[Bug sanitizer/115273] New: [12 Regression] passing zero to ctz() check missing

[Bug sanitizer/115273] New: [12 Regression] passing zero to ctz() check missing

[bic60176 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115273

            Bug ID: 115273
           Summary: [12 Regression] passing zero to ctz() check missing
           Product: gcc
           Version: 12.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bic60176 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
  Target Milestone: ---

Created attachment 58305
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58305&action=edit
testcase

OS: Ubuntu 22.04.3 LTS
We found a case that UBSAN missed checking if zero is passed to __builtin_ctz()
when compiling with gcc-12.3.0.
When compiling with gcc-11.4.0, gcc-13.2.0, and gcc-14.1.0, UBSAN can detect
the undefined behavior.

$ ../compiler-builds/gcc-12.3.0_build/bin/gcc -fsanitize=undefined -g -lgcc_s
-I/home/csmith/include/csmith-2.3.0 testcase.c -o exec

$ timeout 1s ./exec 2>exec.err

$ cat exec.err

$ ../compiler-builds/gcc-11.4.0_build/bin/gcc -fsanitize=undefined -g -lgcc_s
-I/home/csmith/include/csmith-2.3.0 testcase.c -o exec

$ timeout 1s ./exec 2>exec.err
testcase.c:957:44: runtime error: passing zero to ctz(), which is not a valid
argument testcase.c:997:25: runtime error: passing zero to ctz(), which is not
a valid argument testcase.c:957: runtime error: passing zero to ctz(), which is
not a valid argument testcase.c:997: runtime error: passing zero to ctz(),
which is not a valid argument testcase.c:957: runtime error: passing zero to
ctz(), which is not a valid argument testcase.c:997: runtime error: passing
zero to ctz(), which is not a valid argument testcase.c:957: runtime error:
passing zero to ctz(), which is not a valid argument testcase.c:997: runtime
error: passing zero to ctz(), which is not a valid argument testcase.c:957:
runtime error: passing zero to ctz(), which is not a valid argument
testcase.c:997: runtime error: passing zero to ctz(), which is not a valid
argument testcase.c:957: runtime error: passing zero to ctz(), which is not a
valid argument testcase.c:997: runtime error: passing zero to ctz(), which is
not a valid argument testcase.c:957: runtime error: passing zero to ctz(),
which is not a valid argument testcase.c:997: runtime error: passing zero to
ctz(), which is not a valid argument testcase.c:957: runtime error: passing
zero to ctz(), which is not a valid argument testcase.c:997: runtime error:
passing zero to ctz(), which is not a valid argument testcase.c:957: runtime
error: passing zero to ctz(), which is not a valid argument testcase.c:997:
runtime error: passing zero to ctz(), which is not a valid argument
testcase.c:957: runtime error: passing zero to ctz(), which is not a valid
argument testcase.c:997: runtime error: passing zero to ctz(), which is not a
valid argument

[Bug sanitizer/115273] [12 Regression] passing zero to ctz() check missing

[bic60176 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115273

--- Comment #1 from Bi6c <bic60176 at gmail dot com> ---
Created attachment 58306
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58306&action=edit
preprocessed file

[Bug sanitizer/115273] [12 Regression] passing zero to ctz() check missing

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115273

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |12.4

[Bug sanitizer/115273] [12 Regression] passing zero to ctz() check missing

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115273

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase:
```
int f(int a)
{
        return __builtin_ctz(a) == 0;
}

int main(void)
{
        __builtin_printf("%d\n", f(0));
}
```

[Bug sanitizer/115273] [12 Regression] passing zero to ctz() check missing

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115273

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup.

*** This bug has been marked as a duplicate of bug 115127 ***

[Bug sanitizer/115273] [12 Regression] passing zero to ctz() check missing

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115273

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note ubsan can detect (correctly) a different undefined behavior since GCC 13
(since r13-4988-g8692b15ae7c05e; aka PR108256) but the undefinedness of passing
0 to ctz is still not detected and that is a dup of bug 115127 .