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List: ubuntu-devel
Subject: Re: Symbols files for C++ libraries for Ubuntu main
From: Sebastien Bacher <seb128 () ubuntu ! com>
Date: 2023-06-09 12:27:02
Message-ID: 67216a04-e786-8780-c237-b6c2e0071d68 () ubuntu ! com
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Hey there,
We had been struggling with a few of those cases recently in desktop and
I was going to send an email about the topic then checking the archive I
found back that discussion that I had forgotten about.
I would like to ask if there is any chance the MIR team would reconsider
their position on the topic (at least until the day we have a somewhat
working solution we can use)?
Here is why. Taking a recent example from desktop and describing the
experience on one package where we basically had to go through those steps
1. We added a symbols to libcupsfilters as part of the MIR promotion
https://git.launchpad.net/ubuntu/+source/libcupsfilters/commit/debian/libcupsfilters2.symbols?h=applied/ubuntu/devel&id=c5821fe0
The build failed on armhf because dh_makeshlibs report symbols on armhf
which do not existing on amd64
https://launchpadlibrarian.net/647850924/buildlog_ubuntu-lunar-armhf.libcupsfilters_2.0~b2-0ubuntu4_BUILDING.txt.gz
which also included those types of changes
- _Znam@Base 2.0~b2-0ubuntu3
+ _Znaj@Base 2.0~b2-0ubuntu4
+#MISSING: 2.0~b2-0ubuntu4# _Znam@Base 2.0~b2-0ubuntu3
I personally don't understand why we have those symbols existing on
armhf which don't exist on amd64. Nor why _Znam@Base is becoming
_Znaj@Base nor how we are supposed to handle such cases
2. I tried to help getting that resolved with that upload
http://launchpadlibrarian.net/647856580/libcupsfilters_2.0~b2-0ubuntu4_2.0~b2-0ubuntu5.diff.gz
Which basically add the symbols showing a new on the armhf as
'(optional)' and also listed those that changes as optional in their
different variants
3. similar round for riscv64
http://launchpadlibrarian.net/647865001/libcupsfilters_2.0~b2-0ubuntu5_2.0~b2-0ubuntu6.diff.gz
4. doing those tweaks need to be done manually since it's not only
applying the diff but also adding optional keyword at places, I got one
wrong and it failed to build again
add one more symbol specific to risvc
http://launchpadlibrarian.net/647875197/libcupsfilters_2.0~b2-0ubuntu6_2.0~b2-0ubuntu7.diff.gz
5. still failed, I had to add another bunch of symbols from the previous
build log
http://launchpadlibrarian.net/647896999/libcupsfilters_2.0~b2-0ubuntu7_2.0~b2-0ubuntu8.diff.gz
Which finally got us a working build.
I understand the motivation for wanting a symbol file but I agree with
what Robie, what's the benefit. In that case we spent a few hours to end
up with a .symbols which as over 150 '(optional)' entries, that doesn't
protect us much better than just not having a .symbols or using -c0 but
still has a high cost.
And from experience it is likely that following the next toolchain
update the .symbols will not match anymore and that those of us who will
end up having to fix the package build will not understand why and just
end up applying the diff proposed by dpkg-gensymbols.
Checking on the Debian side, https://wiki.debian.org/UsingSymbolsFiles
has a 'C++ libraries' section which start by this statement written in
bold style
> For C++ libraries it is often better not to ship symbols files.
Which means we will often fail at upstreaming such improvements to
Debian and will have to increase our delta. And I don't blame them, I'm
not even sure how to deal with the 'the symbols change between
architectures' out of throwing builds to a ppa to get results and
iterate and Debian doesn't have the ppa option...
Cheers,
Sebastien Bacher
Le 22/05/2018 à 18:25, Robie Basak a écrit :
> On Fri, May 18, 2018 at 08:29:13PM +0200, Matthias Klose wrote:
> > I completely disagree. Replacing a somehow suboptimal check with no
> > check is not an option.
> On Fri, May 18, 2018 at 08:22:55PM +0100, Dimitri John Ledkov wrote:
> > IMHO symbols files should be mandatory for any new libraries
> > introduced in the archive.
> >
> > And we should assert symbols files for everything in main, and fix all
> > the things.
> >
> > It's 2018, and we really ought to have sensible and strict symbols
> > files.
> Both of these statements on their own state that we must do this work
> but don't explain why this is of benefit to Ubuntu. I feel that you need
> to justify your position rather than just stating it.
>
> Can you provide examples of where maintaining this delta has actually
> helped make Ubuntu better, in the specific case that C++ symbols are
> being maintained by Ubuntu in a delta that Debian and upstream have
> declined to adopt or postponed adopting? Without examples, we're not
> really in a position to assess the trade-off of extra work vs. benefit
> to Ubuntu. I don't think we should be maintaining delta unless the
> benefit can be articulated and justified.
>
> Separately, I question whether it's in the interest of our project to
> spend time on maintaining a quality improvement indefinitely if Debian
> and/or upstream decline to take it, and if that particular improvement
> is not a high level goal of our project.
>
> Thanks,
>
> Robie
>
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<p>Hey there,</p>
<p>We had been struggling with a few of those cases recently in
desktop and I was going to send an email about the topic then
checking the archive I found back that discussion that I had
forgotten about.<br>
</p>
I would like to ask if there is any chance the MIR team would
reconsider their position on the topic (at least until the day we
have a somewhat working solution we can use)?<br>
<p><br>
Here is why. Taking a recent example from desktop and describing
the experience on one package where we basically had to go through
those steps</p>
<p>1. We added a symbols to libcupsfilters as part of the MIR
promotion<br>
<a class="moz-txt-link-freetext"
href="https://git.launchpad.net/ubuntu/+source/libcupsfilters/commit/debian/libcupsfil \
ters2.symbols?h=applied/ubuntu/devel&id=c5821fe0">https://git.launchpad.net/ubuntu \
/+source/libcupsfilters/commit/debian/libcupsfilters2.symbols?h=applied/ubuntu/devel&id=c5821fe0</a></p>
<p>The build failed on armhf because dh_makeshlibs report symbols on
armhf which do not existing on amd64<br>
<a class="moz-txt-link-freetext"
href="https://launchpadlibrarian.net/647850924/buildlog_ubuntu-lunar-armhf.libcupsfilt \
ers_2.0~b2-0ubuntu4_BUILDING.txt.gz">https://launchpadlibrarian.net/647850924/buildlog_ubuntu-lunar-armhf.libcupsfilters_2.0~b2-0ubuntu4_BUILDING.txt.gz</a><br>
<br>
which also included those types of changes<br>
</p>
<pre>- _Znam@Base 2.0~b2-0ubuntu3
+ _Znaj@Base 2.0~b2-0ubuntu4
+#MISSING: 2.0~b2-0ubuntu4# _Znam@Base 2.0~b2-0ubuntu3
</pre>
<p>I personally don't understand why we have those symbols existing
on armhf which don't exist on amd64. Nor why _Znam@Base is
becoming _Znaj@Base nor how we are supposed to handle such cases<br>
<br>
2. I tried to help getting that resolved with that upload<br>
<a class="moz-txt-link-freetext"
href="http://launchpadlibrarian.net/647856580/libcupsfilters_2.0~b2-0ubuntu4_2.0~b2-0u \
buntu5.diff.gz">http://launchpadlibrarian.net/647856580/libcupsfilters_2.0~b2-0ubuntu4_2.0~b2-0ubuntu5.diff.gz</a></p>
<p>Which basically add the symbols showing a new on the armhf as
'(optional)' and also listed those that changes as optional in
their different variants<br>
</p>
<p>3. similar round for riscv64</p>
<p><a class="moz-txt-link-freetext" \
href="http://launchpadlibrarian.net/647865001/libcupsfilters_2.0~b2-0ubuntu5_2.0~b2-0u \
buntu6.diff.gz">http://launchpadlibrarian.net/647865001/libcupsfilters_2.0~b2-0ubuntu5_2.0~b2-0ubuntu6.diff.gz</a></p>
<p>4. doing those tweaks need to be done manually since it's not
only applying the diff but also adding optional keyword at places,
I got one wrong and it failed to build again</p>
<p>add one more symbol specific to risvc<br>
<a class="moz-txt-link-freetext" \
href="http://launchpadlibrarian.net/647875197/libcupsfilters_2.0~b2-0ubuntu6_2.0~b2-0u \
buntu7.diff.gz">http://launchpadlibrarian.net/647875197/libcupsfilters_2.0~b2-0ubuntu6_2.0~b2-0ubuntu7.diff.gz</a></p>
<p>5. still failed, I had to add another bunch of symbols from the
previous build log<br>
<br>
<a class="moz-txt-link-freetext" \
href="http://launchpadlibrarian.net/647896999/libcupsfilters_2.0~b2-0ubuntu7_2.0~b2-0u \
buntu8.diff.gz">http://launchpadlibrarian.net/647896999/libcupsfilters_2.0~b2-0ubuntu7_2.0~b2-0ubuntu8.diff.gz</a></p>
<p>Which finally got us a working build.</p>
<p><br>
</p>
<p>I understand the motivation for wanting a symbol file but I agree
with what Robie, what's the benefit. In that case we spent a few
hours to end up with a .symbols which as over 150 '(optional)'
entries, that doesn't protect us much better than just not having
a .symbols or using -c0 but still has a high cost. <br>
And from experience it is likely that following the next toolchain
update the .symbols will not match anymore and that those of us
who will end up having to fix the package build will not
understand why and just end up applying the diff proposed by
dpkg-gensymbols.</p>
<p>Checking on the Debian side,
<a class="moz-txt-link-freetext" \
href="https://wiki.debian.org/UsingSymbolsFiles">https://wiki.debian.org/UsingSymbolsFiles</a> \
has a 'C++ libraries' section which start by this statement written in bold \
style<br> <br>
> For C++ libraries it is often better not to ship symbols
files. <br>
</p>
<p>Which means we will often fail at upstreaming such improvements
to Debian and will have to increase our delta. And I don't blame
them, I'm not even sure how to deal with the 'the symbols change
between architectures' out of throwing builds to a ppa to get
results and iterate and Debian doesn't have the ppa option...<br>
<br>
Cheers,<br>
Sebastien Bacher<br>
</p>
<div class="moz-cite-prefix">Le 22/05/2018 à 18:25, Robie Basak a
écrit :<br>
</div>
<blockquote type="cite"
cite="mid:20180522162522.GE18577@mal.justgohome.co.uk">
<pre class="moz-quote-pre" wrap="">On Fri, May 18, 2018 at 08:29:13PM +0200, \
Matthias Klose wrote: </pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">I completely disagree. Replacing a \
somehow suboptimal check with no check is not an option.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
On Fri, May 18, 2018 at 08:22:55PM +0100, Dimitri John Ledkov wrote:
</pre>
<blockquote type="cite">
<pre class="moz-quote-pre" wrap="">IMHO symbols files should be mandatory for \
any new libraries introduced in the archive.
And we should assert symbols files for everything in main, and fix all
the things.
It's 2018, and we really ought to have sensible and strict symbols
files.
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">
Both of these statements on their own state that we must do this work
but don't explain why this is of benefit to Ubuntu. I feel that you need
to justify your position rather than just stating it.
Can you provide examples of where maintaining this delta has actually
helped make Ubuntu better, in the specific case that C++ symbols are
being maintained by Ubuntu in a delta that Debian and upstream have
declined to adopt or postponed adopting? Without examples, we're not
really in a position to assess the trade-off of extra work vs. benefit
to Ubuntu. I don't think we should be maintaining delta unless the
benefit can be articulated and justified.
Separately, I question whether it's in the interest of our project to
spend time on maintaining a quality improvement indefinitely if Debian
and/or upstream decline to take it, and if that particular improvement
is not a high level goal of our project.
Thanks,
Robie
</pre>
<br>
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</blockquote>
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