[Bug sanitizer/99190] New: Undefined behaviour in libubsan

[Bug sanitizer/99190] New: Undefined behaviour in libubsan

[zeccav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

            Bug ID: 99190
           Summary: Undefined behaviour in libubsan
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zeccav at gmail dot com
                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, marxin at gcc dot gnu.org
  Target Milestone: ---

// gcc -fsanitize=shift -w
// ldd a.out produces
// libubsan.so.1 => /home/vitti/local/gcc-150221-undefined/lib64/libubsan.so.1
// ./a.out produces
// ../../../../gcc-150221/libsanitizer/ubsan/ubsan_value.cpp:77:25: runtime
error: left shift of 0x0000000000000000fffffffffffffffb by 96 places cannot be
represented in type '__int128'
// ubsan_value.cpp:77 -> "return SIntMax(Val) << ExtraBits >> ExtraBits;"
int main (void)
{

  1 << -5;

  return 0;
}

[Bug sanitizer/99190] Undefined behaviour in libubsan

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
It is UB only in C++17 or earlier, so one way to "fix" it is build libubsan
with -std=gnu++20.
Or the SIntMax(Val) << ExtraBits >> ExtraBits can be replaced by
SIntMax(UIntMax(Val) << ExtraBits) >> ExtraBits.

[Bug sanitizer/99190] Undefined behaviour in libubsan

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2021-02-22
           Assignee|unassigned at gcc dot gnu.org      |marxin at gcc dot gnu.org

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
I'll handle it.

[Bug sanitizer/99190] Undefined behaviour in libubsan

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Interesting, you are searching for UBSAN in libsanitizer.
Can you please share details how do you build libubsan with -fsanitize=shift?

[Bug sanitizer/99190] Undefined behaviour in libubsan

[zeccav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

--- Comment #4 from Vittorio Zecca <zeccav at gmail dot com> ---
To generate a sanitized version of libgfortran I built whole sanitized
gcc with the following command:

CFLAGS="-g -O0 -fsanitize=undefined -lubsan" LIBS="-lubsan"
CXXFLAGS=$CFLAGS ../gcc-150221/configure
--prefix=/home/vitti/local/gcc-150221-undefined
--enable-languages=c,c++,fortran --disable-multilib --disable-lto
--disable-plugin
--disable-bootstrap

But I remember I had to tweak the build here and there.
It is not trivial.

[Bug sanitizer/99190] Undefined behaviour in libubsan

[zeccav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

--- Comment #5 from Vittorio Zecca <zeccav at gmail dot com> ---
Sorry I meant libubsan, but I am building the whole gcc, g++, and gfortran
sanitized version.

[Bug sanitizer/99190] Undefined behaviour in libubsan

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |https://reviews.llvm.org/D9
                   |                            |7263

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
I can reproduce it and I've just made an upstream pull request:
https://reviews.llvm.org/D97263

[Bug sanitizer/99190] Undefined behaviour in libubsan

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #7 from Martin Liška <marxin at gcc dot gnu.org> ---
Fixed in master with g:e03e58c1844d04678f95b278f3eff2a5fbaeff75.

[Bug sanitizer/99190] Undefined behaviour in libubsan

[zeccav at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99190

--- Comment #8 from Vittorio Zecca <zeccav at gmail dot com> ---
I can confirm the new libubsan works on my test case.

Keep up the good work!