rpm vs --compress-debug-sections=zlib

[Vít Ondruch]

Hi,

Recently, there have started to appear weird messages in the build
output of development snapshot of Ruby [1]:


```

... snip ...

+ /usr/lib/rpm/find-debuginfo.sh --strict-build-id -m --run-dwz
--dwz-low-mem-die-limit 10000000 --dwz-max-die-limit 110000000
/builddir/build/BUILD/ruby-2.4.0-r56693

... snip ...

extracting debug info from
/builddir/build/BUILDROOT/ruby-2.4.0-0.1.r56693.fc26.x86_64/usr/lib64/libruby.so.2.4.0
/usr/lib/rpm/debugedit:
/builddir/build/BUILDROOT/ruby-2.4.0-0.1.r56693.fc26.x86_64/usr/lib64/libruby.so.2.4.0:
DWARF version 0 unhandled
extracting debug info from
/builddir/build/BUILDROOT/ruby-2.4.0-0.1.r56693.fc26.x86_64/usr/bin/ruby-mri

... snip ...

dwz: ./usr/lib64/libruby.so.2.4.0.debug: DWARF version 0 unhandled

... snip ...

```


This was apparently introduced by upstream commit [2], which adds
"--compress-debug-sections=zlib" as one of linker options. What I
actually don't understand what are the implications of this.

* It seems that RPM cannot handle the compressed debug info properly,
does it also mean that the debuginfo is not stripped?

* Should I ask RPM guys to add support for this?

* Should I remove this flag? Should I ask upstream to make the
compression optional?


Vít



[1] http://koji.fedoraproject.org/koji/taskinfo?taskID=16383886

[2]
https://github.com/ruby/ruby/commit/a40d95c48fa7e7974feb294abca8af34e299d109

[Tom Hughes]

On 10/11/16 15:25, Vít Ondruch wrote:

>  This was apparently introduced by upstream commit [2], which adds
>  "--compress-debug-sections=zlib" as one of linker options. What I
>  actually don't understand what are the implications of this.
>
>  * It seems that RPM cannot handle the compressed debug info properly,
>  does it also mean that the debuginfo is not stripped?
>
>  * Should I ask RPM guys to add support for this?
>
>  * Should I remove this flag? Should I ask upstream to make the
>  compression optional? 
I'd say remove it - compressing the debug sections is horrible because 
it forces anything that wants to access the debug data to load it all in 
and decompress it rather than just reading what it needs.

Tom

-- 
Tom Hughes (tom(a)compton.nu)
http://compton.nu/

[Kevin Kofler]

Tom Hughes wrote:
>  I'd say remove it - compressing the debug sections is horrible
> because
>  it forces anything that wants to access the debug data to load it all in
>  and decompress it rather than just reading what it needs. 
In addition, it actually increases download sizes because RPMs and live 
images are xz-compressed, and xz compresses uncompressed data better than 
zlib-compressed data. The zlib compression is much poorer than xz 
compression, it just keeps xz from compressing things well.

        Kevin Kofler

[Vít Ondruch]

As a follow up, I opened ticket to add compressed debug section support
to RPM [1] and asked Ruby upstream to make this flag configurable [2].


Vít


[1] https://bugzilla.redhat.com/show_bug.cgi?id=1394759

[2] https://bugs.ruby-lang.org/issues/12934




Dne 10.11.2016 v 16:25 Vít Ondruch napsal(a):
>  Hi,
>
>  Recently, there have started to appear weird messages in the build
>  output of development snapshot of Ruby [1]:
>
>
>  ```
>
>  ... snip ...
>
>  + /usr/lib/rpm/find-debuginfo.sh --strict-build-id -m --run-dwz
>  --dwz-low-mem-die-limit 10000000 --dwz-max-die-limit 110000000
>  /builddir/build/BUILD/ruby-2.4.0-r56693
>
>  ... snip ...
>
>  extracting debug info from
>  /builddir/build/BUILDROOT/ruby-2.4.0-0.1.r56693.fc26.x86_64/usr/lib64/libruby.so.2.4.0
>  /usr/lib/rpm/debugedit:
>  /builddir/build/BUILDROOT/ruby-2.4.0-0.1.r56693.fc26.x86_64/usr/lib64/libruby.so.2.4.0:
>  DWARF version 0 unhandled
>  extracting debug info from
>  /builddir/build/BUILDROOT/ruby-2.4.0-0.1.r56693.fc26.x86_64/usr/bin/ruby-mri
>
>  ... snip ...
>
>  dwz: ./usr/lib64/libruby.so.2.4.0.debug: DWARF version 0 unhandled
>
>  ... snip ...
>
>  ```
>
>
>  This was apparently introduced by upstream commit [2], which adds
>  "--compress-debug-sections=zlib" as one of linker options. What I
>  actually don't understand what are the implications of this.
>
>  * It seems that RPM cannot handle the compressed debug info properly,
>  does it also mean that the debuginfo is not stripped?
>
>  * Should I ask RPM guys to add support for this?
>
>  * Should I remove this flag? Should I ask upstream to make the
>  compression optional?
>
>
>  Vít
>
>
>
>  [1] http://koji.fedoraproject.org/koji/taskinfo?taskID=16383886
>
>  [2]
>  https://github.com/ruby/ruby/commit/a40d95c48fa7e7974feb294abca8af34e299d109
>
>
>
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