linux-kernel - Re: [PATCH 03/10] jump label v11: base patch

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Message-ID: <4C990070.7080807@zytor.com>
Date:	Tue, 21 Sep 2010 11:58:56 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Jason Baron <jbaron@...hat.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, mathieu.desnoyers@...ymtl.ca, tglx@...utronix.de,
	rostedt@...dmis.org, andi@...stfloor.org, roland@...hat.com,
	rth@...hat.com, mhiramat@...hat.com, fweisbec@...il.com,
	avi@...hat.com, davem@...emloft.net, vgoyal@...hat.com,
	sam@...nborg.org, tony@...eyournoodle.com
Subject: Re: [PATCH 03/10] jump label v11: base patch

On 09/21/2010 11:55 AM, Konrad Rzeszutek Wilk wrote:
>>> +early_initcall(init_jump_label);
>>
>> Is there any danger of not patching the instructions with NOPs before
>> early_initcall is called? I guess for your uses (tracing) there won't.
>> And even if there are not patched it will just call the function.
> 
> Ah, nevermind - if you don't patch the addresses which are in
> _jump_label section, the untouched code will just do far jump (jmpq)
> to right after the macro, which is ok.

Technical point of order: jmpq is *NOT* a far jump.  A far jump (called
ljmp in gas) is a completely different x86 instruction with *very*
different semantics.

	-hpa

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