On Thu, May 27, 2021 at 5:15 PM Hyeonggon Yoo <42.hyeyoo@gmail.com> 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;
Hyeonggon, there is a patch series from Arnd Bergmann, a well-known kernel developer and janitor, hanging around here: https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground.git/log/?h=w... It includes a patch to address this issue: https://git.kernel.org/pub/scm/linux/kernel/git/arnd/playground.git/commit/?... The patch title and commit message indicates that this was submitted in multiple versions to the mailing list. You can find more on its progress on the mailing list here: https://lore.kernel.org/lkml/?q=seq_file%3A+fix+clang+warning+for+NULL+point... It seems that it has not landed in linux-next yet, though: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=... The commit and discussion around it will give you much more technical details on the issue and its resolution. I hope this helps. Lukas