gold --incremental not producing DWARF such that nm can handle it, internal error

[Cary Coutant]

> * --incremental gold produces binaries st nm --line-numbers complains like this:
>
>      $ nm --line-numbers instrument_test >/dev/null
>      nm: Dwarf Error: Bad abbrev number: 0.
>      nm: Dwarf Error: found dwarf version '0', this reader only
> handles version 2, 3 and 4 information.
>      nm: Dwarf Error: found dwarf version '0', this reader only
> handles version 2, 3 and 4 information.
>
>   nm still coughs up the requested information but these are pretty
> disturbing warnings.

Gold adds padding to most sections during the first (full) incremental
link. For .debug_info sections, it makes the padding look like an
empty compilation unit, but other sections just get padded with
zeroes. I believe nm here is trying to read the .debug_line section,
assuming that it consists of one compilation unit after another. The
padding is at the end, so it's already found what it needs to by the
time it prints those messages. To work with incremental linking, nm
(and addr2line) will probably have to start with the .debug_info
section, which has pointers to each compilation unit's line number
table.

>        /home/bkerin/opt/binutils-2.26/bin/ld.gold: internal error in
> init_got_plt_for_update, at target.h:1023
>        collect2: error: ld returned 1 exit status
>        make: *** [instrument_test] Error 1
>        2 $
>
> Looking at gold/target.h:1023 it says something about a target needing
> to imlement a virtual function to support incremental linking, so
> maybe I didn't compile something right?  I just built
> binutils with ./configure --enable-gold=yes, perhaps something more is
> required to support incremental linking?

You didn't say what target you're building for, but --incremental
currently only works on x86_64. Sorry, there should be a better error
message. (I meant to add a target hook to claim support for
incremental linking, but kind of forgot.)

If you're building for x86_64, please post details on the binutils mailing list.

-cary