Hi, How do we proceed with this?
I would especially be interested in the "patching" that you do in Guix. Maybe that would also be a suitable workaround for us on the Alpine side until this is sorted out properly. Greetings, Sören Sören Tempel <soe...@soeren-tempel.net> wrote: > Hi, > > Thanks for your feedback, comments below. > > Maxime Devos <maximede...@telenet.be> wrote: > > Long term, I think it would be ideal for Guile to decide upon a major > > version (and maybe even location, depending on the choices of the > > distro) at _compile_ time instead of runtime, not unlike how other > > compilers work. > > Sure, that could work too. > > > If the Guile module is being compiled with --rpath, it searches > > $CROSS_LIBRARY_PATH or $LIBRARY_PATH and encodes the full file name > > (/usr/lib/.../libguile-... or /gnu/store/.../lib/...) in the .go, > > which avoids some manual patching we have to do in Guix. > > What kind of manual patching do you do on Guix? Could you refer me to > the code for that? Maybe that's something we could also do on Alpine in > the meantime. > > > IIUC, the string-prefix? search is non-deterministic, which can make > > debugging complicated when multiple versions are installed. > > Well, on Linux readdir(3) file name order depends on the file system > implementation. Since the algorithm returns the first file with a > substring match, it depends on the readdir order. As long as the same > filesystem is used, it should be deterministic. > > > I think it would be better to bail out if there are multiple matches > > instead of a risk of guessing incorrectly. > > Many packages provide multiple .so files with different version > granularity so bailing out if there are multiple substring matches > doesn't really work. For example, for libgit2 I have the following files > installed on my system: > > $ ls /usr/lib/libgit2* > /usr/lib/libgit2.so.1.4 > /usr/lib/libgit2.so.1.4.4 > > Where the former is a symlink to the latter. However, it would be > possible to collect all substring matches and prioritize them according > to some algorithm (e.g. alphabetical order). This would also make the > algorithm independent of the readdir(3) order. > > > The prefixing behaviour is also not documented, so some documentation is > > needed in the manual. > > I can add some documentation if there is interest in merging this. > > > * Does it go scanning the dir even if libfoo.so could be found? > > Otherwise, there are some possible performance gains by checking for > > libfoo.so first -- consider the case where /usr/lib is huge. > > Yes, a fast path could be added though you probably really need to have > a lot of files installed in /usr/lib for this to be worth it. > > > * When doing (load-foreign-library "/gnu/store/.../libfoo.so") > > (absolute file name!), would it search for > > /gnu/store/.../libfoo.so.N? If so, that would be surprising, > > especially if libfoo.so.N exists. > > Yep, it does. I originally didn't want to modify the handling of > absolute paths but unfortunately during testing I noticed that Guile > extensions seem to be loaded with an absolute path and hence don't > work without the libfoo.so symlink [1]. > > > * If doing libfoo.so.N, will it search for libfoo.so.N.M? > > Yes, since libfoo.so.N is a prefix of libfoo.so.N.M. > > > * Does it only apply to the system paths, or also to > > GUILE_SYSTEM_EXTENSION_PATH, LTDL_LIBRARY_PATH and > > GUILE_EXTENSION_PATH? The latter would be surprising to me, as > > versioning is more of a system thing. > > If those paths are also searched using the load-foreign-library > procedure then they are affected by this change. Also, I am not a Guile > expert but on Alpine, Guile extensions such as guile-reader also ship > versioned sonames [1]. > > > * To test it, and avoid breaking things later with future changes to > > load-foreign-library, could some tests be added? > > Probably, though I am not familiar with the Guile test setup and there > don't seem to be any existing tests for foreign-library. > > > * Is this change desirable? I mean, this is an FFI API, so the ABI of > > the library is rather important. If a Guile module links to > > libfoo.so, and they had version N in mind, then it's important it > > doesn't link to N-1 or N+1 instead, because of ABI > > incompatibilities. As such, to me it seems _good_ that you got some > > errors, as now you get a reminder to explicitly state which ABI > > version is needed. (YMMV, and the mileage of the Guile maintainers > > might vary, etc.) > > In my experience, most languages which don't link against shared > libraries directly but instead load them at run-time don't hardcode ABI > versions (for example, refer to Python's ctypes.util.find_library). > Also, the current implementation of load-foreign-library does not force > you to specify an ABI version but instead loads whatever the libfoo.so > symlink refers to. > > > Also, this seems like a non-trivial change to me, so a copyright line > > might be in order, unless you did the copyright assignment. > > I didn't do any copyright assignment yet but if there is actually any > interest in merging this then I can do it once we agreed on changes to > the algorithm. > > Greetings, > Sören > > [1]: https://gitlab.alpinelinux.org/alpine/aports/-/issues/12783