On Wed, Aug 22, 2012 at 12:28 AM, Ingo Molnar <mi...@kernel.org> wrote: > > * Luigi Semenzato <semenz...@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.
Yes. Adding PERF_RECORD_EXEC is/would be the right long-term solution. But there are two issues. 1. One nice aspect of perf is that perf.data files and "perf report" are compatible across a large number of versions. Adding PERF_RECORD_EXEC breaks compatibility in a somewhat unpleasant manner. New perf.data files won't work with old versions of perf and *might* fail poorly (segv) although this situation is difficult to analyze. 2. Adding a new record type is messy. It replicates a lot of boilerplate code, much of it in the kernel, and affects many parts of the system. It adds to size, complexity, and likelihood of new bugs. I would prioritize the "would be nice" category as follows. 1. Improve the handling of unknown record types for future better backward compatibility. (Small change.) 2. Refactor/cleanup code to improve readability and robustness. (Big change, but can be broken into many smaller pieces.) 3. Add PERF_RECORD_EXEC. If there is consensus, I might be able to give a shot to 1 and 2 (courtesy of Google). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/