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

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Message-ID: <20060922020119.GA28712@Krystal>
Date:	Thu, 21 Sep 2006 22:01:19 -0400
From:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
To:	Jeremy Fitzhardinge <jeremy@...p.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!)

* Jeremy Fitzhardinge (jeremy@...p.org) wrote:
> Mathieu Desnoyers wrote:
> >+#ifdef CONFIG_MARK_SYMBOL
> >+#define MARK_SYM(name) \
> >+	do { \
> >+		__label__ here; \
> >+		here: asm volatile \
> >+			(MARK_KPROBE_PREFIX#name " = %0" : : "m" (*&&here)); 
> >\
> >+	} while(0)
> >+#else 
> >+#define MARK_SYM(name)
> >+#endif
> 
> BTW, this won't work if you put the MARK_SYM in a loop which gcc 
> unrolls; you'll only get the mark in the last unrolled iteration 
> (because the symbol assignments will override each other).
> 
> Do make this work properly, you really need to put the mark entries into 
> a separate section, so that if gcc duplicates the code, you get 
> duplicated markers too.
> 

Good point, I will change it to :

#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).

Regards,

Mathieu


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