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

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Message-ID: <938b3544-535c-487c-92d3-6f544231b7f7@iogearbox.net>
Date: Mon, 20 Jan 2025 16:51:09 +0100
From: Daniel Borkmann <daniel@...earbox.net>
To: Jinghao Jia <jinghao7@...inois.edu>, Ruowen Qin <ruqin@...hat.com>,
 Alexei Starovoitov <ast@...nel.org>, 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>,
 Masahiro Yamada <masahiroy@...nel.org>, bentiss@...nel.org
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] samples/bpf: fix broken vmlinux path for VMLINUX_BTF



On 1/20/25 3:30 AM, Jinghao Jia 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)
>   VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))
>   
>   $(obj)/vmlinux.h: $(VMLINUX_BTF) $(BPFTOOL)

samples/hid/Makefile needs this fix as well :

VMLINUX_BTF_PATHS ?= $(abspath $(if $(O),$(O)/vmlinux))                         \
                      $(abspath $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)) \
                      $(abspath ./vmlinux)
VMLINUX_BTF ?= $(abspath $(firstword $(wildcard $(VMLINUX_BTF_PATHS))))