Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more clear and consistent

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	Alexander Potapenko <glider@google.com>,
	Dmitriy Vyukov <dvyukov@google.com>,
	Matthias Kaehlcke <mka@chromium.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Peter Zijlstra <peterz@infradead.org>
Subject: Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more clear and consistent
Date: Thu, 14 Sep 2017 11:28:30 -0700	[thread overview]
Message-ID: <CA+55aFz223ca89MW+GR_3_cRtfuxkWUkF1H1S2JvLYWtdZkFYA@mail.gmail.com> (raw)
In-Reply-To: <20170914173348.jeddpkfc52dj2jvq@treble>

On Thu, Sep 14, 2017 at 10:33 AM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>>
>>  a) uglifying the 15 or so relevant inline asm locations with ifdefs; or
>
> Actually I guess we could put the "sp" in a macro...  I'll try it.

Exactly. Do something like

   #ifdef CONFIG_FRAME_POINTER
   # define EXTRA_ASM_CLOBBERS "rsp"
   #else
   # define EXTRA_ASM_CLOBBERS
   #endif

and then replace the nasty

        register void *__sp asm(_ASM_SP);
        ..
        "+r" (__sp)

games with just that EXTRA_ASM_CLOBBERS thing at the end of the clobbers.

Yes, you'd probably have to document that the alternative_call_2()
thing doesn't take a "input" argument, but a input_and_clobbers, but
all users do that anyway.

I dunno.

               Linus