what dfa.c 
expects.  I see that gawk's xrealloc is also too picky, but gawk's 
xcalloc is OK.  Attached isa patch to gawk.  As this problem does not 
affect grep I'll close the grep bug.

[0001-Port-to-systems-where-malloc-0-and-or-realloc-P-0-re.patch (text/x-patch, attachment)]

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