Commit 331c7cb3 authored by Ravi Bangoria's avatar Ravi Bangoria Committed by Arnaldo Carvalho de Melo

perf symbols: Fix memory corruption because of zero length symbols

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.


  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

  static int __symbol__inc_addr_samples(...)
        offset = addr - sym->start;
        h = annotation__histogram(notes, evidx);
        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.

Fixes: edee44be ("perf annotate: Don't throw error for zero length symbols")
Signed-off-by: default avatarRavi Bangoria <>
Acked-by: default avatarJiri Olsa <>
Acked-by: default avatarNamhyung Kim <>
Cc: Alexander Shishkin <>
Cc: Jin Yao <>
Cc: Kim Phillips <>
Cc: Naveen N. Rao <>
Cc: Peter Zijlstra <>
Cc: Taeung Song <>
Link: default avatarArnaldo Carvalho de Melo <>
parent 2eece390
......@@ -606,9 +606,19 @@ static struct arch *arch__find(const char *name)
int symbol__alloc_hist(struct symbol *sym)
struct annotation *notes = symbol__annotation(sym);
const size_t size = symbol__size(sym);
size_t size = symbol__size(sym);
size_t sizeof_sym_hist;
* Add buffer of one element for zero length symbol.
* When sample is taken from first instruction of
* zero length symbol, perf still resolves it and
* shows symbol name in perf report and allows to
* annotate it.
if (size == 0)
size = 1;
/* Check for overflow when calculating sizeof_sym_hist */
if (size > (SIZE_MAX - sizeof(struct sym_hist)) / sizeof(struct sym_hist_entry))
return -1;
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