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Date: Thu, 30 Jan 2014 15:15:30 -0300
From: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org,
        David Ahern <dsahern@gmail.com>,
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        Mike Galbraith <efault@gmx.de>, Namhyung Kim <namhyung@gmail.com>,
        Paul Mackerras <paulus@samba.org>,
        Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH V2 1/9] perf tools: Fix symbol annotation for relocated
 kernel
Message-ID: <20140130181530.GC8098@ghostprotocols.net>
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Em Thu, Jan 30, 2014 at 03:12:32PM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Thu, Jan 30, 2014 at 03:08:23PM -0300, Arnaldo Carvalho de Melo escreveu:
> > Getting segfaults with:
>  
> > [acme@ssdandy linux]$ git log --oneline | head -10
> > c059c953531f perf tests: vmlinux-kallsyms test does not need to set up ref_reloc_sym
> > be2530836ebe perf symbols: Prevent the use of kcore if the kernel has moved
> > 9b2fd7840cb0 perf record: Get ref_reloc_sym from kernel map
> > bcf5e06a0c75 perf symbols: Add kallsyms__get_function_start()
> > 94591ed0963e perf machine: Add machine__get_kallsyms_filename()
> > 18923cddb839 perf symbols: Fix symbol annotation for relocated kernel
> 
> Program received signal SIGSEGV, Segmentation fault.
> perf_event__synthesize_kernel_mmap (tool=0x81fd20 <record>, process=0x42ad51 <process_synthesized_event>, machine=0x916380) at util/event.c:520
> 520		size = snprintf(event->mmap.filename, sizeof(event->mmap.filename),
> 521				"%s%s", mmap_name, kmap->ref_reloc_sym->name) + 1;
> (gdb) p mmap_name
> $4 = 0x7fffffffabd0 "[kernel.kallsyms]"
> (gdb) p kmap->ref_reloc_sym
> $5 = (struct ref_reloc_sym *) 0x0
> (gdb)

This is the buggy one:

[acme@ssdandy linux]$ perf record usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.018 MB perf.data (~770 samples) ]
[acme@ssdandy linux]$ git show 9b2fd7840cb0d23068bc97e08db46f57f41021fe
commit 9b2fd7840cb0d23068bc97e08db46f57f41021fe
Author: Adrian Hunter <adrian.hunter@intel.com>
Date:   Wed Jan 29 16:14:40 2014 +0200

    perf record: Get ref_reloc_sym from kernel map
    
    Now that ref_reloc_sym is set up when the kernel map is created, 'perf
    record' does not need to pass the symbol names to
    perf_event__synthesize_kernel_mmap() which can read the values needed
    from ref_reloc_sym directly.