linux-kernel - Re: [PATCH] x86/xsave: Robustify and merge macros

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Message-ID: <20150403174824.GL3418@pd.tnic>
Date:	Fri, 3 Apr 2015 19:48:24 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc:	X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH] x86/xsave: Robustify and merge macros

On Fri, Apr 03, 2015 at 07:33:06PM +0200, Quentin Casasnovas wrote:
> > Basically, the idea was:
> > 
> > .skip len(repl1) - len(orig), 0x90
> > .skip len(repl2) - len(repl1), 0x90
> > 
> > BUT!, for some reason I changed it to what's there now and I can't
> > remember why anymore.
> 
> I think it would not work in the case where repl1 is smaller or equal than
> orig_insn (i.e. no padding in the first .skip) but orig_insn is strictly
> smaller than repl2 (since we're never comparing repl2 with insn in this
> new-old code).

orig_insn=4
repl1=3
repl2=5

.skip 0, 0x90
.skip 2, 0x90

I think that still works, only the padding is larger than it needs to
be. And it is so many bytes larger as len(abs(repl1 - orig_insn)) is.

In the example above, we'll get two bytes padding while only 1 suffices.

> Anything wrong with the two different approaches I've suggested in my
> original mail?

Right now, I want to have a minimal fix for obvious reasons. We can
always improve stuff later when there's more time.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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