linux-kernel - Re: [PATCH] Linux Kernel Markers 0.7 for 2.6.17 (with type checking!)

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Date:	Thu, 21 Sep 2006 20:59:28 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
CC:	Martin Bligh <mbligh@...gle.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	prasanna@...ibm.com, Andrew Morton <akpm@...l.org>,
	Ingo Molnar <mingo@...e.hu>, Paul Mundt <lethal@...ux-sh.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>,
	Richard J Moore <richardj_moore@...ibm.com>,
	Michel Dagenais <michel.dagenais@...ymtl.ca>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org,
	systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] Linux Kernel Markers 0.7 for 2.6.17 (with type checking!)

Mathieu Desnoyers wrote:
> * Jeremy Fitzhardinge (jeremy@...p.org) wrote:
>   
>> Mathieu Desnoyers wrote:
>>     
>>> #define MARK_SYM(name) \
>>>        do { \
>>>                __label__ here; \
>>>                volatile static void *__mark_kprobe_##name \
>>>                        asm (MARK_CALL_PREFIX#name) \
>>>                        __attribute__((unused)) = &&here; \
>>> here: \
>>>                do { } while(0); \
>>>        } while(0)
>>>
>>> Which fixes the problem. Some tests showed me that the compiler does not 
>>> unroll
>>> an otherwise unrolled loop when this specific macro is called. (test done 
>>> with
>>> -funroll-all-loops).
>>>       
>> Eh?  I thought you wanted to avoid changing the generated code?  
>> Inhibiting loop unrolling could be a pretty large change...
>>
>>     
>
> Yes, if possible. But letting gcc duplicate those symbols brings many questions,
> such as : how can we name each of them differently ? Is there any way to
> automatically increment an "identifier" counter in assembly ?

Use a section instead:

struct marker {
	const char *name;
	const void *location;
};

#define MARKER_SYM(name)
	do {
		__label__ here;
	here:	asm volatile(".section \".markers\"; .long %0, %1; .previous" : : "m" (#name), "m" (*&&here));\
	} while(0);

Not a linker symbol, but it does let you find all the places containing 
a particular mark.

    J
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