Messages in this thread | | | Date | Mon, 25 Sep 2006 19:28:28 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [PATCH] Linux Kernel Markers 0.11 for 2.6.17 |
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Hi,
* Frank Ch. Eigler (fche@redhat.com) wrote: > Hi - > > > [...] > > - It _does not_ change the compiler optimisations. > > Like any similar mechanism, it does force the compiler to change its > code generation, so one can't claim this too strongly. > Yes, memory dependencies are changed, you are right. I was principally talking about the inline and unrolled loops optimisations.
> > [...] Comments are welcome, > > I'm still uneasy about the use of varargs. The current code now uses > the formatting string as metadata to be matched (strcmp) between > producer and consumer. A general tool that would use them would have > to start parsing general printf directives.
If you want to generate probes automatically, yes.
> I believe they are not > quite general enough either e.g. to describe a raw binary blob. > If you want to dump a raw binary blob, what about : MARK(mysubsys_myevent, "char %p %u", blobptr, blobsize); where %p is a pointer to an array of char and %u the length ?
My idea is to use the string to identify what is referred by a pointer, so it can be casted into this type with some kind of coherency between the marker and the probe.
> I realize they serve a useful purpose in abbreviating what otherwise > one might have to do (like that multiplicity of STAP_MARK_* type/arity > permutations). But maybe there is a better way. >
I think that duplicating the number of marker macros could easily make them unflexible and ugly. This is why I am trying to come with this generic macro.
> Also, while regparm(0) may provide some comfort on x86, is there good > reason to believe that the same trick works (and will continue to > work) on non-x86 platforms to invoke a non-varargs callee with a > varargs caller? >
Good point, I will setup a va_args in the probe. When correctly used, however, there is no need to use the format string : we can directly get the variables from the var arg list if we know in advance what the string will be.
Mathieu
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