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

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Message-ID: <20150717211019.GE12761@treble.redhat.com>
Date:	Fri, 17 Jul 2015 16:10:19 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
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 02:01:33PM -0700, Andy Lutomirski wrote:
> On Fri, Jul 17, 2015 at 1:59 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> > On Fri, Jul 17, 2015 at 01:46:39PM -0700, Andy Lutomirski wrote:
> >> On Fri, Jul 17, 2015 at 1:44 PM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
> >> > On Fri, Jul 17, 2015 at 01:39:09PM -0700, Andy Lutomirski wrote:
> >> >> 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?
> >> >
> >> > Wouldn't the "ENTRY" in ENTRY_FRAMEPTR_RETURN be confusing at the end of
> >> > a function?
> >>
> >> I meant ENTRY_FRAMEPTR_xyz and the beginning and ENDPROC_FRAMEPTR_xyz
> >> (ENTRY is debatable, but that's what we currently have).  ENDPROC
> >> could easily be replaced with anything else.
> >
> > So do you mean ENTRY_FRAMEPTR_PROLOGUE and ENDPROC_FRAMEPTR_EPILOGUE?
> > Or something else?
> >
> 
> I like it.  I think this bikeshed might be well painted now!

Actually I'm not done painting.  Personally it seems a little too
verbose.  I still like ENTRY_FRAME and ENDPROC_FRAME_RETURN :p

-- 
Josh
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