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Old 02-24-2012, 09:11 PM
Sami Liedes
 
Default Bug#661193: linux-tools-3.2: perf fails to annotate code with separate debug info under some conditions

Package: linux-tools-3.2
Version: 3.2.1-2
Severity: normal

Hi!

perf report does not show source code lines (annotation) for some
binaries with separate debug information if those build-id's have been
cached in perf's build-id cache. This is true for at least those
packages whose debug symbols are installed in
/usr/lib/debug/path/binary and not in
/usr/lib/debug/.build-id/.../$hash. For example, e2fslibs, e2fsprogs
and I believe very many others packages are affected by this (the
mentioned packages even after fixing their -dbg packages per #661071).

This manifests with the following symptoms. If you want to test this,
I suggest either waiting for a fix for #661071 to be uploaded or to
choose a different package from e2fsprogs and its corresponding -dbg
package (but not one where the -dbg package has files in the .build-id
directory):

------------------------------------------------------------
1. Compile a package with separate debug info (so that you have the
sources available actually) and install both the package and the -dbg
package. Use a binary from the package in place of dumpe2fs in
following steps.

2. Run perf record -g dumpe2fs $some_fs_image

3. Run perf annotate

NOTE: functions in e.g. libext2fs.so.2.4 or in dumpe2fs are not
annotated with source code lines

4. run perf buildid-list. Note that it lists binaries for those
non-annotated functions. Either find the file in the
~/.debug/.build-id directory tree, or investigate using
perf annotate -vv (grep for "Executing:") where the file file
resides.

5. Note that the file you found is a copy of the binary or the library
in question, *not* a copy of the relevant file from /usr/lib/debug.
The objdump command that perf reports executing does not annotate it
with source code lines. If you try that same line but replace the
filename with the path to the actual binary, objdump knows where to
find the debug info and does annotate it.

6. mv perf.data perf.data.tmp

7. perf record -g ls

(this step is important because it empties the build-id cache and
populates it with objects needed for the ls execution; turns out perf
handles annotating fine once the relevant object is no longer in the
build-id cache)

8. perf annotate -i perf.data.tmp

NOTE: the functions that were unannotated in step 3 in that old
perf.data are now correctly annotated with source code.
------------------------------------------------------------

I think the actual bug is that, for some reason, in step 2 perf record
copies the non-debug version to the build-id cache instead of the
debug version. I have not investigated why this happens.

I also tried to remove the wrong file from the build-id cache and
re-add the correct one with perf buildid-cache -v
--remove=1a22c5f5c7a51ede62d01eeba1de59c15e7c9325; perf buildid-cache
--add=/path/to/file, but for some reason I couldn't get that --remove=
command to actually remove anything from the cache.

Sami


-- System Information:
Debian Release: wheezy/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)

Kernel: Linux 3.2.4 (SMP w/8 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash

Versions of packages linux-tools-3.2 depends on:
ii libc6 2.13-26
ii libdw1 0.152-1+b1
ii libelf1 0.152-1+b1
ii libnewt0.52 0.52.14-8
ii libperl5.14 5.14.2-7
ii libpython2.7 2.7.2-13
ii libslang2 2.2.4-6
ii perl 5.14.2-7
ii python 2.7.2-10

Versions of packages linux-tools-3.2 recommends:
ii linux-base 3.4

Versions of packages linux-tools-3.2 suggests:
pn linux-doc-3.2 <none>

-- no debconf information
 
Old 02-26-2012, 03:37 AM
Ben Hutchings
 
Default Bug#661193: linux-tools-3.2: perf fails to annotate code with separate debug info under some conditions

Here's a bug report on perf; I don't think there's anything I can add to
Sami's explanation.

Ben.

On Sat, 2012-02-25 at 00:11 +0200, Sami Liedes wrote:
> Package: linux-tools-3.2
> Version: 3.2.1-2
> Severity: normal
>
> Hi!
>
> perf report does not show source code lines (annotation) for some
> binaries with separate debug information if those build-id's have been
> cached in perf's build-id cache. This is true for at least those
> packages whose debug symbols are installed in
> /usr/lib/debug/path/binary and not in
> /usr/lib/debug/.build-id/.../$hash. For example, e2fslibs, e2fsprogs
> and I believe very many others packages are affected by this (the
> mentioned packages even after fixing their -dbg packages per #661071).
>
> This manifests with the following symptoms. If you want to test this,
> I suggest either waiting for a fix for #661071 to be uploaded or to
> choose a different package from e2fsprogs and its corresponding -dbg
> package (but not one where the -dbg package has files in the .build-id
> directory):
>
> ------------------------------------------------------------
> 1. Compile a package with separate debug info (so that you have the
> sources available actually) and install both the package and the -dbg
> package. Use a binary from the package in place of dumpe2fs in
> following steps.
>
> 2. Run perf record -g dumpe2fs $some_fs_image
>
> 3. Run perf annotate
>
> NOTE: functions in e.g. libext2fs.so.2.4 or in dumpe2fs are not
> annotated with source code lines
>
> 4. run perf buildid-list. Note that it lists binaries for those
> non-annotated functions. Either find the file in the
> ~/.debug/.build-id directory tree, or investigate using
> perf annotate -vv (grep for "Executing:") where the file file
> resides.
>
> 5. Note that the file you found is a copy of the binary or the library
> in question, *not* a copy of the relevant file from /usr/lib/debug.
> The objdump command that perf reports executing does not annotate it
> with source code lines. If you try that same line but replace the
> filename with the path to the actual binary, objdump knows where to
> find the debug info and does annotate it.
>
> 6. mv perf.data perf.data.tmp
>
> 7. perf record -g ls
>
> (this step is important because it empties the build-id cache and
> populates it with objects needed for the ls execution; turns out perf
> handles annotating fine once the relevant object is no longer in the
> build-id cache)
>
> 8. perf annotate -i perf.data.tmp
>
> NOTE: the functions that were unannotated in step 3 in that old
> perf.data are now correctly annotated with source code.
> ------------------------------------------------------------
>
> I think the actual bug is that, for some reason, in step 2 perf record
> copies the non-debug version to the build-id cache instead of the
> debug version. I have not investigated why this happens.
>
> I also tried to remove the wrong file from the build-id cache and
> re-add the correct one with perf buildid-cache -v
> --remove=1a22c5f5c7a51ede62d01eeba1de59c15e7c9325; perf buildid-cache
> --add=/path/to/file, but for some reason I couldn't get that --remove=
> command to actually remove anything from the cache.
>
> Sami


--
Ben Hutchings
Lowery's Law:
If it jams, force it. If it breaks, it needed replacing anyway.
 

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