Gold fails to make a relocatable object file from a static library

Let me preface this by saying that I'm a noob in things related to linkers. If something I say seems like it makes no sense, it probably doesn't - please call me out on it.

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I've got the following files:

• bar.rs

  #[no_mangle]
  pub extern fn bar(x: isize) -> isize { x + 1 }
  

• foo.c

  extern int bar(int);
  extern int baz(int);
  int foo(int x) { return bar(x) + baz(x); }
  

I can link these into one relocatable object file with:

$ rustc --crate-type=staticlib bar.rs -o bar.a
$ gcc -c foo.c -o foo.o
$ ld -r foo.o bar.a -o out.o

I'm not sure what is happening under the hood, but I sure do get the output I wanted: bar and foo are defined while baz isn't.

$ nm out.o | grep '\(foo\|bar\|baz\)$'
0000000000000000 T bar
                 U baz
0000000000000000 T foo

Exactly the same thing happens if I replace ld with ld.bfd. However, things fall apart with ld.gold.

$ ld.gold -r foo.o bar.a -o out.o
ld.gold: internal error in set_info_section, at ../../gold/output.h:3198

This is with both ld.gold packaged with binutils 2.24 and 2.26.

The problem persists with binutils 2.30, although the line number I get is different:

$ ld.gold -r foo.o bar.a -o out.o
ld.gold: internal error in set_info_section, at ../../gold/output.h:3386

Also, the error persists even with --emit=obj instead of --crate-type=staticlib

So:

• What does the error mean?
• How can I achieve the same relocatable object output with ld.gold as with ld and ld.bfd?

Reported here. Turns out this is already fixed in trunk, so I guess the solution is to wait until binutils 2.31 (or build binutils from scratch).