Trying to get GDB to find PE symbol file via build-id

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Hi all,

I'm trying to build a Win32 DLL with separate debug symbols, but I
can't seem to get GDB to automatically load a symbol file using the PE
build-id support added in ld 2.25.  I'm running on Fedora 21 x86_64,
with a gdb built from binutils-gdb HEAD (3e95021) and configured with
"--target=i686-w64-mingw32".

What I'm doing:

1.  Cross-build the DLL with MinGW-w64 and LDFLAGS="-Wl,--build-id".

2.  Create stripped DLL with "i686-w64-mingw32-objcopy -S
unstripped.dll stripped.dll".

3.  Create symbol file with "i686-w64-mingw32-objcopy
--only-keep-debug unstripped.dll debug/.build-id/MM/NNNN.debug", where
"MMNNNN" is the hex string returned by "i686-w64-mingw32-objdump -p
unstripped.dll | grep signature".

4.  In i686-w64-mingw32-gdb, run "set debug-file-directory debug" and
"file stripped.dll".

Result: "Reading symbols from stripped.dll...(no debugging symbols
found)...done."

An strace of the gdb process shows that it doesn't try to access any
.debug files in debug/, so the problem isn't that I used the wrong
filename.  Manually loading the symbol file with "symbol-file
debug/.build-id/MM/NNNN.debug" does work.

Advice?  Am I going about this wrong?

Thanks,
--Benjamin Gilbert