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From: "shaohua.li at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug sanitizer/107893] New: gcc trunk at -O0 (UBSan) misses a
 Null-pointer-dereference
Date: Mon, 28 Nov 2022 08:40:18 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: sanitizer
X-Bugzilla-Version: 13.0
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X-Bugzilla-Severity: normal
X-Bugzilla-Who: shaohua.li at inf dot ethz.ch
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107893

            Bug ID: 107893
           Summary: gcc trunk at -O0 (UBSan) misses a
                    Null-pointer-dereference
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxi=
n at gcc dot gnu.org
  Target Milestone: ---

For the following code, `gcc-trunk -O0 -fsanitize=3Dundefined=20
-fno-sanitize-recover=3Dall` misses the NULL-pointer-dereference, while
`gcc-trunk -Ox -fsanitize=3Daddress  -fno-sanitize-recover=3Dall` (x=3D1, 2=
, 3, or s)
can detect it.

I checked gcc8/9/10/11/12 and they all have this issue.

clang can detect it at all optimization levels.

Compiler explorer: https://godbolt.org/z/85qfdccse

% cat a.c
int main() {
  int *a =3D 0;
   (a[1] | a[0]) >> 056;
}
%
% gcc-tk -O0 -fsanitize=3Dundefined -fno-sanitize-recover=3Dall -w a.c &&./=
a.out
Segmentation fault
% gcc-tk -O1 -fsanitize=3Dundefined -fno-sanitize-recover=3Dall -w a.c &&./=
a.out
a.c:3:13: runtime error: load of null pointer of type 'int'
%=