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

Namhyung Kim
2015-01-08T07:53:32Z

Hi Vineet,

On Tue, Jan 06, 2015 at 07:22:14PM +0530, Vineet Gupta wrote:
> 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 <------
> }
> }

Hmm.. okay. I think we don't need to allocate the id arrays when size
is 0. So perf_event__process_attr() will have the same problem IMHO.
How about this?

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 1e90c8557ede..1d826d63bc20 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -797,6 +797,9 @@ int perf_evsel__enable(struct perf_evsel *evsel, int ncpus, int nthreads)

int perf_evsel__alloc_id(struct perf_evsel *evsel, int ncpus, int nthreads)
{
+ if (ncpus == 0 || nthreads == 0)
+ return 0;
+
if (evsel->system_wide)
nthreads = 1;