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From: Ard Biesheuvel <ardb@kernel.org>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	bpf <bpf@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	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>
Subject: Re: [PATCH] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE
Date: Tue, 27 Oct 2020 23:23:41 +0100	[thread overview]
Message-ID: <CAMj1kXGFWr5FSiO79VYEYhB2eCpDP5vyTJmdskxrKWnUz-GP-w@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdnfkZXJdZkKO6qT53j6nH4HF=CcpUZcr7XOqdnQLSShmw@mail.gmail.com>

On Tue, 27 Oct 2020 at 23:03, Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> On Tue, Oct 27, 2020 at 2:50 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> >
> > On Tue, 27 Oct 2020 at 22:20, Nick Desaulniers <ndesaulniers@google.com> wrote:
> > >
> > > On Tue, Oct 27, 2020 at 1:57 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > > >
> > > > diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> > > > index 6e390d58a9f8..ac3fa37a84f9 100644
> > > > --- a/include/linux/compiler_types.h
> > > > +++ b/include/linux/compiler_types.h
> > > > @@ -247,10 +247,6 @@ struct ftrace_likely_data {
> > > >  #define asm_inline asm
> > > >  #endif
> > > >
> > > > -#ifndef __no_fgcse
> > > > -# define __no_fgcse
> > > > -#endif
> > > > -
> > > Finally, this is going to disable GCSE for the whole translation unit,
> > > which may be overkill.   Previously it was isolated to one function
> > > definition.  You could lower the definition of the preprocessor define
> > > into kernel/bpf/core.c to keep its use isolated as far as possible.
> > >
> >
> > Which preprocessor define?
>
> __no_fgcse
>

But we can't use that, that is the whole point of this patch.

  reply	other threads:[~2020-10-27 22:23 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-27 20:57 [PATCH] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE Ard Biesheuvel
2020-10-27 21:20 ` Nick Desaulniers
2020-10-27 21:49   ` Ard Biesheuvel
2020-10-27 22:03     ` Nick Desaulniers
2020-10-27 22:23       ` Ard Biesheuvel [this message]
2020-10-27 22:38         ` Nick Desaulniers
2020-10-27 23:04 ` Daniel Borkmann
2020-10-27 23:11   ` Nick Desaulniers
2020-10-28  8:11     ` [PATCH] tools/perf: Remove broken __no_tail_call attribute Peter Zijlstra
2020-10-28  8:14       ` Ard Biesheuvel
2020-10-28 12:24       ` Miguel Ojeda
2020-10-28  6:51   ` [PATCH] bpf: don't rely on GCC __attribute__((optimize)) to disable GCSE Ard Biesheuvel
2020-10-28  6:59     ` Ard Biesheuvel
2020-10-28  8:30 ` Geert Uytterhoeven
2020-10-29  8:38 ` David Laight

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