`binary_closure` failing to find `main` when linking about clodl HOT 11 CLOSED

Hello. The haskell_binary call is not passing "-pie" to ghc. The BUILD file shows how to do it, but not the example in the readme. I will mention it in the readme.

from clodl.

https://github.com/tweag/clodl#usage talks about the PIE requirement, but the binary_closure section should be made consistent with this later section.

from clodl.

Hi both. Thanks very much for responding to this. So I've added -pie (and -dynamic and -threaded, though those too appear to already be in the generated command line) to both my haskell_binary and, when that failed, to the haskell_library it depends on, to no avail. I then set about seeing if perhaps I needed to play the bootstrap trick you are playing in this repository (in which you export a cc_library of GHC's RTS includes and make main a weak symbol), but before I did so thought I'd check in here to see whether or not that's an expected requirement.

from clodl.

The bootstrap bit shoudn't be necessary. At least bazel run clotestbin doesn't use it and works in CI.

If you have a repo to share (or a gist or whatever), I could have a look.

from clodl.

I've created https://github.com/lunaris/bazel-example, which I think is a reproduction of the issue I'm seeing. It depends on a few common Haskell libraries to make sure there are a variety of cbits etc. floating around -- you can try and build a closure using bazel build //engine:test-closure. Many thanks!

from clodl.

Adding -rdynamic to compiler_flags fixes it for me. But I don't understand yet why it isn't necessary in the clodl repo.

from clodl.

Interesting. Is it perhaps that your bootstrapping stuff references main in a way that means it is considered a "used" symbol whereas in my example that recognition is missing for some reason?

from clodl.

That would explain it for the cases where we use the bootstrap library. But it also works without it.

from clodl.

That would explain it for the cases where we use the bootstrap library. But it also works without it.

I was wrong. Linking bootstrap does have an effect here, and we are always linking bootstrap.

Linking bootstrap into hello-hs includes main in the table of dynamic symbols:

$ nm -D bazel-bin/hello-hs | grep main
                 U hs_main
                 U __libc_start_main
00000000000024d3 T main

But if we don't link bootstrap, main is missing.

$ nm -D bazel-bin/engine/test-bin | grep main
                 U hs_main
                 U __libc_start_main

We will have to update the documentation to account for this. We either ask -rdynamic, or -Wl,--dynamic-list=<file with a list of symbols including main>. Also, we can test if the input binary defines main when using binary_closure and suggest in the error message one of these alternatives.

from clodl.

Thanks so much for helping out with this!

from clodl.

You're welcome. Thanks for reporting the issue and putting the testing repo together.

from clodl.