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Date: Thu, 28 Jun 2012 08:52:56 -0600
From: David Ahern <dsahern@gmail.com>
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To: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
CC: linux-kernel@vger.kernel.org, psuriset@linux.vnet.ibm.com,
        Ingo Molnar <mingo@kernel.org>, Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@gmail.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] perf kvm: fix segfault with default guest arguments
References: <1340599286-89757-1-git-send-email-dsahern@gmail.com> <20120628144418.GG4038@infradead.org>
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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