Linker Error when using rust-http in a dylib (plugin)

[reem]

Reproduce: https://github.com/reem/rust-http-content-type

The linker error goes away if you remove the implementation of this method: https://github.com/reem/rust-http-content-type/blob/master/generator/src/download.rs#L7-L24, which is the only usage of rust-http.

The actual error, I believe, has to do with rust-https usage of rust-openssl, but I don't really know how to debug any further.

Opening this issue because @huonw suggested it after we tried to debug.

Actual Error Log:

   Compiling generator v0.1.0 (https://github.com/reem/rust-http-content-type.git#6f656bbe)
error: linking with `cc` failed: exit code: 1
note: cc '-m64' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-o' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/libgenerator-e170cac01c08bdc6.dylib' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/generator-e170cac01c08bdc6.o' '-Wl,-force_load,/usr/local/lib/rustlib/x86_64-apple-darwin/lib/libmorestack.a' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/generator-e170cac01c08bdc6.metadata.o' '-nodefaultlibs' '-fno-lto' '-Wl,-dead_strip' '-L' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps' '-lphf_mac-78b8694be35c3487' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/libhttp-b27c1e7938f5a5d0.rlib' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/libopenssl-fbe75530f7eda428.rlib' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/liburl-921578b148f50e06.rlib' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps/libencoding-4805bc5305f7cd87.rlib' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lrustc-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lrbml-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lrustc_llvm-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lflate-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lgraphviz-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lgetopts-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lrustc_back-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lsyntax-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-larena-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-ldebug-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lfmt_macros-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lterm-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-ltime-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lserialize-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-llog-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lregex-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lstd-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lsync-4e7c5e5c' '-L' '/usr/local/lib/rustlib/x86_64-apple-darwin/lib' '-lrustrt-4e7c5e5c' '-L' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps' '-L' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/deps' '-L' '/Users/Jonathan/hackreactor/iron-middleware/cookie/target/native/http-b27c1e7938f5a5d0' '-L' '/Users/Jonathan/.cargo/git/checkouts/rust-http-content-type-e95bbac12cca2eca/master/generator/.rust' '-L' '/Users/Jonathan/.cargo/git/checkouts/rust-http-content-type-e95bbac12cca2eca/master/generator' '-lssl' '-lcrypto' '-lpthread' '-ledit' '-lm' '-lc++' '-lSystem' '-lpthread' '-lc' '-lm' '-dynamiclib' '-Wl,-dylib' '-lcompiler-rt'
note: ld: warning: directory not found for option '-L/Users/Jonathan/.cargo/git/checkouts/rust-http-content-type-e95bbac12cca2eca/master/generator/.rust'
Undefined symbols for architecture x86_64:
  "_BN_is_zero", referenced from:
      bn::BigNum.Zero::is_zero::h0dfd42cc0d9b593ebTa in libopenssl-fbe75530f7eda428.rlib(openssl-fbe75530f7eda428.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[alexcrichton]

This may be a dupe of #14344, but I'd want to investigate more thoroughly.

[alexcrichton]

Actually, this is a bug in rust-openssl

$ grep -R BN_is_zero /usr/include  
/usr/include/openssl/bn.h:#define BN_is_zero(a)       ((a)->top == 0)

Looks like the symbol is a macro, not an actual function on some platforms.

[alexcrichton]

cc @sfackler

[reem]

@alexcrichton Thanks a ton for figuring this out. I've was struggling to figure this out all day yesterday.

[reem]

Hmmm.. I tried to fix this with sfackler/rust-openssl#64 but the error hasn't changed. Any ideas?

[sfackler]

Are you sure you're pulling the new version?

[reem]

Yes.

[reem]

This is super strange because it only happens when you try to use it in a dylib (specifically a plugin) - using rust-openssl in something static works fine.

[emk]

Yup. This is still failing on my builds, too, which run cargo update.

[reem]

@alexcrichton Since there aren't any problems using rust-openssl as a static library or in a static library, I think this is potentially a rust issue instead of an openssl issue, especially with the latest fix for BN_is_zero being a macro.

[reem]

I'm especially convinced that this is an error because you can find bn_is_zero.o in target/native/open-ssl-hash/ in generator in rust-http-content-type and that definitely defines a bn_is_zero. Creating a .a instead of a .o does nothing to relieve the error.

[alexcrichton]

@reem, your comment here: sfackler/rust-openssl#64 (comment) is not quite true, you need to assemble the object file into an archive and then provide a #[link] directive for the compiler to pick up the library. This is likely why you're still seeing the symbol error.