[GHC] #13541: Make it easier to use the gold linker

[GHC]

#13541: Make it easier to use the gold linker
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by angerman):

 Replying to [comment:11 nh2]:
 > Replying to [comment:5 angerman]:
 > > I'm also a bit confused why gcc would not respect the LD env var.
 >
 > I guess this may be controversial, but I have always liked the fact that
 cabal and GHC rely as little as possible on environment variables.
 >
 > It has made it much easier many times for me to debug ghc issues
 (funnily, especially the linker investigation) because I can see all
 relevant inputs to a ghc invocation simply in `ps` or `strace`, and re-run
 them to isolate problems without accidentally not replicating the
 environment correctly.

 My personal issue with not respecting env variables is that, without
 respecting the environment, one has to

 - have explicit flags for each possible configuration value, that
 otherwise would have been taken from the environment.

 - by not using the environment, one is posed to break tooling that depends
 on the environment.

 GHC already has a lot of logic to find tools at configuration time and
 store their paths. `FIND_LD` already tries to detect gold, (and fails for
 the android toolchain...)

 I am much more in favor of doing tool checking rather than magic. What I
 mean is this: instead of trying hard to find some tool (say ld), use $LD.
 However if we know we want gold, try `$LD --version` to verify it actually
 *is* gold. And if it's not, put out a warning that $LD is not set to
 `gold` and that this is known not to work. However if you want to ignore
 the error pass `--compat-warning-only`. Which would then print a warning:

 > Warning: linker ($LD) does not seem to be gold. Continuing anyway due to
 --compat-warning-only.

 instead of

 > Error: linker ($LD) does not seem to be gold. bfd is known not to work.
 To continue anyway, pass --compat-warning-only.

 Then again, this makes me wonder why we test for gold, and not against bfd
 in the first place? Why force gold, if lld is fine as well, when all we
 want is to make sure we don't use a buggy/broken/slow linker called bfd?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13541#comment:14>
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