linux-kernel - Re: [PATCH 01/42] perf tools: Support to read compressed module from build-id cache

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Date:	Tue, 3 Feb 2015 00:03:36 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 01/42] perf tools: Support to read compressed module from
 build-id cache

On Fri, Jan 30, 2015 at 11:32 PM, Jiri Olsa <jolsa@...hat.com> wrote:
> On Thu, Jan 29, 2015 at 05:06:42PM +0900, Namhyung Kim wrote:
>> The commit c00c48fc6e6e ("perf symbols: Preparation for compressed
>> kernel module support") added support for compressed kernel modules
>> but it only supports system path DSOs.  When a dso is read from
>> build-id cache, its filename doesn't end with ".gz" but has build-id.
>> In this case, we should fallback to the original dso->name.
>>
>> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>> ---
>>  tools/perf/util/symbol-elf.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
>> index 06fcd1bf98b6..b24f9d8727a8 100644
>> --- a/tools/perf/util/symbol-elf.c
>> +++ b/tools/perf/util/symbol-elf.c
>> @@ -574,13 +574,16 @@ static int decompress_kmodule(struct dso *dso, const char *name,
>>       const char *ext = strrchr(name, '.');
>>       char tmpbuf[] = "/tmp/perf-kmod-XXXXXX";
>>
>> -     if ((type != DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE_COMP &&
>> -          type != DSO_BINARY_TYPE__GUEST_KMODULE_COMP) ||
>> -         type != dso->symtab_type)
>> +     if (type != DSO_BINARY_TYPE__SYSTEM_PATH_KMODULE_COMP &&
>> +         type != DSO_BINARY_TYPE__GUEST_KMODULE_COMP &&
>> +         type != DSO_BINARY_TYPE__BUILD_ID_CACHE)
>>               return -1;
>
> hum, is it possible the type == DSO_BINARY_TYPE__BUILD_ID_CACHE could get in here?
>
>
> ---
>         for (i = 0; i < DSO_BINARY_TYPE__SYMTAB_CNT; i++) {
>                 struct symsrc *ss = &ss_[ss_pos];
>                 bool next_slot = false;
>
>                 enum dso_binary_type symtab_type = binary_type_symtab[i];
>
>                 if (!dso__is_compatible_symtab_type(dso, kmod, symtab_type))
>                         continue;
>
> ---             ^^^ this check should rule out buildid symtab_type for kmod dso?

AFAICS symtab_type of BUILD_ID_CACHE always returns true in this function.


>
>                 symsrc__init(
>
>
> I wonder wether we should set special type from compressed binaries (as of now),
> or instead try to decompress anything that looks like it's compressed ;-)
> it seems more to be more generic and could simplify the code..

I don't know.  But it seems only kernel modules are compressed now.
If user-level dso also supports compression, we need to think about it
again..

Thanks,
Namhyung
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