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

[Fangrui Song via cfe-dev]

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