Make dependency on lld optional during runtime build

[sbomer]

From @am11 in #84794 (comment):

• we can no longer build runtime repo with binutils alone.

i.e. LinkerFlavor=lld if target==linux constructs added are missing and Compiler!=gcc condition; we set Compiler at the start of build:

runtime/eng/build.sh

Line 432 in ed0f1c5

arguments="$arguments /p:Compiler=$compiler /p:CppCompilerAndLinker=$compiler"

(maps to ./build.sh -gcc)

The ability to compile with gcc+binutils is tested by the gcc product build leg, but this doesn't cover test builds. Conditions similar to

runtime/src/coreclr/tools/aot/ILCompiler/ILCompiler.csproj

Line 53 in dbd4233

<UseLLVMLinker Condition="'$(CppCompilerAndLinker)' == 'clang' and '$(TargetOS)' == 'linux'">true</UseLLVMLinker>

need to be added to nativeaot test builds. I believe this would cover building with gcc+binutils.

That still leaves the scenario of building with clang+bfd (where clang and binutils are installed, but lld isn't). From #84794 (comment):

changes in #84148 will "force" fuse-ld=lld unconditionally, disregarding #2's introspection based linker selection, and fail the build because we didn't install lld-16

When using clang as the linker driver, the NativeAot targets either explicitly use bfd (the default), or can be made to use lld via LinkerFlavor. So the fix for this would be to perform detection of lld when using the clang compiler, and set LinkerFlavor based on the result.

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Issue Details

---

From @am11 in #84794 (comment):

• we can no longer build runtime repo with binutils alone.

i.e. LinkerFlavor=lld if target==linux constructs added are missing and Compiler!=gcc condition; we set Compiler at the start of build:

runtime/eng/build.sh

Line 432 in ed0f1c5

arguments="$arguments /p:Compiler=$compiler /p:CppCompilerAndLinker=$compiler"

(maps to ./build.sh -gcc)

The ability to compile with gcc+binutils is tested by the gcc product build leg, but this doesn't cover test builds. Conditions similar to

runtime/src/coreclr/tools/aot/ILCompiler/ILCompiler.csproj

Line 53 in dbd4233

<UseLLVMLinker Condition="'$(CppCompilerAndLinker)' == 'clang' and '$(TargetOS)' == 'linux'">true</UseLLVMLinker>

need to be added to nativeaot test builds. I believe this would cover building with gcc+binutils.

That still leaves the scenario of building with clang+bfd (where clang and binutils are installed, but lld isn't). From #84794 (comment):

changes in #84148 will "force" fuse-ld=lld unconditionally, disregarding #2's introspection based linker selection, and fail the build because we didn't install lld-16

When using clang as the linker driver, the NativeAot targets either explicitly use bfd (the default), or can be made to use lld via LinkerFlavor. So the fix for this would be to perform detection of lld when using the clang compiler, and set LinkerFlavor based on the result.

Author:	sbomer
Assignees:	sbomer
Labels:	area-Infrastructure-coreclr, untriaged
Milestone:	-

[agocke]

This should also be checked by runtime-dev-innerloop. Do we run in a container that has lld in that case?

[sbomer]

It currently runs in the mariner images, but I think we should move it to something more representative - maybe Ubuntu 20.04 without lld.

[agocke]

I would suggest 22.04 (latest LTS), but yeah, agreed.