Am Sun, 08 Apr 2012 21:08:52 +0200 schrieb "Iain Buclaw" <[email protected]>:
> I got asked whether there are any porting hints for phobos on > other architectures the other day from the debian GCC > maintainers. So I gathered this must be at least a dedicated > wiki or article to be written up on the subject. :) > > I know there are a few working on porting gdc and associated > libraries over to ARM (with my assistance from the compiler > side). So please tell, what are your experiences? Successes? > Failures? What tips would you give to someone wanting to port to > their own architecture? > > Regards > Iain (This is mostly about porting to a different C library. I don't remember many issues when porting to a different CPU architecture) Issues I hit with druntime: * Adapting the core.stdc bindings to something different than the currently supported C libraries sucks: The version blocks are sometimes completely wrong. For example Android's bionic is a C library based on BSD code, but running on Linux. As a result sometimes the version(FreeBSD) blocks apply for bionic, but sometimes the version(linux) blocks are right. I basically had to rewrite the complete core.stdc bindings. This is an issue because druntime and phobos do not distinguish between OS/Kernel and C library. * Wrong constants or macros in the C bindings are very hard to spot - you'll only notice those at runtime * When statically linking the phobos/druntime library you are no warned about missing symbols - For shared libraries -Wl,--no-undefined can be used, however, there are some issues with that as well: (http://stackoverflow.com/questions/2356168/force-gcc-to-notify-about-undefined-references-in-shared-libraries second answer) * Bionic just implements some functions as macros and never exports those as functions (htons, etc). Because of the last point it's easy to miss that Ideally all of the core.stdc bindings should be generated automatically. This is possible if we can run code (using offsetof, alignof, etc) but it's not that easy for cross compilation. I thought about hooking into the GCC C frontend to do that, but I had no time to look at it yet. * All those issues also apply to phobos, where phobos uses custom C bindings / extern(C) declarations. * I had to edit some stuff in std.stdio (because Android has no wide character/fwide support). Templates can be annoying in this case: some if(isOutputRange!T) chains hid an error in the IO code, it took me some time to find that problem. The reported error was completely misleading (cannot put dchar[] into LockingTextWriter or something) * When adding new, system specific code to a module and using selective imports, that may affect other modules (can't remember which compiler bug this was). This means that adding an import in one module might break another module on another architecture. * Porting the GC doesn't seem to be too difficult, but some care is needed to get stack scanning/TLS scanning right (If you have random crashes, it's either the GC not working(probably not scanning stack/tls) or fno-section-anchors missing) * Always use "-fno-section-anchors". It's not needed for simple code, but I was chasing a weird bug in derelict, till I realized I didn't compile derelict with "-fno-section-anchors". * Right now, issue 284 is a little annoying. At least unittest and phobos/druntime as shared libraries won't work at all till that's fixed. * AFAIK the unittests cannot be run when cross-compiling right now? * There might be more issues like this one where phobos is checking for a wrong status code: (https://github.com/D-Programming-Language/phobos/pull/487) * For systems where long double isn't available, fixing core.stdc.math is annoying. I have to implement a proper solution which works for all systems without long double. However, all that considered most issues are when interfacing C. The D code most of the time 'just works'.
