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

[Vineet Gupta]

On Thursday 08 January 2015 01:23 PM, Namhyung Kim wrote:
> 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;

Fine by me as I'm not too familiar with perf tools internals.
So I need to spin a v2 for this or would you rather create a patch with me as
Reported-by:

-Vineet
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