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Subject: Re: [PATCH v3 3/7 UPDATE] perf tools: Add option for the path of
 buildid dsos under symfs
To: David Ahern <dsahern@gmail.com>, <peterz@infradead.org>,
        <mingo@redhat.com>, <acme@kernel.org>,
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        <penberg@kernel.org>
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From: Hekuang <hekuang@huawei.com>
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Date: Mon, 16 May 2016 09:30:22 +0800
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在 2016/5/14 22:43, David Ahern 写道:
> On 5/14/16 2:19 AM, He Kuang wrote:
>> In the cross-platform perf record/script scenario, we need vdsos in
>> buildid-cache dir and other libs in symfs dir at the same time. For
>> the reason that to have every single file opened by perf is relative
>> to symfs dirctory, perf skips the buildid dir if symfs is given.
>>
>> This patch references the buildid dir under symfs if '--symfs' is
>> used, and adds new option '--dso-prefix' to specify the subdir path in
>> symfs which contains the buildid dsos.
>
> In the previous version of this patch you just wanted to drop the 
> symfs check. That means there is a path that perf searches for buildid 
> files and reading it worked for you. Why is adding symsfs to that path 
> not enough? ie., Why do you need to specify a different location under 
> the symfs?
>
In previous patch, I use 'perf buildid-cache -a' to add vdso
binary into the HOST buildid dir.

Currently, $(BUILDID_ROOT)/.debug/.buildid has a directory
structure organized by the buildid value, like this:

  .build-id
  - 3a
  |    e5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd
  - 84
       dbd75729adba57cc42f5544b25de571c0c8731

perf searchs for buildid binaries by the buildid value.

And symfs is a normal file tree and perf searchs for binaryies
by the file name.

  lib
  - libc.so
  - ld.so

Tt's inappropriate to add symfs to .build-id dir becuase they
have different dirctory structure and perf searchs for them by
differnt ways.

So in this patch I add .buildid to symfs and got dirctory tree
like this:

  symfs
  - $(DSO_PREFIX)
      - .build-id
            - 3a
            - 84
  - libc.so
  - ld.so

Thanks