While dealing with <https://bugs.gentoo.org/show_bug.cgi?id=393471> I
started discussing with developers working on libjpeg-turbo support in
WebKit, and I learned that despite
<http://archives.gentoo.org/gentoo-dev/msg_e67bedf25dd178ec09a325a1220724e6.xml>
libjpeg-turbo is not necessarily binary compatible with libjpeg, and
even with different versions of itself.

Here's why. See
<http://libjpeg-turbo.svn.sourceforge.net/viewvc/libjpeg-turbo/trunk/libjpeg.txt?revision=299&view=markup>
and search for "as a shared library". I'll paste the relevant quote here
anyway:

> While you can build the JPEG library as a shared library if the whim strikes
> you, we don't really recommend it.  The trouble with shared libraries is that
> at some point you'll probably try to substitute a new version of the library
> without recompiling the calling applications.  That generally doesn't work
> because the parameter struct declarations usually change with each new
> version.  In other words, the library's API is *not* guaranteed binary
> compatible across versions; we only try to ensure source-code compatibility.

The particular problem with www-client/chromium is caused by
<http://trac.webkit.org/changeset/101286/trunk/Source/WebCore/platform/image-decoders/jpeg/JPEGImageDecoder.cpp>
which sort of "hardcodes" in the compiled binary whether it was compiled
against libjpeg-turbo with swizzle support (whatever that is) or not.

The real problem here is that with above "no guarantee" of binary
compatibility such a solution may be considered legitimate, especially
that for e.g. Google Chrome the bundled copy of libjpeg-turbo is always
used.

What do you guys think we should do with this on the Gentoo side? At
this moment I've just reverted the mentioned change in
www-client/chromium ebuild, but it's not feasible to keep a local patch
too long (it needs rebasing too often).

I was thinking about changing SONAMES, which would trigger rebuilds make
things work, but then don't we rely on specific libjpeg SONAMES for
binary-only software to work? Or does such binary-only software just use
libjpeg-6b?

Are there some other solutions we could apply on the Gentoo side? The
main point here is that Chromium upstream considers
<http://trac.webkit.org/changeset/101286/trunk/Source/WebCore/platform/image-decoders/jpeg/JPEGImageDecoder.cpp>
a legitimate change, and based on the referenced
<http://libjpeg-turbo.svn.sourceforge.net/viewvc/libjpeg-turbo/trunk/libjpeg.txt?revision=299&view=markup>
disclaimer about no guarantee of binary compatibility, I think it makes
sense.