Re: undefined-behavior obstack.c:139

[Paul Eggert]

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.