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Message-ID: <20170914172627.sp2yrecpawovvxxy@treble> Date: Thu, 14 Sep 2017 12:26:27 -0500 From: Josh Poimboeuf <jpoimboe@...hat.com> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Ingo Molnar <mingo@...nel.org>, the arch/x86 maintainers <x86@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Andy Lutomirski <luto@...nel.org>, Alexander Potapenko <glider@...gle.com>, Dmitriy Vyukov <dvyukov@...gle.com>, Matthias Kaehlcke <mka@...omium.org>, Arnd Bergmann <arnd@...db.de>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [RFC PATCH 3/4] x86/asm: Make alternative macro interfaces more clear and consistent On Thu, Sep 14, 2017 at 10:16:08AM -0700, Linus Torvalds wrote: > On Thu, Sep 14, 2017 at 7:48 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote: > > > > As it turns out, the real problem with this option is that it imposes a > > penalty for CONFIG_FRAME_POINTER=n: even with frame pointers disabled, > > it forces the frame pointer to be saved for each function which uses the > > inline asm "call" statements. Our current solution doesn't do that. > > But couldn't we make the whole stack pointer clobber be dependent on > CONFIG_FRAME_POINTER? > > The only reason we do it is to make sure the frame pointer is set up > before the inline asm is emitted, but with frame pointers disabled we > don't need to. We could, but then that would mean either: a) uglifying the 15 or so relevant inline asm locations with ifdefs; or b) using my ASM_CALL macro, which I think you frowned upon? -- Josh
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