Re: [icu-design] debian: use of --disable-rename and ICU library sonames

[Andy H. <and...@gm...>]

On Tue, Jun 10, 2008 at 11:54 AM, Jay Berkenbilt <ej...@ql...> wrote:
>
> I'm the maintainer of the ICU packages for the debian GNU/Linux
> distribution.  A few months ago, George Rhoten had made a suggestion
> that I should be configuring ICU with the --disable-rename flag, and
> in preparation for creating the ICU 4.0 packages, I looked into to his
> suggestion and had some questions.  He reported to me that he is no
> longer working on ICU and suggested that I take this to the icu-design
> mailing list.  I have temporarily subscribed myself, and will
> summarize here.

It looks to me like your analysis of the questions surrounding ICU
renaming is correct.

> It also seems that, to guarantee binary
> compatibility, there are a number of other things developers have to
> do such as only using stable APIs and avoiding the C++ APIs.

This is absolutely true.

Running without renaming, and changing out the version of ICU behind
installed applications would involve a greater risk of instability.
The flip side is making available updated locale, language, Unicode &
data that comes with a new version of the library.

So it's not completely black and white, but I suspect continuing with
renaming is safest.  Let installed binary applications continue to run
with the ICU version they were built with.

  -- Andy

>
> Here is my reply to George Rhoten's original message, with his message
> quoted before it:
>
> -----------
>
> In February, you sent me the following:
>
> "George Rhoten" <gr...@gm...> wrote:
>
>> Hi Jay,
>>
>> I was noticing how Debian is building the ICU libraries, and I have
>> one suggestion.
>>
>> Instead of using the following in Debian's rules file:
>>
>> # specific to this package
>> l_CONFIGURE += --disable-samples --enable-static --enable-weak-threads
>>
>> you might want to consider using the following instead:
>>
>> # specific to this package
>> l_CONFIGURE += --disable-samples --enable-static --enable-weak-threads
>> --disable-renaming
>>
>> The ICU User's Guide
>> (http://www.icu-project.org/userguide/design.html#ICU_Binary_Compatibility)
>> mentions the --disable-renaming configure option for ensuring binary
>> compatibility between ICU releases.  We usually recommend that OS
>> vendors use this option.
>
> I was thinking about doing this for the 4.0 release, but I'm not sure
> it's really the right thing for Debian.  I hope you can clarify.  The
> documentation states that --disable-renaming prevents renaming of
> symbols such that binary compatibility can be obtained across
> releases.  However, the shared libraries are built with an soname
> based on the release.  There is therefore no way an executable linked
> with one version will run with another version unless someone makes
> extra symbolic links or otherwise messes around with the installed
> shared libraries.  It also seems that, to guarantee binary
> compatibility, there are a number of other things developers have to
> do such as only using stable APIs and avoiding the C++ APIs.  There is
> no way I can guarantee this among debian users or even among the
> packages that depend on debian.  It seems to me that the safest thing
> for debian would be to continue to enable renaming.  Even if we
> disable renaming, because the shared library sonames, we still won't
> get binary compatibility across releases even for those that follow
> the other guidelines.  Have I made an error in my analysis?  Please
> let me know.  Since the --disable-renaming and --enable-renaming
> versions aren't binary compatible with each other (if I understand
> correctly), I can't make this change until 4.0 anyway, and 4.0 will
> unfortunately be too late to make it into the upcoming Lenny release.
> (It's already too late for me to start a library transition with as
> many reverse dependencies as ICU.)  Either way, I'd like to make a
> decision on this before my initial upload of 4.0.  Thanks!
>
> -----------
>
> In response to the above, he sent the following reply:
>
>> Since I don't work on ICU anymore, you may want to bring up the
>> issue on the icu-design mailing list.  Maybe --disable-renaming can
>> be modified to remove the soname usage when the option is used.
>>
>> I know that Apple uses --disable-renaming so that they can
>> distribute ICU, but they customize ICU in a way that creates a
>> single libicucore library.  AIX also distributes ICU, and I believe
>> they use --disable-renaming; however, the soname concept isn't quite
>> the same on that OS.
>>
>> It's probably better to discuss this before the d03 release.  That
>> way, any required changes may be able to make the 4.0 release.
>
> I'd welcome any suggestions on this point.  Unless I hear otherwise,
> my intention is to continue not using --disable-renaming and to
> continue forcing an ICU transition for each new release of ICU that
> changes the soname.  This happens infrequently enough that it's not
> that big a deal, and I've recently taken version number information
> out of the development package version so that the transitions can be
> largely automated.  In order for me to be willing to use
> --disable-renaming, I would need to believe that it is quite safe to
> do so.  Otherwise, keeping track of which applications need to be
> rebuilt when ICU changes will be problematic.  Thanks!
>
> --
> Jay Berkenbilt <ej...@ql...>
>
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