[llvm-dev] Profiling data structure

[Teresa Johnson via llvm-dev]

+David Li and Vedant Kumar who are active in this area

On Wed, Oct 25, 2017 at 2:06 AM, Roger Pau Monné via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Adding who I think are the maintainers of the profile related llvm
> bits, sorry should have done that earlier.
>
> On Wed, Oct 25, 2017 at 08:26:18AM +0100, Roger Pau Monné via llvm-dev
> wrote:
> > Hello,
> >
> > I've been working on implementing some basic functionality in order to
> > use the llvm profiling functionality inside of a kernel (the Xen
> > hypervisor). The only functionality I'm interested in is being able to
> > reset the counters, get the size of the data, and dump the data into a
> > memory buffer.
> >
> > I have to admit I haven't been able to find a lot of documentation
> > about how this data is stored inside of the different sections, but
> > with the code in compiler_rt/libs/profile I've been able to craft
> > something that seems to do something sensible.
> >
> > I have however a couple of questions:
> >
> >  - The "Values" field in __llvm_profile_data always seems to be NULL.
> >    Is this expected? What/why could cause this?
> >
> >  - The fields in the NumValueSites array inside of __llvm_profile_data
> >    also seem to always be 0.
> >
> >  - Since what I'm coding is a decoupled replacement for the profiling
> >    runtime inside of compiler_rt, is there anyway that at compile or
> >    run time I can fetch the version of the profiling data?
> >    I'm mostly worried that at some point llvm will bump the version
> >    and change the layout, and then I will have to update my runtime
> >    accordingly, but without llvm reporting the version used by the
> >    compiler it's going to be very hard to keep backwards
> >    compatibility or to detect version bumps.
> >
> > Thanks, Roger.
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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-- 
Teresa Johnson |  Software Engineer |  tejohnson at google.com |  408-460-2413
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