Jin Yao reported memory corrupton in perf report with
branch info used for stack trace:

  > Following command lines will cause perf crash.

  > perf record -j call -g -a <application>
  > perf report --branch-history
  >
  > *** Error in `perf': double free or corruption (!prev): 0x00000000104aa040 ***
  > ======= Backtrace: =========
  > /lib/x86_64-linux-gnu/libc.so.6(+0x77725)[0x7f6b37254725]
  > /lib/x86_64-linux-gnu/libc.so.6(+0x7ff4a)[0x7f6b3725cf4a]
  > /lib/x86_64-linux-gnu/libc.so.6(cfree+0x4c)[0x7f6b37260abc]
  > perf[0x51b914]
  > perf(hist_entry_iter__add+0x1e5)[0x51f305]
  > perf[0x43cf01]
  > perf[0x4fa3bf]
  > perf[0x4fa923]
  > perf[0x4fd396]
  > perf[0x4f9614]
  > perf(perf_session__process_events+0x89e)[0x4fc38e]
  > perf(cmd_report+0x15d2)[0x43f202]
  > perf[0x4a059f]
  > perf(main+0x631)[0x427b71]
  > /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7f6b371fd830]
  > perf(_start+0x29)[0x427d89]

For the cumulative output, we allocate the he_cache array based on the
--max-stack option value and populate it with data from 'callchain_cursor'.

The --max-stack option value does not ensure now the limit for number of
callchain_cursor nodes, so the cumulative iter code will allocate smaller array
than it's actually needed and cause above corruption.

I think the --max-stack limit does not apply here anyway, because we add
callchain data as normal hist entries, while the --max-stack control the limit
of single entry callchain depth.

Using the callchain_cursor.nr as he_cache array count to fix this. Also
removing struct hist_entry_iter::max_stack, because there's no longer any use
for it.

We need more fixes to ensure that the branch stack code follows properly the
logic of --max-stack, which is not the case at the moment.
Original-patch-by: Jin Yao <yao.jin@linux.intel.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Reported-by: Jin Yao <yao.jin@linux.intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180216123619.GA9945@kravaSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>