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Re: Build IDs for finding packages

On Wed, 2013-01-30 at 14:50 -0300, Arnaldo Carvalho de Melo wrote:
> Right now we have to, at the end of the 'perf record' session,
> traverse the generated files looking for DSOs that had
> samples, and then generating a header with the build-ids.
> This has issues with long running sessions where updates can take
> place and also there is this overhead at the end of the session, so
> one item in the 'perf' TODO list[1] is to add the build-id to the
> PERF_RECORD_MMAP event to fix this.

This would also be useful for systemtap which currently does this at
runtime itself when it is running in kernel mode. At translation time it
records the build-ids for the code it is expecting to place probes in
and for which it has symbol/unwind tables available. Then at runtime it
checks them against the vmas mapped in. See _stp_build_id_check in
runtime/sym.c. Having some mechanism in the kernel to easily catch vmas
that are mapped in associated with a particular build-id and/or not
having to grovel through memory by hand to get at the build-id
associated with a vma would be nice. Do you already have some
design/patch for this?



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