linux-kernel - Re: [PATCH bpf] samples/bpf: fix broken vmlinux path for VMLINUX

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Message-ID: <CAK7LNASn2aS6kcOy2Ur=tv_0fuEw8Gv06cVrOJ0x==AD9YRwRg@mail.gmail.com>
Date: Tue, 21 Jan 2025 09:42:48 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Jinghao Jia <jinghao7@...inois.edu>
Cc: Ruowen Qin <ruqin@...hat.com>, 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>, Nicolas Schier <n.schier@....de>, bpf@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] samples/bpf: fix broken vmlinux path for VMLINUX_BTF

On Mon, Jan 20, 2025 at 11:30 AM Jinghao Jia <jinghao7@...inois.edu> wrote:
>
> Commit 13b25489b6f8 ("kbuild: change working directory to external
> module directory with M=") changed kbuild working directory of bpf
> samples to $(srctree)/samples/bpf, which broke the vmlinux path for
> VMLINUX_BTF, as the Makefile assumes the current work directory to be
> $(srctree):
>
>   Makefile:316: *** Cannot find a vmlinux for VMLINUX_BTF at any of "  /path/to/linux/samples/bpf/vmlinux", build the kernel or set VMLINUX_BTF like "VMLINUX_BTF=/sys/kernel/btf/vmlinux" or VMLINUX_H variable.  Stop.
>
> Correctly refer to the kernel source directory using $(srctree).
>
> Fixes: 13b25489b6f8 ("kbuild: change working directory to external module directory with M=")
> Tested-by: Ruowen Qin <ruqin@...hat.com>
> Signed-off-by: Jinghao Jia <jinghao7@...inois.edu>
> ---
>  samples/bpf/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 96a05e70ace3..f97295724a14 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -307,7 +307,7 @@ $(obj)/$(TRACE_HELPERS): TPROGS_CFLAGS := $(TPROGS_CFLAGS) -D__must_check=
>
>  VMLINUX_BTF_PATHS ?= $(abspath $(if $(O),$(O)/vmlinux))                                \
>                      $(abspath $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)) \
> -                    $(abspath ./vmlinux)
> +                    $(abspath $(srctree)/vmlinux)

This is wrong and will not work for O= build.

The prefix should be $(objtree)/





>  VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
>
>  $(obj)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL)
> --
> 2.48.1
>


-- 
Best Regards
Masahiro Yamada