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

From: Mathieu Desnoyers
Date: Thu Sep 21 2006 - 22:06:51 EST


* Jeremy Fitzhardinge (jeremy@xxxxxxxx) 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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