[PATCH 4/5] perf tools: [uclibc] don't rely on glibc malloc working for sz 0

[Vineet Gupta]

When running perf on ARC (uClibc based userspace), ran into this issue
------------->8----------------
	[ARCLinux]$ ./perf record ls
	bin             etc             perf            sys
	debug           init            perf.data       tmp
	[ perf record: Woken up 1 times to write data ]
	[ perf record: Captured and wrote 0.001 MB perf.data (~24 samples) ]

	[ARCLinux]$ ./perf report
	incompatible file format (rerun with -v to learn more)
------------->8----------------

The problem happens in the following call stack when zalloc is called
with size zero

glibc default / uClibc with MALLOC_GLIBC_COMPAT are OK, but not if that
config option is not enabled.

  cmd_report
     perf_session__new
	perf_session__open
	    perf_session__read_header
		read_attr(fd, header, &f_attr)
		nr_ids = f_attr.ids.size / sizeof(u64); <-- 0
		perf_evsel__alloc_id(vsel, 1, nr_ids)
			zalloc(ncpus * nthreads * sizeof(u64)) <-- 0

header.c: read_attr()

(gdb) p *f_attr
$17 = {
  attr = {
    type = 0,
    size = 96,
    config = 0,
    {
      sample_period = 4000,
      sample_freq = 4000
    },
...
  ids = {
    offset = 104,
    size = 0      <------
  }
}

Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
---
 tools/perf/util/header.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index b20e40c74468..43671068ce75 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -2532,7 +2532,7 @@ int perf_session__read_header(struct perf_session *session)
 		 */
 		perf_evlist__add(session->evlist, evsel);
 
-		nr_ids = f_attr.ids.size / sizeof(u64);
+		nr_ids = f_attr.ids.size / sizeof(u64) ? : 1;
 		/*
 		 * We don't have the cpu and thread maps on the header, so
 		 * for allocating the perf_sample_id table we fake 1 cpu and
-- 
1.9.1

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