Description of problem:
while building git with:
it will abort (it uses -Werror) while trying to build dir.c with the following message:
dir.c: In function ‘git_url_basename’:
dir.c:3085:13: error: ‘memchr’ specified bound [9223372036854775808, 0] exceeds maximum object size 9223372036854775807 [-Werror=stringop-overread]
3085 | if (memchr(start, '/', end - start) == NULL
the issue is triggered with -O2 or higher in that codebase, but hadn't been able to generate a minimized reproducer.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. get git sources (either from a release or git)
2. make DEVELOPER=1 dir.o
DEVELOPER=1 is used by git's CI which is likely to break with fc36 release, presume the fc36 package is showing the warning but has been ignored, hence fc36 will have a working git package
this has been reported in Debian as well, but couldn't find an upstreamed bug and don't have an account there (yet) to create one, if that would be preferred.
AFAIK, the issue might had even manifested itself with -O3 in a previous gcc version
based on additional investigation from the Windows Git maintainer this might seem to be related to a known issue in gcc which is labeled as WONTFIX.
The two problems are unrelated. The one here is due to GCC being overly conservative about the results of pointer subtraction, or more generally, not having the "smarts" to know that result of incrementing a pointer to an object is necessarily greater than or equal to the object's address. For example, in the snippet below it's safe to assume that the condition is true (otherwise the program would be undefined), and eliminate the call to abort(). Because GCC doesn't do that, conditions like that hamper subsequent optimizations that in turn sometimes trigger false positive warnings.
void f (int n)
char a, *p = a + n;
if (p < a)
Possible sighting in OpenJDK: