linux-kernel - Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel

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Message-ID: <CALCETrXSn=OBBdJVTE8cUVvmOv__2qMWf9UaakrjBNkEFf9TKw@mail.gmail.com>
Date:	Fri, 17 Jul 2015 13:39:09 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>, X86 ML <x86@...nel.org>,
	live-patching@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 13/21] x86/asm/crypto: Fix frame pointer usage in aesni-intel_asm.S

On Fri, Jul 17, 2015 at 1:37 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> On Fri, Jul 17, 2015 at 12:44:42PM -0700, Andy Lutomirski wrote:
>> On Fri, Jul 17, 2015 at 12:43 PM, Ingo Molnar <mingo@...nel.org> wrote:
>> >
>> > * Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>> >
>> >>  ENTRY(aesni_set_key)
>> >> +     FRAME
>> >>  #ifndef __x86_64__
>> >>       pushl KEYP
>> >>       movl 8(%esp), KEYP              # ctx
>> >> @@ -1905,6 +1907,7 @@ ENTRY(aesni_set_key)
>> >>  #ifndef __x86_64__
>> >>       popl KEYP
>> >>  #endif
>> >> +     ENDFRAME
>> >>       ret
>> >>  ENDPROC(aesni_set_key)
>> >
>> > So cannot we make this a bit more compact and less fragile?
>> >
>> > Instead of:
>> >
>> >         ENTRY(aesni_set_key)
>> >                 FRAME
>> >         ...
>> >                 ENDFRAME
>> >                 ret
>> >         ENDPROC(aesni_set_key)
>> >
>> >
>> > How about writing this as:
>> >
>> >         FUNCTION_ENTRY(aesni_set_key)
>> >         ...
>> >         FUNCTION_RETURN(aesni_set_key)
>> >
>> > which does the same thing in a short, symmetric construct?
>> >
>> > One potential problem with this approach would be that what 'looks' like an entry
>> > declaration, but it will now generate real code.
>> >
>> > OTOH if people find this intuitive enough then it's a lot harder to mess it up,
>> > and I think 'RETURN' makes it clear enough that there's a real instruction
>> > generated there.
>> >
>>
>> How about FUNCTION_PROLOGUE and FUNCTION_EPILOGUE?
>
> Perhaps the macro name should describe what the epilogue does, since
> frame pointers aren't required for _all_ functions, only those which
> don't have call instructions.
>
> What do you think about ENTRY_FRAME and ENDPROC_FRAME_RETURN?  The
> ending macro is kind of long, but at least it a) matches the existing
> ENTRY/ENDPROC convention for asm functions; b) gives a clue that frame
> pointers are involved; and c) lets you know that the return is there.
>

This really is about frame pointers, right?  How about
ENTRY_FRAMEPTR_xyz where xyz can be prologue, epilogue, return,
whatever?

> --
> Josh



-- 
Andy Lutomirski
AMA Capital Management, LLC
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