RFR: JDK-8217723 Switch ld from bfd to gold on gcc toolchain

[Florian Weimer]

* Martin Buchholz:

> Here's an experiment using the 3 competing open source linkers to link
> hotspot.  This confirms that lld is faster than gold is faster than
> bfd, but is the one second saving worth the engineering effort?
>
>  $ (BUILDDIR=$HOME/ws/jdk/build/linux-x86_64-server-release; for
> linker in bfd gold lld; do echo --- $linker ---; time /usr/bin/g++
> -fuse-ld=$linker -Wl,--hash-style=both -Wl,-z,defs -Wl,-z,noexecstack
> -Wl,-O1 -Wl,-z,relro -m64 -static-libstdc++ -static-libgcc -shared
> -m64 -Wl,-version-script=$BUILDDIR/hotspot/variant-server/libjvm/mapfile
> -Wl,-soname=libjvm.so -o
> $BUILDDIR/support/modules_libs/java.base/server/libjvm.so
> @$BUILDDIR/hotspot/variant-server/libjvm/objs/_BUILD_LIBJVM_objectfilenames.txt
> -lm -ldl -lpthread; done)
> --- bfd ---
> /usr/bin/g++ -fuse-ld=$linker -Wl,--hash-style=both -Wl,-z,defs
> -Wl,-O1  -m6  1.31s user 0.36s system 99% cpu 1.669 total
> --- gold ---
> /usr/bin/g++ -fuse-ld=$linker -Wl,--hash-style=both -Wl,-z,defs
> -Wl,-O1  -m6  0.42s user 0.11s system 99% cpu 0.537 total
> --- lld ---
> /usr/bin/g++ -fuse-ld=$linker -Wl,--hash-style=both -Wl,-z,defs
> -Wl,-O1  -m6  0.25s user 0.20s system 145% cpu 0.310 total

Do the constituent object files have debugging information?  Sub-second
processing times for ~350 MiB of output are rather impressive.

On a Sandybridge-era Xeon (probably without SSD storage), I see a change
from 13 seconds to 8 seconds (BFD to gold).  This is the first libjvm.so
link from “make images”, and the output includes (apparently full)
debugging information.

Thanks,
Florian