Re: Performing pointer arithmetic on a null pointer?

On Fri, May 28, 2021 at 12:14:43AM +0900, Hyeonggon Yoo wrote:

Hello, I was compiling kernel with make CC=clang-10 W=1 -s

there are some places that compiler complains about pointer arithmetic like below.it says it's undefined behavior.

is it just OK to use UBs like this (I hope it's not), or am I missing something?

fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on a null pointer has undefined behavior [-Wnull-pointer-arithmetic] return NULL + !*ppos;

Should work just fine, what problems have you found with that code? Also happens in a few other places in the vfs layer. Tricky code, but it works as pointer math is valid C code :) thanks, greg k-h