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

[Jay B. <ej...@ql...>]

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.

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...>