linux-kernel - Re: [PATCH] perf kvm: fix segfault with default guest arguments

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Message-ID: <4FEC6F7E.2030905@gmail.com>
Date:	Thu, 28 Jun 2012 08:51:42 -0600
From:	David Ahern <dsahern@...il.com>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
CC:	linux-kernel@...r.kernel.org, psuriset@...ux.vnet.ibm.com,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] perf kvm: fix segfault with default guest arguments

On 6/28/12 8:44 AM, Arnaldo Carvalho de Melo wrote:
> Em Sun, Jun 24, 2012 at 10:41:26PM -0600, David Ahern escreveu:
>> File generated with:
>> $ perf kvm --host --guest --guestkallsyms=/tmp/guest-kallsyms
>>      --guestmodules=/tmp/guest-modules record -a
>>
>> The report command:
>> $ perf kvm --host --guest --guestkallsyms=/tmp/guest-kallsyms
>>      --guestmodules=/tmp/guest-modules report
>>
>> dies with a SEGFAULT:
>> Program received signal SIGSEGV, Segmentation fault.
>> 0x000000000046dd7b in machine__mmap_name (self=0x0, bf=0x7fffffffbd20 "q\021", size=4096) at util/map.c:715
>> 715			snprintf(bf, size, "[%s.%d]", "guest.kernel.kallsyms", self->pid);
>>
>> (gdb) bt
>> 0  0x000000000046dd7b in machine__mmap_name (self=0x0, bf=0x7fffffffbd20 "q\021", size=4096) at util/map.c:715
>> 1  0x0000000000444161 in perf_event__process_kernel_mmap (tool=0x7fffffffdd80, event=0x7ffff7fb4120, machine=0x0) at util/event.c:562
>
> I think that this should be handled at perf_event__process_kernel_mmap,
> i.e. tools can conceivably handle this situation in their specific
> handlers.
>
>>   @@ -976,6 +976,8 @@ static int perf_session_deliver_event(struct perf_session *session,
>>   		}
>>   		return tool->sample(tool, event, sample, evsel, machine);
>>   	case PERF_RECORD_MMAP:
>> +		if (machine == NULL)
>> +			return 0;
>>   		return tool->mmap(tool, event, sample, machine);
>>
> - Arnaldo
>

Ok. Doing it in perf_session_deliver_event makes it consistent with the 
SAMPLE case.

David
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