linux-kernel - Re: [PATCH v9] pgo: add clang's Profile Guided Optimization infrastructure

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Date:   Mon, 14 Jun 2021 13:49:29 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>
Cc:     Marco Elver <elver@...gle.com>, Bill Wendling <morbo@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Johannes Berg <johannes.berg@...el.com>,
        oberpar@...ux.vnet.ibm.com, linux-toolchains@...r.kernel.org,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v9] pgo: add clang's Profile Guided Optimization infrastructure

On Mon, Jun 14, 2021 at 11:07 AM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Mon, Jun 14, 2021 at 9:23 AM Kees Cook <keescook@...omium.org> wrote:
> >
> > On Mon, Jun 14, 2021 at 05:35:45PM +0200, Peter Zijlstra wrote:
> > > On Mon, Jun 14, 2021 at 08:26:01AM -0700, Kees Cook wrote:
> > > > So, AFAICT, the original blocking issue ("PGO does not respect noinstr")
> > > > is not actually an issue (noinstr contains notrace, which IS respected
> > > > by PGO[2]), I think this is fine to move forward.
> > >
> > > It is *NOT*: https://godbolt.org/z/9c7xdvGd9
> > >
> > > Look at how both compilers generate instrumentation in the no_instr()
> > > function.
> >
> > Well that's disappointing. I'll put this on hold until Clang can grow an
> > appropriate attribute (or similar work-around). Thanks for catching
> > that.
>
> Cross referencing since these two threads are related.
> https://lore.kernel.org/lkml/CAKwvOdmPTi93n2L0_yQkrzLdmpxzrOR7zggSzonyaw2PGshApw@mail.gmail.com/

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80223 looked appropriate
to me, so I commented on it.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80223#c6

Patches for:
PGO: https://reviews.llvm.org/D104253
GCOV: https://reviews.llvm.org/D104257
--
Thanks,
~Nick Desaulniers