Re: [PATCH] perf-script: check session->header.env.arch before using it

[Song Liu <songliubraving@fb.com>]

> On Oct 27, 2021, at 5:39 AM, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> 
> Em Sun, Oct 03, 2021 at 10:32:38PM -0700, Song Liu escreveu:
>> When perf.data is not written cleanly, we would like to process existing
>> data as much as possible (please see f_header.data.size == 0 condition
>> in perf_session__read_header). However, perf.data with partial data may
>> crash perf. Specifically, we see crash in perf-script for NULL
>> session->header.env.arch.
>> 
>> Fix this by checking session->header.env.arch before using it to determine
>> native_arch. Also split the if condition so it is easier to read.
>> 
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>> tools/perf/builtin-script.c | 13 +++++++++----
>> 1 file changed, 9 insertions(+), 4 deletions(-)
>> 
>> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
>> index 6211d0b84b7a6..7821f6740ac1d 100644
>> --- a/tools/perf/builtin-script.c
>> +++ b/tools/perf/builtin-script.c
>> @@ -4039,12 +4039,17 @@ int cmd_script(int argc, const char **argv)
>> 		goto out_delete;
>> 
>> 	uname(&uts);
>> -	if (data.is_pipe ||  /* assume pipe_mode indicates native_arch */
>> -	    !strcmp(uts.machine, session->header.env.arch) ||
>> -	    (!strcmp(uts.machine, "x86_64") &&
>> -	     !strcmp(session->header.env.arch, "i386")))
>> +	if (data.is_pipe)  /* assume pipe_mode indicates native_arch */
>> 		native_arch = true;
>> 
>> +	if (session->header.env.arch) {
> 
> Shouldn't the above be:
> 
> 	else if (session->header.env.arch) {
> 
> ?

Yes! That's better. 

Do you want me to send v2 with the change? 

Thanks,
Song

> 
>> +		if (!strcmp(uts.machine, session->header.env.arch))
>> +			native_arch = true;
>> +		else if (!strcmp(uts.machine, "x86_64") &&
>> +			 !strcmp(session->header.env.arch, "i386"))
>> +			native_arch = true;
>> +	}
>> +
>> 	script.session = session;
>> 	script__setup_sample_type(&script);
>> 
>> -- 
>> 2.30.2
> 
> -- 
> 
> - Arnaldo