Re: [PATCH v2 5/6] tools/build: selftests: Allow versioning LLVM lld

On 5/18/26 2:03 AM, James Clark wrote:
> Building with LLVM=... could result in a different version of lld being
> used than the main toolchain for liburandom_read.so because it's
> hardcoded to "lld" in this makefile.
> 
> Make it consistent with the rest of the LLVM toolchain by adding an LLD
> variable to Makefile.include. Keep the fallback for other architectures
> in tools/testing/selftests/bpf/Makefile as it seems like it's something
> specific to this make rule and shouldn't be global.
> 
> Clang only accepts either a full path to "/x/x/ld.lld" or "lld-15" style
> inputs to "-fuse-ld=", so the only way to make it work with both
> prefixed and postfixed paths is to always take the full path. Also I
> don't think the original use of "lld" over "ld.lld" was significant as
> this is always a linux build, so that can be changed to make it work in
> both cases.
> 
> Signed-off-by: James Clark <[email protected]>
> ---
>  tools/scripts/Makefile.include       | 2 ++
>  tools/testing/selftests/bpf/Makefile | 8 ++++----
>  2 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/tools/scripts/Makefile.include b/tools/scripts/Makefile.include
> index 380ad84ac51e..5c2d505cba62 100644
> --- a/tools/scripts/Makefile.include
> +++ b/tools/scripts/Makefile.include
> @@ -67,6 +67,7 @@ ifneq ($(LLVM),)
>    $(call allow-override,HOSTAR,$(LLVM_PREFIX)llvm-ar$(LLVM_SUFFIX))
>    $(call allow-override,LD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
>    $(call allow-override,HOSTLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
> +  $(call allow-override,LLD,$(LLVM_PREFIX)ld.lld$(LLVM_SUFFIX))
>    $(call allow-override,CXX,$(LLVM_PREFIX)clang++$(LLVM_SUFFIX))
>    $(call allow-override,STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
>    $(call allow-override,LLVM_STRIP,$(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX))
> @@ -91,6 +92,7 @@ else
>    # Some tools still require Clang, LLC and/or LLVM utils
>    $(call allow-override,CLANG,clang)
>    $(call allow-override,LLC,llc)
> +  $(call allow-override,LLD,ld.lld)
>    $(call allow-override,LLVM_CONFIG,llvm-config)
>    $(call allow-override,LLVM_OBJCOPY,llvm-objcopy)
>    $(call allow-override,LLVM_STRIP,llvm-strip)
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 6ef6872adbc3..836e783f0170 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -245,9 +245,9 @@ $(OUTPUT)/%:%.c
>  
>  # LLVM's ld.lld doesn't support all the architectures, so use it only on x86
>  ifeq ($(SRCARCH),$(filter $(SRCARCH),x86 riscv))
> -LLD := lld
> +USE_LD := $(shell command -v $(LLD))
>  else
> -LLD := $(shell command -v $(LD))
> +USE_LD := $(shell command -v $(LD))

Can confirm v2 fixes the v1 breakage I reported.

One nit on the empty USE_LD case the bot raised. It isn't actually a
build failure: if command -v finds nothing, USE_LD is empty and clang
gets a bare "-fuse-ld=".

Since it's unintentional, how about we just add a check to ensure the
linker was found?

Something like:

    $(Q)test -n "$(USE_LD)" || { \
        echo "$@: linker '$(LINKER)' not found - add it to PATH, or pass \
        LLVM=/path/ or LLD=/abs/ld.lld" >&2; exit 1; }


>  endif
>  
>  # Filter out -static for liburandom_read.so and its dependent targets so that static builds
> @@ -258,7 +258,7 @@ $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom
>  		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) \
>  		     $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
>  		     -Wno-unused-command-line-argument \
> -		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
> +		     -fuse-ld=$(USE_LD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>  		     -Wl,--version-script=liburandom_read.map \
>  		     -fPIC -shared -o $@
>  
> @@ -268,7 +268,7 @@ $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_r
>  		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
>  		     -Wno-unused-command-line-argument \
>  		     -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
> -		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
> +		     -fuse-ld=$(USE_LD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>  		     -Wl,-rpath=. -o $@
>  
>  $(OUTPUT)/sign-file: ../../../../scripts/sign-file.c
>