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

[H.J. Lu]

On Thu, Mar 4, 2010 at 11:21 AM, Nick Clifton <nickc@redhat.com> wrote:
> 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.
>
>

Here is another approach to enable both ld and gold:

http://sourceware.org/ml/binutils/2010-01/msg00275.html

It will install both linkers, as ld.bfd and ld.gold, and allow to choose
either ld.bfd or ld.gold as the default linker. Is that possible to
combine your approach with mine?

Thanks.


-- 
H.J.