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Ravi Bangoria authored
Perf top is often crashing at very random locations on powerpc. After investigating, I found the crash only happens when sample is of zero length symbol. Powerpc kernel has many such symbols which does not contain length details in vmlinux binary and thus start and end addresses of such symbols are same. Structure struct sym_hist { u64 nr_samples; u64 period; struct sym_hist_entry addr[0]; }; has last member 'addr[]' of size zero. 'addr[]' is an array of addresses that belongs to one symbol (function). If function consist of 100 instructions, 'addr' points to an array of 100 'struct sym_hist_entry' elements. For zero length symbol, it points to the *empty* array, i.e. no members in the array and thus offset 0 is also invalid for such array. static int __symbol__inc_addr_samples(...) { ... offset = addr - sym->start; h = annotation__histogram(notes, evidx); h->nr_samples++; h->addr[offset].nr_samples++; h->period += sample->period; h->addr[offset].period += sample->period; ... } Here, when 'addr' is same as 'sym->start', 'offset' becomes 0, which is valid for normal symbols but *invalid* for zero length symbols and thus updating h->addr[offset] causes memory corruption. Fix this by adding one dummy element for zero length symbols. Link: https://lkml.org/lkml/2016/10/10/148 Fixes: edee44be ("perf annotate: Don't throw error for zero length symbols") Signed-off-by:
Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com> Acked-by:
Jiri Olsa <jolsa@kernel.org> Acked-by:
Namhyung Kim <namhyung@kernel.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Jin Yao <yao.jin@linux.intel.com> Cc: Kim Phillips <kim.phillips@arm.com> Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Taeung Song <treeze.taeung@gmail.com> Link: http://lkml.kernel.org/r/1508854806-10542-1-git-send-email-ravi.bangoria@linux.vnet.ibm.comSigned-off-by:
Arnaldo Carvalho de Melo <acme@redhat.com>
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