Re: [PATCH v2 1/2] bpf: don't rely on GCC attribute((optimize)) to disable GCSE

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Subject: Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
From: Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx>
Date: Thu, 29 Oct 2020 15:31:13 -0500
Cc: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>, Ard Biesheuvel <ardb@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" <netdev@xxxxxxxxxxxxxxx>, "open list:BPF JIT for MIPS (32-BIT AND 64-BIT)" <bpf@xxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, Nick Desaulniers <ndesaulniers@xxxxxxxxxx>, Randy Dunlap <rdunlap@xxxxxxxxxxxxx>, Josh Poimboeuf <jpoimboe@xxxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Alexei Starovoitov <ast@xxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Peter Zijlstra <peterz@xxxxxxxxxxxxx>, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>, Kees Cook <keescook@xxxxxxxxxxxx>, linux-toolchains@xxxxxxxxxxxxxxx
In-reply-to: <20201029025745.GA2386070@rani.riverdale.lan>
User-agent: Mutt/1.4.2.3i

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

Follow-Ups:
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Ard Biesheuvel

References:
- [PATCH v2 0/2] get rid of GCC __attribute__((optimize)) for BPF
  - From: Ard Biesheuvel
- [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Ard Biesheuvel
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Alexei Starovoitov
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Ard Biesheuvel
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Alexei Starovoitov
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Ard Biesheuvel
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Alexei Starovoitov
- Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
  - From: Arvind Sankar

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Re: [PATCH v2 1/2] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE

Re: [PATCH v2 1/2] bpf: don't rely on GCC attribute((optimize)) to disable GCSE