Re: [RFC] Unify KVM kernel-space and user-space code into a single project

Arnaldo Carvalho de Melo
2010-03-24T18:27:05Z

Em Wed, Mar 24, 2010 at 08:20:10PM +0200, Avi Kivity escreveu:
> On 03/24/2010 07:47 PM, Arnaldo Carvalho de Melo wrote:
>> Em Wed, Mar 24, 2010 at 06:09:30PM +0200, Avi Kivity escreveu:
>>
>>> Doesn't perf already has a dependency on naming conventions for finding
>>> debug information?
>>>
>> It looks at several places, from most symbol rich (/usr/lib/debug/, aka
>> -debuginfo packages, where we have full symtabs) to poorest (the
>> packaged binary, where we may just have a .dynsym).
>>
>> In an ideal world, it would just get the build-id (a SHA1 cookie that is
>> in an ELF session inserted in every binary (aka DSOs), kernel module,
>> kallsyms or vmlinux file) and use that to look first in a local cache
>> (implemented in perf for a long time already) or in some symbol server.
>>
>> For instance, for a random perf.data file I collected here in my machine
>> I have:
>>
>> [acme@doppio linux-2.6-tip]$ perf buildid-list | grep libpthread
>> 5c68f7afeb33309c78037e374b0deee84dd441f6 /lib64/libpthread-2.10.2.so
>> [acme@doppio linux-2.6-tip]$
>>
>> So I don't have to access /lib64/libpthread-2.10.2.so directly, nor some
>> convention to get a debuginfo in a local file like:
>>
>> /usr/lib/debug/lib64/libpthread-2.10.2.so.debug
>>
>> Instead the tools look at:
>>
>> [acme@doppio linux-2.6-tip]$ l ~/.debug/.build-id/5c/68f7afeb33309c78037e374b0deee84dd441f6
>> lrwxrwxrwx 1 acme acme 73 2010-01-06 18:53 /home/acme/.debug/.build-id/5c/68f7afeb33309c78037e374b0deee84dd441f6 -> ../../lib64/libpthread-2.10.2.so/5c68f7afeb33309c78037e374b0deee84dd441f6*
>>
>> To find the file for that specific build-id, not the one installed in my
>> machine (or on the different machine, of a different architecture) that
>> may be completely unrelated, a new one, or one for a different arch.

> Thanks. I believe qemu could easily act as a symbol server for this use
> case.

Agreed, but it doesn't even have to :-)

We just need to get the build-id in the PERF_RECORD_MMAP event somehow
and then get this symbol from elsewhere, say the same DVD/RHN
channel/Debian Repository/embedded developer toolkit image not
stripped/whatever.

Or it may already be in the local cache from last week's perf report
session :-)

- Arnaldo