Re: perf per-symbol histogram causes memory corruption

[Ingo Molnar <mingo@elte.hu>]

(Added Arnaldo to the Cc: - he's maintaining the symbol lookup bits of perf.)

* David Miller <davem@davemloft.net> wrote:

> 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?