ld if ${LD} != "ld"
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Authored by arichardson on Aug 13 2020, 2:09 PM.

Details

Reviewers

emaste
brooks
bdrewery
imp
jhb

Commits

rS364761: Pass -fuse-ld=/path/to/ld if ${LD} != "ld"

Summary

This is needed so that setting LD/XLD is not ignored when linking with $CC
instead of directly using $LD. Currently only clang accepts an absolute
path for -fuse-ld= (Clang 12+ will add a new --ld-path flag), so we now
warn when building with GCC and $LD != "ld" since that might result in the
wrong linker being used.

We have been XLD=/path/to/cheri/ld.lld in CheriBSD for a long time and
used a similar version of this patch to avoid linking with /usr/bin/ld.
This change is also required when building FreeBSD on an Ubuntu with Clang:
In that case we set XCC=/usr/lib/llvm-10/bin/clang and since
/usr/lib/llvm-10/bin/ does not contain a "ld" binary the build fails with
clang: error: unable to execute command: Executable "ld" doesn't exist!
unless we pass -fuse-ld=/usr/lib/llvm-10/bin/ld.lld.

Test Plan

buildworld+buildkernel failed on Ubuntu without this patch, now succeeds.

Diff Detail

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Build Status

Buildable 32971
Build 30363: arc lint + arc unit

Event Timeline

arichardson requested review of this revision.Aug 13 2020, 2:09 PM

arichardson created this revision.

Harbormaster completed remote builds in B32971: Diff 75781.Aug 13 2020, 2:09 PM

arichardson added a child revision: D16767: Add a tools/build/make.py script that bootstraps bmake and then runs the build.Aug 13 2020, 2:11 PM

arichardson mentioned this in D16767: Add a tools/build/make.py script that bootstraps bmake and then runs the build.Aug 13 2020, 2:19 PM

brooks accepted this revision.Aug 13 2020, 10:32 PM

This revision is now accepted and ready to land.Aug 13 2020, 10:32 PM

I'm fine with this change, although I wonder if we could/should start installing a (cross-)ld in our tools dir?

In D26055#578395, @emaste wrote:

I'm fine with this change, although I wonder if we could/should start installing a (cross-)ld in our tools dir?

Shouldn't it already contain a ld -> ld.lld symlink by default?

Shouldn't it already contain a ld -> ld.lld symlink by default?

Does the build work if we just pass a -B argument instead then?

In D26055#581284, @emaste wrote:

Shouldn't it already contain a ld -> ld.lld symlink by default?

Does the build work if we just pass a -B argument instead then?

It won't work on Ubuntu unless we pass -B <COMPILER_DIR> -fuse-ld=$(basename $XLD) since clang defaults to executing plain ld. Passing the full value of ${XLD} seems less fragile to me.

I guess we could also add ${XLD} to WOLRDTMP/bin/ld but then we have to ensure that this file does not exist while building the bootstrap tools since the cross-linker might not be compatible with the host linker (e.g. when building on macos: host-linker= Mach-O /usr/bin/ld, cross-linker=LLVM ld.lld).