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