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

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Message-ID: <2e2d05b3-871b-42f3-8d66-d92653f01a72@illinois.edu>
Date: Tue, 21 Jan 2025 02:53:05 -0600
From: Jinghao Jia <jinghao7@...inois.edu>
To: Daniel Borkmann <daniel@...earbox.net>, 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 5:59 PM, Jinghao Jia wrote:
> 
> 
> On 1/20/25 9:51 AM, Daniel Borkmann wrote:
>>
>>
>> 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))))
>>
> 
> Oh yes you are right. I will roll out a v2.
> 
> --Jinghao
> 

The samples/hid Makefile also has the same problem that was fixed by
5a6ea7022ff4 ("samples/bpf: Remove unnecessary -I flags from libbpf
EXTRA_CFLAGS") for samples/bpf. I will include a fix for this in v2 as well.

--Jinghao