linux-kernel - Re: [bpf-next] selftests/bpf: propagate LLVM toolchain into runqslower sub-make

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Message-ID: <CAEf4Bzbjbd-_3d2rpL1D72hngwNbSAbyPQDOn9fv0X4zpEcCCw@mail.gmail.com>
Date: Tue, 25 Nov 2025 14:43:20 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Hoyeon Lee <hoyeon.lee@...e.com>
Cc: bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev
Subject: Re: [bpf-next] selftests/bpf: propagate LLVM toolchain into
 runqslower sub-make

On Tue, Nov 18, 2025 at 8:38 PM Hoyeon Lee <hoyeon.lee@...e.com> wrote:
>
> The runqslower build invokes a nested make, but the selected LLVM

I think runqslower in kernel repo has long since served its purpose.
There is no point in maintaining its Makefile. The tool itself lives
in BCC repo. Its original purpose was to show real-world BPF-based
tooling end-to-end setup and implementation. BPF, libbpf, entire BPF
ecosystem has evolved and grown, I think we can remove runqslower now.
Do you mind just sending a patch dropping it instead?

pw-bot: cr


> toolchain (via LLVM=-<version>) is not propagated. This causes the
> sub-make to call the system-default 'clang' and 'llvm-strip' even when
> a specific LLVM version is intended.
>
>     # LLVM=-20 V=1 make -C tools/testing/selftests/bpf
>     ...
>     make -C tools/bpf/runqslower ...
>     clang -g -O2 --target=bpfel -I... -c runqslower.bpf.c -o runqslower.bpf.o && \
>           llvm-strip -g runqslower.bpf.o
>     /bin/sh: 1: clang: not found
>
>     (expected: clang-20 and llvm-strip-20)
>
> Propagate CLANG and LLVM_STRIP to the sub-make to ensure LLVM version
> consistency across all builds.
>
> Signed-off-by: Hoyeon Lee <hoyeon.lee@...e.com>
> ---
>  tools/testing/selftests/bpf/Makefile | 1 +
>  tools/testing/selftests/lib.mk       | 1 +
>  2 files changed, 2 insertions(+)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 34ea23c63bd5..79ab69920dca 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -306,6 +306,7 @@ endif
>
>  $(OUTPUT)/runqslower: $(BPFOBJ) | $(DEFAULT_BPFTOOL) $(RUNQSLOWER_OUTPUT)
>         $(Q)$(MAKE) $(submake_extras) -C $(TOOLSDIR)/bpf/runqslower            \
> +                   CLANG=$(CLANG) LLVM_STRIP=$(LLVM_STRIP)                    \
>                     OUTPUT=$(RUNQSLOWER_OUTPUT) VMLINUX_BTF=$(VMLINUX_BTF)     \
>                     BPFTOOL_OUTPUT=$(HOST_BUILD_DIR)/bpftool/                  \
>                     BPFOBJ_OUTPUT=$(BUILD_DIR)/libbpf/                         \
> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
> index a448fae57831..f14255b2afbd 100644
> --- a/tools/testing/selftests/lib.mk
> +++ b/tools/testing/selftests/lib.mk
> @@ -8,6 +8,7 @@ LLVM_SUFFIX := $(LLVM)
>  endif
>
>  CLANG := $(LLVM_PREFIX)clang$(LLVM_SUFFIX)
> +LLVM_STRIP := $(LLVM_PREFIX)llvm-strip$(LLVM_SUFFIX)
>
>  CLANG_TARGET_FLAGS_arm          := arm-linux-gnueabi
>  CLANG_TARGET_FLAGS_arm64        := aarch64-linux-gnu
> --
> 2.51.1
>
>