On Sat, Jan 16, 2021 at 2:59 AM Eric Biggers <ebigg...@kernel.org> wrote:
> On Sat, Jan 16, 2021 at 08:59:50AM +0800, kernel test robot wrote
>
> Looks like the clang bug that causes large stack usage in this function
> (https://bugs.llvm.org/show_bug.cgi?id=45803 which is still unfixed) got
> triggered again. Note that the function only has 264 bytes of local
> variables,
> so there's no reason why it should use anywhere near 9776 bytes of stack
> space.
>
> I'm not sure what we can do about this. Last time the solution was commit
> 0c0408e86dbe which randomly added a 'pragma nounroll' to the loop at the end.
>
> Anyone have any better idea than randomly trying adding optimization pragmas
> and
> seeing what makes the report go away?
>
> Also this was reported with clang 12.0.0 which is a prerelease version, so I'm
> not sure how much I'm supposed to care about this report.
I sent a workaround to disable UBSAN_UNSIGNED_OVERFLOW an
x86-32, after showing that this did not affect arm32, arm64 or x86-64:
27c287b41659 ("ubsan: disable unsigned-overflow check for i386")
As the report is for ppc64, it appears that this is not just specific to x86-32
after all. I have had no success in isolating the problem in clang, but I
did not try too hard either. I see this .config also enables
CONFIG_UBSAN_UNSIGNED_OVERFLOW=y, so it would be a
reasonable assumption that this is the same problem as on x86-32.
There is also another thread on CONFIG_UBSAN_UNSIGNED_OVERFLOW
causing BUILD_BUG_ON() failures.
Arnd
