RFA/RFC: Enable both gold and ld in a single toolchain

[Nick Clifton]

Hi Guys,

  I have created a patch (attached) that enables both GOLD and LD to be
  built and used in a single toolchain.  This allows easy comparison of
  the two linkers with just a single command line switch to choose
  between them.

  I suspect that the patch may not be approved, but I wanted to
  contribute it in case anyone else was interested in this facility.

  In order to build both linkers it is necessary to run the top level
  configure script with the switch:

    --enable-gold=both

  Then once the linkers are built/installed you can add:

    -Luse-gold

  to a gcc command line to use the GOLD linker.  Otherwise the LD linker
  (aka gld) will be used.

  There is one special caveat though.  When installing the two linkers
  it is necessary to install gold before ld as otherwise the ld linker
  will be overwritten.  Ie run:

    make ... install-gold install-ld ...


  The choice of -Luse-gold as the switch to select the gold linker is a
  hack.  One of the requirements for programs and scripts that sit
  between gcc and the linker, (such as collect2 and collect-ld), is that
  gcc must continue to work if they are not there and the linker is
  invoked directly.  Thus any options that are intended for the
  intermediate programs/scripts must be disguised in some fashion.
  
  Collect2 uses environment variables to get its options but this is,
  IMHO, heinous.  So instead I chose to use the -L switch.  This can
  take an arbitrary text argument and it will not cause the linker to
  complain if the argument is not recognised or the so called library
  search path does not actually exist.  In theory it could break a link
  if there really is a sub-directory of the current directory called
  "use-gold" and this directory contains subtly invalid binaries, but
  this is very unlikely to happen.

  Comments welcome, and if the gcc maintainers feel that this feature is
  actually wanted in the mainstream sources I will happy to apply my
  patch and maintain it in the future.

  Tested with i686-pc-linux-gnu, sparc-elf and arm-eabi toolchains, and
  an x86 bootstrap.  (That is bootstrapping without gold enabled, just
  to make sure that I did not break anything).

Cheers
  Nick

./ChangeLog
2010-03-04  Nick Clifton  <nickc@redhat.com>

	* configure.ac (--enable-gold): Accept a value of "both".  If
	this value is given then configure both ld and gold.
        * configure: Regenerate.

gcc/ChangeLog
2010-03-04  Nick Clifton  <nickc@redhat.com>

	* configure.ac (gcc_cv_gold_srcdir): New cached variable -
	contains the location of the gold sources.
        (ORIGINAL_GOLD_FOR_TARGET): New substituted variable - contains
	the name of the locally built gold executable.
        * configure: Regenerate.
        * collect2.c (main): Detect the -Luse-gold switch and select the
	gold linker, if found.
        * exec-tool.in: Detect the -Luse-gold switch and select the gold
	linker, if found.  Add support for -v switch.  Report problems
	locating linker executable.

gold/ChangeLog
2010-03-04  Nick Clifton  <nickc@redhat.com>

	* Makefile.am (install-exec-local): Also install the executable
	as a binary named 'gold'.
        * Makefile.in: Regenerate.

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