Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 14 Jun 2021 17:35:45 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     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>,
        Nick Desaulniers <ndesaulniers@google.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@intel.com,
        oberpar@linux.vnet.ibm.com, linux-toolchains@vger.kernel.org
Subject: Re: [PATCH v9] pgo: add clang's Profile Guided Optimization
 infrastructure
Message-ID: <20210614153545.GA68749@worktop.programming.kicks-ass.net>
References: <CAGG=3QXjD1DQjACu=CQQSP=whue-14Pw8FcNcXrJZfLC_E+y9w@mail.gmail.com>
 <YMT5xZsZMX0PpDKQ@hirez.programming.kicks-ass.net>
 <CAGG=3QVHkkJ236mCJ8Jt_6JtgYtWHV9b4aVXnoj6ypc7GOnc0A@mail.gmail.com>
 <20210612202505.GG68208@worktop.programming.kicks-ass.net>
 <CAGG=3QUZ9tXGNLhbOr+AFDTJABDujZuaG1mYaLKdTcJZguEDWw@mail.gmail.com>
 <YMca2aa+t+3VrpN9@hirez.programming.kicks-ass.net>
 <CAGG=3QVPCuAx9UMTOzQp+8MJk8KVyOfaYeV0yehpVwbCaYMVpg@mail.gmail.com>
 <YMczJGPsxSWNgJMG@hirez.programming.kicks-ass.net>
 <CANpmjNNnZv7DHYaJBL7knn9P+50F+SOCvis==Utaf-avENnVsw@mail.gmail.com>
 <202106140817.F584D2F@keescook>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <202106140817.F584D2F@keescook>
Precedence: bulk

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.