linux-kernel - Re: [PATCH 2/5] jump label: base patch

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Message-ID: <4BA7DAB3.5030002@redhat.com>
Date:	Mon, 22 Mar 2010 23:01:39 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Jason Baron <jbaron@...hat.com>
CC:	linux-kernel@...r.kernel.org, mingo@...e.hu,
	mathieu.desnoyers@...ymtl.ca, hpa@...or.com, tglx@...utronix.de,
	rostedt@...dmis.org, andi@...stfloor.org, roland@...hat.com,
	rth@...hat.com, mhiramat@...hat.com, fweisbec@...il.com
Subject: Re: [PATCH 2/5] jump label: base patch

On 03/22/2010 06:07 PM, Jason Baron wrote:
> base patch to implement 'jump labeling'. Based on a new 'asm goto' inline
> assembly gcc mechanism, we can now branch to labels from an 'asm goto'
> statment. This allows us to create a 'no-op' fastpath, which can subsequently
> be patched with a jump to the slowpath code. This is useful for code which
> might be rarely used, but which we'd like to be able to call, if needed.
> Tracepoints are the current usecase that these are being implemented for.
>
>
> +
> +#define JUMP_LABEL(tag, label, cond)		\
> +	if (unlikely(cond))			\
> +		goto label;
>    

Suggest wrapping with do { } while (0) to avoid problems with the 
dangling semicolon or a trailing 'else' from an outer if ().

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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