From: Jakub Jelinek <jakub@redhat.com>
To: Kyle Moffett <mrmacman_g4@mac.com>
Cc: Paulo Marques <pmarques@grupopie.com>,
Shankar Unni <shankarunni@netscape.net>,
akpm@osdl.org, linux-kernel@vger.kernel.org, bunk@stusta.de,
khali@linux-fr.org
Subject: Not a GCC bug (was Re: Big GCC bug!!! [Was: Re: Do not misuse Coverity please])
Date: Wed, 30 Mar 2005 18:38:25 -0500 [thread overview]
Message-ID: <20050330233825.GS17420@devserv.devel.redhat.com> (raw)
In-Reply-To: <aae129062f1e3992c8ec025d5f239be9@mac.com>
On Wed, Mar 30, 2005 at 06:11:43PM -0500, Kyle Moffett wrote:
> On Mar 30, 2005, at 14:14, Paulo Marques wrote:
> >Just a minor nitpick, though: wouldn't it be possible for an
> >application to catch the SIGSEGV and let the code proceed,
> >making invalid the assumption made by gcc?
>
> Uhh, it's even worse than that. Have a look at the following code:
> >#include <stdio.h>
> >#include <stdlib.h>
> >#include <string.h>
> >#include <errno.h>
> >#include <sys/types.h>
> >#include <sys/mman.h>
> >
> >struct test {
> > int code;
> >};
> >int test_check_first(struct test *a) {
> > int ret;
> > if (!a) return -1;
> > ret = a->code;
> > return ret;
> >}
> >int test_check_last(struct test *a) {
> > int ret;
> > ret = a->code;
> > if (!a) return -1;
> > return ret;
> >}
> >
> >int main() {
> > int i;
> > struct test *nullmem = mmap(NULL, 4096, PROT_READ|PROT_WRITE,
> > MAP_ANON|MAP_FIXED|MAP_PRIVATE, -1, 0);
> > if (nullmem == MAP_FAILED) {
> > fprintf(stderr,"mmap: %s\n",strerror(errno));
> > exit(1);
> > }
> > for (i = 0; i < 2; i++) {
> > nullmem[i].code = i;
> > printf("nullmem[%d].code = %d\n",i,i);
> > printf("test_check_first(&nullmem[%d]) = %d\n",i,
> > test_check_first(&nullmem[i]));
> > printf("test_check_last(&nullmem[%d]) = %d\n",i,
> > test_check_last(&nullmem[i]));
> > }
> > munmap(nullmem,4096);
> > exit(0);
> >}
This testcase violates ISO C99 6.3.2.3:
If a null pointer constant is converted to a pointer type, the resulting
pointer, called a null pointer, is guaranteed to compare unequal to a
pointer to any object or function.
But in the testcase above, there is an object whose pointer compares equal
to the null pointer. So there is nothing wrong with what GCC does.
Jakub
next prev parent reply other threads:[~2005-03-30 23:40 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-03-27 20:50 [2.6 patch] sound/oss/cs46xx.c: fix a check after use Adrian Bunk
2005-03-27 21:21 ` Do not misuse Coverity please (Was: sound/oss/cs46xx.c: fix a check after use) Jean Delvare
2005-03-27 21:43 ` Adrian Bunk
2005-03-27 22:34 ` Jean Delvare
2005-03-27 22:45 ` Russell King
2005-03-28 12:54 ` Matthias-Christian Ott
2005-03-28 23:57 ` L. A. Walsh
2005-03-29 6:05 ` Daniel Barkalow
2005-03-29 6:23 ` Andrew Morton
2005-03-29 10:46 ` Jean Delvare
2005-03-29 14:12 ` Chris Friesen
2005-03-30 1:25 ` Horst von Brand
2005-03-30 7:53 ` Do not misuse Coverity please Jean Delvare
2005-03-30 17:09 ` Horst von Brand
2005-04-11 20:23 ` Pavel Machek
2005-03-30 18:29 ` Shankar Unni
2005-03-30 18:55 ` Olivier Galibert
2005-03-31 2:01 ` Patrick McFarland
2005-03-30 19:14 ` Paulo Marques
2005-03-30 23:11 ` Big GCC bug!!! [Was: Re: Do not misuse Coverity please] Kyle Moffett
2005-03-30 23:38 ` Jakub Jelinek [this message]
2005-03-31 0:58 ` Not a GCC bug (was Re: Big GCC bug!!! [Was: Re: Do not misuse Coverity please]) Kyle Moffett
2005-03-31 1:12 ` Nick Piggin
2005-03-31 1:27 ` Kyle Moffett
2005-03-29 14:22 ` Do not misuse Coverity please (Was: sound/oss/cs46xx.c: fix a check after use) Daniel Jacobowitz
2005-03-29 22:37 ` Kyle Moffett
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