We're also seeing lld+icecc issues here in Vewd. Originally it looked like a build-time protoc crash -- protoc compiled during the build for the host and linked with lld would die with a "protoc returned -8". Looks like the same underlying issue.

Can you also paste the commands you ran to compile and link?

Attaching the unzipped from from that tar.

Deleted: icecc_test 25.9 KB

icecc_test 25.9 KB View Download

Deleted: main.cc 83 bytes

main.cc 83 bytes View Download

Deleted: main.o 4.8 KB

main.o 4.8 KB Download

Looking at that object file, it appears to contain a section named .ctors, which is an older mechanism for calling constructors at startup time (the new mechanism uses a section named .init_array). On Linux, Clang will use .ctors by default if it detects a GCC installation older than 4.7.0 [1]. I guess it's possible that you have an old GCC installation on your build slaves.

I thought that lld had support for .ctors, but it may be buggy (which is probably something that we should fix). For the moment, you can work around the issue by passing -fuse-init-array to the compiler, which should force it to use .init_array.

[1] http://llvm-cs.pcc.me.uk/tools/clang/lib/Driver/ToolChains/Gnu.cpp#2360

Thanks Peter for taking a look. I think I had a WIP patch to support .ctor, and it needs to be landed before the next major release.

In the meantime, could lld error out on .ctor with some "error: not yet implemented" instead of silently doing the wrong thing?

It may worth doing. (It should warn when we see both .ctors/.dtors and .init/fini, as I believe lld works fine if we do not mix the two.)

icecc runs the compiler in a chroot with very little inside, so maybe nothing at all gets detected as a candidate gcc

The question is what method Generic_GCC::GCCVersion::isOlderThan returns when there is no gcc detected. If it returns true (and probably it should) it explains why older mechanism is used.

Isn't there a compiler flag to force .init/.fini?

Maybe the compiler should default to .init/.fini if no gcc installation can be detected?

Yes, -fuse-init-array

Nico, I think that's a reasonable change. .ctors/.dtors are pretty old and mostly obsolete, and if clang is the only compiler installed to a system, it implies that the system is really new.

So, plan:
1. Make clang use .init/.fini if no gcc detected (pcc, want to do this, or should I?)
2. Make lld error on mixed .ctors/.init instead of silently mislinking (ruiu?)
3. (At some point in the future) .ctors support in lld

?

The clang change makes sense to me. Nico, could you take care of it, please?

https://reviews.llvm.org/D39317 for 1

I can confirm that -fuse-init-array fixes the protoc crash when icecc and lld are used.

-fuse-init-array fixes problem with example attached to the bug.

comment 17 landed in llvm r316713, this will be better after the next clang roll.

ruiu, are you adding the error message to lld or do you think it might not be necessary?

I am actually trying to finish up my patch to convert .ctors/dtors to .init/fini.

Let's call this fixed. I don't know if the ctors/dtors part is landed yet, but since clang no longer defaults to ctors/dtors this bug has been fixed for a while.