Bug 97568 - -fanalyzer assumes that an extern const pointer is NULL
Summary: -fanalyzer assumes that an extern const pointer is NULL
Status: RESOLVED FIXED
Alias: None
Product: gcc
Classification: Unclassified
Component: analyzer (show other bugs)
Version: 11.0
: P3 normal
Target Milestone: ---
Assignee: David Malcolm
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-10-25 12:13 UTC by Vincent Lefèvre
Modified: 2020-10-27 14:18 UTC (History)
0 users

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Known to work:
Known to fail:
Last reconfirmed: 2020-10-26 00:00:00

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Description Vincent Lefèvre 2020-10-25 12:13:23 UTC 
On the following program tst.c:

extern int *const s;
int main (void)
{
  return s[0];
}

I get under Debian/unstable:


zira:~> gcc-snapshot -fanalyzer -c tst.c
tst.c: In function 'main':
tst.c:4:11: warning: dereference of NULL '0' [CWE-690] [-Wanalyzer-null-dereference]
    4 |   return s[0];
      |          ~^~~
  'main': event 1
    |
    |

This occurs with:

gcc (Debian 20201023-1) 11.0.0 20201023 (experimental) [master revision d08d481912b:b3da6ca6235:9e3b9ddb996f18d541a3e03611d46c3a6c0c0b5f]

There was no such issue with:

gcc (Debian 20201002-1) 11.0.0 20201002 (experimental) [master revision 05d39f0de9e:767e018251e:1d3e12c469e5f5627c2e271232e1a3d8a88783be]
Comment 1 Vincent Lefèvre 2020-10-26 00:00:22 UTC 
The bug has been introduced by commit af66094d037793773eb8a49597866457f2f6a104.
Comment 2 David Malcolm 2020-10-26 22:14:12 UTC 
Thanks for filing this; confirmed.  I'm working on a fix.
Comment 3 CVS Commits 2020-10-27 13:56:40 UTC 
The master branch has been updated by David Malcolm <dmalcolm@gcc.gnu.org>:

https://gcc.gnu.org/g:16ad9ae85bb5b9acf80f9d1cf2be5a989ef7ba49

commit r11-4437-g16ad9ae85bb5b9acf80f9d1cf2be5a989ef7ba49
Author: David Malcolm <dmalcolm@redhat.com>
Date:   Tue Oct 27 09:54:25 2020 -0400

    analyzer: don't assume extern const vars are zero-initialized [PR97568]
    
    gcc/analyzer/ChangeLog:
            PR analyzer/97568
            * region-model.cc (region_model::get_initial_value_for_global):
            Move check that !DECL_EXTERNAL from here to...
            * region.cc (decl_region::get_svalue_for_initializer): ...here,
            using it to reject zero initialization.
    
    gcc/testsuite/ChangeLog:
            PR analyzer/97568
            * gcc.dg/analyzer/pr97568.c: New test.
Comment 4 David Malcolm 2020-10-27 14:18:34 UTC 
Should be fixed by the above commit.