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

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Message-ID: <202012041643.CB4EEED17@keescook>
Date:   Fri, 4 Dec 2020 16:46:16 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        George Popescu <georgepope@...roid.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 5/7] ubsan: Enable for all*config builds

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@...omium.org> 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@mail.gmail.com/
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> 
> 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