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In-Reply-To: <202106140921.5E591BD@keescook>
From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Mon, 14 Jun 2021 11:07:59 -0700
Message-ID: <CAKwvOdkiQCuWB7VrQ4T-OCdoNfqKhpLx_jtBQ_uyjVVwHSOc=A@mail.gmail.com>
Subject: Re: [PATCH v9] pgo: add clang's Profile Guided Optimization infrastructure
To:     Kees Cook <keescook@chromium.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Marco Elver <elver@google.com>,
        Bill Wendling <morbo@google.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Linux Doc Mailing List <linux-doc@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Sami Tolvanen <samitolvanen@google.com>,
        Fangrui Song <maskray@google.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Johannes Berg <johannes.berg@intel.com>,
        oberpar@linux.vnet.ibm.com, linux-toolchains@vger.kernel.org
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On Mon, Jun 14, 2021 at 9:23 AM Kees Cook <keescook@chromium.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/
-- 
Thanks,
~Nick Desaulniers