perf tools: do not flush maps on COMM for perf report

perf tools: do not flush maps on COMM for perf report

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.

Signed-off-by: Luigi Semenzato <[email protected]>
Tested-by: Stephane Eranian <[email protected]>
Acked-by: Stephane Eranian <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Lucas De Marchi <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Olof Johansson <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Robert Richter <[email protected]>
Cc: Sonny Rao <[email protected]>
Cc: Stephane Eranian <[email protected]>
Cc: Stephen Wilson <[email protected]>
Cc: Tejun Heo <[email protected]>
Cc: Vasiliy Kulikov <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>