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Wine MinGW system libraries

Hello all,

I'm a contributor to the Wine project. To summarize the following mail, Wine needs special versions of some of its normal dependencies, such as libfreetype and libgnutls, built using the MinGW cross-compiler, and I'm sending out a mail to major distributions in order to get some feedback from our packagers on how these should be built and packaged.

For a long time Wine has built all of its Win32 libraries (DLLs and EXEs) as ELF binaries. For various reasons related to application compatibility, we have started building our binaries as PE instead, using the MinGW cross-compiler. It is our intent to expand this to some of our dependencies as well. The list of dependencies that we intend to build using MinGW is not quite fixed yet, but we expect it to include and be mostly limited to the following:

* libvkd3d
* libFAudio
* libgnutls
* zlib (currently included via manual source import)
* libmpg123
* libgsm
* libpng
* libjpeg-turbo
* libtiff
* libfreetype
* liblcms2
* jxrlib

and dependencies of the above packages (not including CRT dependencies, which Wine provides).

There is currently some internal discussion about how these dependencies should be built and linked. There are essentially three questions I see that need to be resolved, and while these resolutions have a significant impact on the Wine building and development process, they also have an impact on distributions, and accordingly I'd like to get input from our packagers to ensure that their considerations are accurately taken into account.

(1) Should we build via source import, or link statically, or dynamically?

Source imports are dispreferred by Debian [1], on the grounds that they cause duplication of libraries on disk and in memory, and make it harder to handle security updates. They also make building and bisecting harder. Static libraries don't seem to be expressly discouraged, but share most of the same downsides (see also [2]).

Note however that if they are linked dynamically, we need to make sure that we load our packages instead of MinGW builds of open-source libraries with applications ship with. There's some internal discussion about whether this is possible while using "stock" builds of MinGW libraries, but, due to the way the Win32 loader works, we will probably need to compile each library, and its dependencies, with a separate, wine-specific name, e.g. "libwinefreetype-6.dll" and "libwineharfbuzz.dll". For a detailed explantion see footnote [3]. Note that all we actually need to change is the name; we don't need to patch the source.

Accordingly, although static linking and source imports are generally disprefered, it may quite likely be preferable in our case. We don't get the benefits of on-disk deduplication, since Wine is essentially the only piece of software which needs these libraries.

(2) If we use dynamic libraries, should dependencies be included in the main wine package, or packaged separately?

This is mostly a question for packagers, although it also relates to (3).

I expect that Debian will want to answer "packaged separately" here, on the grounds that this lets them update (say) Wine's libgnutls separately, and in sync with ELF libgnutls, if some security fix is needed. There is a snag, though: we need libraries to be copied into the prefix (there's some internal effort to allow using something like symlinks instead, but this hard and not done yet). Normally we perform this copy every time Wine is updated, but if Wine and its dependencies aren't updated on the same schedule, we may end up loading an old version of a dependency in the prefix.

(3) If dependencies are packaged separately, should Wine build them as part of its build tree (e.g. using submodules), or find and link (statically or dynamically) to existing binaries?

Linking to existing binaries is generally preferable: it avoids duplication on disk; it reduces compile times when compiling a single package from source (especially the first time). However, we aren't going to benefit from on-disk duplication. And, most importantly, unlike with ELF dependencies, there is no standardized way to locate MinGW libraries—especially if it comes to Wine-specific libraries. We would need a way for Wine's configure script to find these packages—and ideally find them automatically, or else fall back to a submodule-based approach.

If we rely on distributions to provide our dependencies, the best idea I have here would be something like a x86_64-w64-mingw32-pkg-config (Fedora actually already ships this, but I think Fedora is the only one). And if we use shared libraries rather than static, things get worse: we need to know the exact path of each library and its dependencies at runtime so that we can copy (or symlink) them into a user's WINEPREFIX. For ELF this is the job of ld.so. For MinGW there is no standardized install location across distributions.

For what it's worth, the current proposed solution (which has the support of the Wine maintainer) involves source imports and submodules. There's probably room for changing our approach even after things are committed, but I'd still like to get early feedback from distributions, and make sure that their interests are accurately represented, before we commit.


[1] https://www.debian.org/doc/debian-policy/ch-source.html#embedded-code-copies

[2] https://wiki.debian.org/StaticLinking

[3] The basic problem is that applications can and often do ship with PE builds of cross-platform libraries. These libraries can be ahead of Wine's system libraries, behind them, or even built with custom patches. Accordingly we really don't want to load "our" freetype in place of "their" freetype, or "theirs" in place of "ours". But because of the way the Win32 loader works, you can generally only have one DLL of a given name loaded in a process, and further attempts to dlopen() [as it were] "libfreetype-6.dll" will return the handle to the already loaded library, potentially breaking either Wine or the application. There *may* be ways we can hack around this internally, but it's not clear that it's feasible yet, and so it's probably best to assume that we'll need special builds of dynamic libraries.

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