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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/109050] New: UBsan failed to detect out-of-bound at
 -O0/1/2/s
Date: Tue, 07 Mar 2023 08:51:53 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: sanitizer
X-Bugzilla-Version: 13.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109050

            Bug ID: 109050
           Summary: UBsan failed to detect out-of-bound at -O0/1/2/s
           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, UBsan failed to detect the out-of-bound access at a=
ll
opt levels. Clang can detect it at all opt levels.

Compiler explorer: https://godbolt.org/z/TK35hvPrK

% cat a.c
long a;
int b;
int main() {
  int c[4]=3D{0, 1, 2, 3};
  a =3D 0;
  for (; a <=3D 2; a++)
    c[a - 9806816] |=3D b;
}
%
% gcc-tk -O0 -fsanitize=3Dundefined a.c && ./a.out
%
% gcc-tk -O1 -fsanitize=3Dundefined a.c && ./a.out
%
% clang -O1 -fsanitize=3Dundefined a.c && ./a.out
/a.c:7:5: runtime error: index -9806816 out of bounds for type 'int[4]'
...
% gcc-tk -v
Using built-in specs.
COLLECT_GCC=3Dgcc-tk
COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-7e9dd=
9de169034810b92d47bf78284db731fa5da/libexec/gcc/x86_64-pc-linux-gnu/13.0.1/=
lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=3Dc,c++
--prefix=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-7e9dd9de16903481=
0b92d47bf78284db731fa5da
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.1 20230221 (experimental) (GCC)
%=