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

[David Ahern]

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

So this is the root cause of the SEGFAULT:

743eb868657bdb1b26c7b24077ca21c67c82c777 is the first bad commit
commit 743eb868657bdb1b26c7b24077ca21c67c82c777
Author: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Date:   Mon Nov 28 07:56:39 2011 -0200

    perf tools: Resolve machine earlier and pass it to perf_event_ops

    Reducing the exposure of perf_session further, so that we can use the
    classes in cases where no perf.data file is created.

    Cc: David Ahern <dsahern@xxxxxxxxx>
    Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
    Cc: Mike Galbraith <efault@xxxxxx>
    Cc: Paul Mackerras <paulus@xxxxxxxxx>
    Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
    Cc: Stephane Eranian <eranian@xxxxxxxxxx>
    Link: 
http://lkml.kernel.org/n/tip-stua66dcscsezzrcdugvbmvd@xxxxxxxxxxxxxx
    Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

:040000 040000 414f7e982a230f633440b3da2900da4d2d9c30ef
3231e148910bd596c61814e18bba77ecf7ad5dfb M  tools


specifically, this part:

-   machine = perf_session__findnew_machine(session, event->mmap.pid);
-   if (!machine) {
-       pr_err("Can't find id %d's machine\n", event->mmap.pid);
-       goto out_problem;
-   }
-

Suggestions on how to fix that part?

More to the perf-kvm story; details in future emails.

David
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