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

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Date:   Mon, 14 Jun 2021 11:43:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Bill Wendling <morbo@...gle.com>
Cc:     Kees Cook <keescook@...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>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        andreyknvl@...il.com, dvyukov@...gle.com, elver@...gle.com,
        johannes.berg@...el.com, oberpar@...ux.vnet.ibm.com, mliska@...e.cz
Subject: Re: [PATCH v9] pgo: add clang's Profile Guided Optimization
 infrastructure

On Sun, Jun 13, 2021 at 11:07:26AM -0700, Bill Wendling wrote:

> > > Now, for the "nointr" issue. I'll see if we need an additional change for that.
> > >
> > The GCOV implementation disables profiling in those directories where
> > instrumentation would fail. We do the same. Both clang and gcc seem to
> > treat the no_instrument_function attribute similarly.

Both seem to emit instrumentation, so they're both, simliarly, *broken*.

noinstr *MUST* disable all compiler generated instrumentation. Also see:

  https://lkml.kernel.org/r/20210527194448.3470080-1-elver@google.com

I'll go mark GCOV support as BROKEN for x86.