linux-kernel - Re: [PATCH] x86: Introduce REX prefix helper for kprobes

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Message-Id: <1199036395.6323.41.camel@brick>
Date:	Sun, 30 Dec 2007 09:39:55 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Masami Hiramatsu <mhiramat@...hat.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86: Introduce REX prefix helper for kprobes

On Sat, 2007-12-29 at 23:04 -0800, H. Peter Anvin wrote:
> Masami Hiramatsu wrote:
> > Hi Harvey,
> > 
> > Harvey Harrison wrote:
> >> Fold some small ifdefs into a helper function.
> >>
> >> Signed-off-by: Harvey Harrison <harvey.harrison@...il.com>
> >> ---
> >> Masami, Ingo, I had this left in some unsent kprobes unification
> >> work.  Depends on your tastes, but does reduce ifdefs and is a bit
> >> better about self-documenting the REX prefix on X86_64.
> > 
> > Basically, I think it is good idea.
> > Could you use a macro same as the stack_addr() macro, like as below?
> > 
> > #defile is_REX_prefix(insn) ((insn & 0xf0) == 0x40))
> > 
> > This is just a bit checker, so I think a macro is better to do that.
> > 
> 
> Why is a macro better than an inline, and why the odd mIXed case?
> 

I was emulating existing practice I saw in kprobes, see is_IF_modifier.

Harvey

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