linux-kernel - Re: [PATCH ftrace.git] Immedate Values Optimized Jump Fix

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Message-ID: <48812902.5070003@zytor.com>
Date:	Fri, 18 Jul 2008 16:36:34 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
CC:	Ingo Molnar <mingo@...e.hu>, Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH ftrace.git] Immedate Values Optimized Jump Fix

Mathieu Desnoyers wrote:
> 
> Hrm, I thought that by following the execution flow to both branches and
> by looking at the code pattern found (load immediate, test, branch) and
> by placing a constraint on the eax register to detect the liveliness
> region of that variable we would be guaranteed that the compiler could
> not re-use this variable outside of the pattern scope.
> 

Nope, and you *cannot* allow such registers to be live *anywhere* the C 
compiler is generating code, even between two asm() statements with 
nothing in between.

	-hpa
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