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Date:   Thu, 29 Oct 2020 15:31:13 -0500
From:   Segher Boessenkool <segher@kernel.crashing.org>
To:     Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
        <netdev@vger.kernel.org>,
        "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
        <bpf@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Kees Cook <keescook@chromium.org>,
        linux-toolchains@vger.kernel.org
Subject: Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
Message-ID: <20201029203113.GJ2672@gate.crashing.org>
References: <20201028171506.15682-1-ardb@kernel.org> <20201028171506.15682-2-ardb@kernel.org> <20201028213903.fvdjydadqt6tx765@ast-mbp.dhcp.thefacebook.com> <CAMj1kXFHcM-Jb+MwsLtB4NMUmMyAGGLeNGNLC9vTATot3NJLrA@mail.gmail.com> <20201028225919.6ydy3m2u4p7x3to7@ast-mbp.dhcp.thefacebook.com> <CAMj1kXG8PmvO6bLhGXPWtzKMnAsip2WDa-qdrd+kFfr30sd8-A@mail.gmail.com> <20201028232001.pp7erdwft7oyt2xm@ast-mbp.dhcp.thefacebook.com> <20201029025745.GA2386070@rani.riverdale.lan>
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On Wed, Oct 28, 2020 at 10:57:45PM -0400, Arvind Sankar wrote:
> On Wed, Oct 28, 2020 at 04:20:01PM -0700, Alexei Starovoitov wrote:
> > All compilers have bugs. Kernel has bugs. What can go wrong?

Heh.

> +linux-toolchains. GCC updated the documentation in 7.x to discourage
> people from using the optimize attribute.
> 
> https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff;h=893100c3fa9b3049ce84dcc0c1a839ddc7a21387

https://patchwork.ozlabs.org/project/gcc/patch/20151213081911.GA320@x4/
has all the discussion around that GCC patch.


Segher