Re: [PATCH] perf: do not flush maps on COMM for perf report

[Ingo Molnar <mingo@kernel.org>]

* Luigi Semenzato <semenzato@chromium.org> wrote:

> This fixes a long-standing bug caused by the lack of separate
> COMM and EXEC record types, which makes "perf report" lose
> track of symbols when a process renames itself.
> 
> With this fix (suggested by Stephane Eranian), a COMM (rename)
> no longer flushes the maps, which is the correct behavior.
> An EXEC also no longer flushes the maps, but this doesn't
> matter because as new mappings are created (for the executable
> and the libraries) the old mappings are automatically removed.
> This is not by accident: the functionality is necessary because
> DLLs can be explicitly loaded at any time with dlopen(),
> possibly on top of existing text, so "perf report" handles
> correctly the clobbering of new mappings on top of old ones.
> 
> An alternative patch (which I proposed earlier) would be to
> introduce a separate PERF_RECORD_EXEC type, but it is a much
> larger change (about 300 lines) and is not necessary.

It would be nice to add that too - we already have FORK/EXIT, 
this seems like a natural extension.

Thanks,

	Ingo