linux-kernel - Re: [PATCH 2/6] x86: bug: prevent gcc distortions

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Message-ID: <6DB0E0C2-CCD2-4FCE-BD8B-5E340E308FF7@vmware.com>
Date:   Fri, 18 May 2018 17:24:27 +0000
From:   Nadav Amit <namit@...are.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Peter Anvin <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 2/6] x86: bug: prevent gcc distortions

Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Fri, May 18, 2018 at 12:59 AM Peter Zijlstra <peterz@...radead.org>
> wrote:
> 
>> This is an awesome hack, but is there really nothing we can do to make
>> it more readable? Esp, that global asm doing the macro definition is a
>> pain to read.
> 
> I actually find that macro to be *more* legible than what we do now,
> although I'm not enamored with the pseudo-operation name ("__BUG_FLAGS").
> 
> That said, the C header code itself I don't love.
> 
> I wonder if we should just introduce a new assembler header file, and get
> it included when processing compiler-generated asm. We already do that for
> our _real_ *.S files, with a number of our header files having constants
> and code for the asm case too, not just C.
> 
> But we could have an <asm/asm-macro.h> header file that has these kinds of
> macros (or "pseudo-instructions") for assembly language cases, and then we
> could just rely on them in inline asm.

Will it be ok just to use a global inline asm to set an “.include” directive
that gas would later process? (I can probably wrap it in a C macro so it
won’t be too disgusting)