perf per-symbol histogram causes memory corruption

[David Miller]

When builtin-annotate.c processes sample events via
process_sample_event() it uses 'sample_filter'

sample_filter() sizes the histogram object for a symbol based upon the
size, calculated as "sym->end - sym->start", to determine the number
of IP sample slots to allocate.

The problem is, the sym->end value is not stable at this point.

For example, dso__load_sym() first loads all of the symbols, then it
makes another pass over the symbols by calling symbols__fixup_end()
which will adjust the sym->end values of various symbols.

At this point, the histogram IP sample array allocated by
sample_filter() can become too small, and hits recorded can thus
access past the end of the array corrupting memory.

I get this very reliably on sparc64, and it took me a few days to root
cause this. :-)

I don't see an immediate way to fix this, any ideas?

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