Can't link dub with i686 LDC 0.15.1

[mihails-strasuns]

Have tried to package dub (release 0.9.22) built with LDC in shared library mode:

    cmake \
    -DCMAKE_SKIP_RPATH=ON \
    -DCMAKE_INSTALL_PREFIX=/usr \
    -DINCLUDE_INSTALL_DIR=/usr/include/dlang/ldc \
    -DBUILD_SHARED_LIBS=ON \
    ..
    make

Works with no issues on x64_86 systems, but on i686 there is a linker failure:

/usr/lib/libldruntime-debug.so: undefined reference to `__mulodi4'
collect2: error: ld returned 1 exit status

Any ideas?

[dnadlinger]

The issue probably is in the core.checkedint.mul… implementation for 64 bit types. We forward to the LLVM intrinsic here, but apparently, it requires runtime support that is not found in libgcc, but only in the LLVM compiler_rt: http://llvm.org/bugs/show_bug.cgi?id=14469

If this is indeed the issue (didn't check), I'm not sure why the unit tests for the module pass on Travis, though. Apparently, we aren't running any 32 bit shared library tests (shudder), but one would expect the same issue to occur on static builds too.

[mihails-strasuns]

If this is the case, is there anything I can do to workaround this issue as a packager?

[dnadlinger]

I don't think so, it is something for us to fix in the next point release. If my suspicion regarding the root cause is correct, it might be as simple as only using the LLVM intrinsic on platforms where we know it works without library calls (not X86).

[dnadlinger]

So, actually, there is something you can do: Verify where the reference is and submit a patch. ;)

[mihails-strasuns]

Affirmative, will get to it soon-ish.

[mihails-strasuns]

Erm, but how can I find what generates reference to this specific symbol? Grepping for it in neither LDC sources nor LLVM headers finds anything.

# i686
[dicebot@microfog trunk]$ nm -D usr/lib/libldruntime-debug.so | grep __mulodi4
         U __mulodi4
[dicebot@microfog trunk]$ nm -D usr/lib/libldruntime.so | grep __mulodi4
         U __mulodi4
# x64_86
[dicebot@microfog trunk]$ nm -D usr/lib/libldruntime-debug.so.so | grep __mulodi4
# nothing

[mihails-strasuns]

reddit comment http://www.reddit.com/r/programming/comments/2pvf68/armv7_vs_x8664_pathfinding_benchmark_of_c_d_go/cn0hq95 , says they ship/link compiler-rt to address same issue in Rust

[dnadlinger]

Yes, this might also be an option. For the moment, the simple fix would be to just use the slow upstream implementations as core.checkedint isn't really used right now (as far as I know). We should definitely consider at least incorporating the relevant parts of compiler-rt in the future, though.

[mihails-strasuns]

Using this diff as a workaround seems to help : https://github.com/Dicebot/Arch-PKGBUILDs/blob/master/ldc/mul.diff

[mihails-strasuns]

Would you prefer to keep this issue open as a reminder for pending better solution or should I close it?

[dnadlinger]

Let's keep it open until we actually fix the issue in our tree. I'm working against a deadline right now, though, so I can't really spend any time on the necessary testing, however trivial it might be.