netdev - Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute_

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Message-ID: <20201029203113.GJ2672@gate.crashing.org>
Date:   Thu, 29 Oct 2020 15:31:13 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
        <netdev@...r.kernel.org>,
        "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" 
        <bpf@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Kees Cook <keescook@...omium.org>,
        linux-toolchains@...r.kernel.org
Subject: Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE

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