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

[Ihor Solodrai]

On 5/14/26 2:32 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 accepts either a full path or "ld.lld-15" style inputs to
> -fuse-ld= so this will work with LLD defined the same way as the other
> LLVM tools. However, for full paths, we need to use ".../ld.lld" instead
> of the generic driver "lld", but I don't think the original use of "lld"
> was significant as this is always a linux build.
> 
> Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
> ---
>  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..44ba829e5d4d 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 := $(LLD)
>  else
> -LLD := $(shell command -v $(LD))
> +USE_LD := $(shell command -v $(LD))
>  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 \

Hi James,

This patch breaks the selftests/bpf build:

$ clang --version
clang version 22.1.3 (CentOS 22.1.3-1.el9)
Target: x86_64-redhat-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Configuration file: /etc/clang/x86_64-redhat-linux-gnu-clang.cfg

$ make LLVM=1 -j$(nproc)
  [...] # ok

$ make LLVM=1 -C tools/testing/selftests/bpf -j$(nproc)

[...] # somewhere in the middle

  LIB      liburandom_read.so
clang: error: invalid linker name in argument '-fuse-ld=ld.lld'
make: *** [Makefile:256: /home/isolodrai/workspace/review/linux/tools/testing/selftests/bpf/liburandom_read.so] Error 1
make: Leaving directory '/home/isolodrai/workspace/review/linux/tools/testing/selftests/bpf'

[...]

Or a simpler reproducer:

$ make LLVM=1 OUTPUT=/tmp/out /tmp/out/liburandom_read.so
  LIB      liburandom_read.so
clang: error: invalid linker name in argument '-fuse-ld=ld.lld'
make: *** [Makefile:256: /tmp/out/liburandom_read.so] Error 1

$ make LLVM=-22 OUTPUT=/tmp/out /tmp/out/liburandom_read.so
  LIB      liburandom_read.so
clang-22: error: invalid linker name in argument '-fuse-ld=ld.lld-22'
make: *** [Makefile:256: /tmp/out/liburandom_read.so] Error 1

I tried your patches, and only then noticed BPF CI caught this too:
https://github.com/kernel-patches/bpf/actions/runs/25943477658/job/76267174885?pr=12082

>  		     -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
>