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

[Nick Desaulniers]

On Tue, Oct 27, 2020 at 2:50 PM Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Tue, 27 Oct 2020 at 22:20, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote:
> >
> > On Tue, Oct 27, 2020 at 1:57 PM Ard Biesheuvel <ardb@xxxxxxxxxx> 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

>
> > I'm fine with either approach, but we should avoid new warnings for
> > clang.  Thanks for the patch!

-- 
Thanks,
~Nick Desaulniers