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Re: [PATCH] Linux Kernel Markers 0.7 for 2.6.17 (with type checking!)
- From: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- To: Jeremy Fitzhardinge <jeremy at goop dot org>
- Cc: Martin Bligh <mbligh at google dot com>, "Frank Ch. Eigler" <fche at redhat dot com>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, Ingo Molnar <mingo at elte dot hu>, Paul Mundt <lethal at linux-sh dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, Jes Sorensen <jes at sgi dot com>, Tom Zanussi <zanussi at us dot ibm dot com>, Richard J Moore <richardj_moore at uk dot ibm dot com>, Michel Dagenais <michel dot dagenais at polymtl dot ca>, Christoph Hellwig <hch at infradead dot org>, Greg Kroah-Hartman <gregkh at suse dot de>, Thomas Gleixner <tglx at linutronix dot de>, William Cohen <wcohen at redhat dot com>, ltt-dev at shafik dot org, systemtap at sources dot redhat dot com, Alan Cox <alan at lxorguk dot ukuu dot org dot uk>
- Date: Fri, 22 Sep 2006 11:27:37 -0400
- Subject: Re: [PATCH] Linux Kernel Markers 0.7 for 2.6.17 (with type checking!)
- References: <20060921232024.GA16155@Krystal> <451331A1.3020601@goop.org> <20060922020119.GA28712@Krystal> <45134539.7070305@goop.org> <20060922021400.GA6330@Krystal> <45135FA0.1030403@goop.org>
* Jeremy Fitzhardinge (jeremy@goop.org) wrote:
> Mathieu Desnoyers wrote:
> >* Jeremy Fitzhardinge (jeremy@goop.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.
>
Very clever idea, as it lessens the impact on the compiler optimisations. Any
ideas about how we could fit in a list of "read" memory constraints based on a
vargs list in the macro ?
Mathieu
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