Re: [PATCH v2 5/7] ubsan: Enable for all*config builds

[Kees Cook]

On Thu, Dec 03, 2020 at 09:51:40AM +0100, Arnd Bergmann wrote:
> On Thu, Dec 3, 2020 at 1:44 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> >
> > With UBSAN_OBJECT_SIZE disabled for GCC, only UBSAN_ALIGNMENT remained
> > a noisy UBSAN option. Disable it for COMPILE_TEST so the rest of UBSAN
> > can be used for full all*config builds or other large combinations.
> >
> > Link: https://lore.kernel.org/lkml/CAHk-=wgXW=YLxGN0QVpp-1w5GDd2pf1W-FqY15poKzoVfik2qA@xxxxxxxxxxxxxx/
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> 
> Have you checked if this has a notable impact on allmodconfig compile speed
> with gcc or clang? I think I've seen significant increases in build times before
> with this, but I don't remember the actual magnitude.
> 
> Making it 20% slower would probably be ok, but making it twice as slow might
> be too much.

For an x86_64 gcc allmodconfig before, I was seeing around 6m2s. After,
I'm seeing around 6m17s, so that's about 8% longer build time.

I will double-check clang...

-- 
Kees Cook