[cfe-dev] [RFC] Recognize -fuse-ld={bfd, gold, lld} but don't prepend "ld." or "ld64." for other values

[David Blaikie via cfe-dev]

The design then is to support composing -fuse-ld and -fld-path? So
things like -fuse-ld=gold
-fld-path=some-thing-like-gold-but-maybe-not-quite (if I want the
clang driver gold-specific behavior, but to use my custom linker
binary?)?

On Wed, Jul 1, 2020 at 5:54 PM Fangrui Song via cfe-dev
<cfe-dev at lists.llvm.org> wrote:
>
> On 2020-06-16, Fangrui Song wrote:
> >On 2020-06-03, Fangrui Song wrote:
> >>On 2020-06-03, David Chisnall via cfe-dev wrote:
> >>>On 02/06/2020 19:47, Fangrui Song via cfe-dev wrote:
> >>>>If they use a relative path, they can't be benefiting from ld. prefix
> >>>
> >>>This depends on how they specify the path.  If they specify a path
> >>>for the linker via -fuse-ld, they don't get the prefix.  Most
> >>>cross-compile toolchains that I've seen don't do that.  Instead,
> >>>they use -B to specify a path to find *all* of the tools and then
> >>>use -fuse-ld={lld,gold,bfd,proprietary linker's name}.
> >>>
> >>>That is the use case I'm concerned about breaking.  The behaviour
> >>>of -B is to prepend a search path, but still fall back to the
> >>>default paths if a tool is not found there.  For example, if I
> >>>have:
> >>>
> >>>/usr/bin/lld
> >>>/my/custom/sdk/bin/ld.lld
> >>>
> >>>If I run:
> >>>
> >>>$ clang -B /my/custom/sdk/bin/ -fuse-ld=lld ...
> >>>
> >>>Today, I will run my cross-compile toolchain's linker.  With your
> >>>proposed change, I will run my system LLD install.  As a user, I
> >>>will see very confusing error messages from the system linker if
> >>>it can't handle my cross-compile target.  Worse, I may see a
> >>>binary linked with a linker that defaults to a different linker
> >>>script, but still produces some output.
> >>>
> >>>David
> >>
> >>-fuse-ld={bfd,gold,lld} is compatible with the previous behavior.
> >>
> >>Do you propose that:
> >>
> >>* -fuse-ld={bfd,gold.lld} should find "ld.{bfd,gold,lld}" in COMPILER_PATH
> >>* all -fuse-ld=word should find "word" in COMPILER_PATH
> >>* -fuse-ld=relative/path should find "relative/path" in PATH?
> >
> >Thoughts?
>
> Created https://reviews.llvm.org/D83015 [Driver] Add -fld-path= and deprecate -fuse-ld=/abs/path and -fuse-ld=rel/path
>
> This should resolve jyknight's concern.
>
> I think GCC will be happy with whatever reasonable consensus we can reach:
> https://gcc.gnu.org/pipermail/gcc-patches/2020-July/549236.html
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