On 2023-12-01 10:40, Bruno Haible wrote:
> Indeed, this sentence appears to forbid ((char *) NULL) + something.
Yes. However, Gnulib code can still use ((char *) NULL) + something)
because the Gnulib portability guidelines allow it.
The issue with clang false positives is covered here:
https://www.gnu.org/software/gnulib/manual/html_node/Unsupported-Platforms.html
which lists "clang -fsanitize=undefined" as an unsupported platform
unless you also specify "-fno-sanitize=pointer-overflow".
The obstack patch you installed is fine, as it's clearer and just as
fast as the original. However, we needn't go through Gnulib and change
other code merely because it runs afoul of this false alarm from clang.
It may not be a false alarm in future versions of the compiler. At any time, the compiler may decide to replace ((char *) NULL + 0) by __builtin_unreachable. It can make sense to find an ISO C-compliant replacement of this idiom at some point.