Re: [PATCH bpf-next 1/2] bpf: change var type of BTF_ID_LIST to static

From: Yonghong Song <yhs@fb.com>
To: kernel test robot <lkp@intel.com>, <bpf@vger.kernel.org>,
	<netdev@vger.kernel.org>
Cc: <kbuild-all@lists.01.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jiri Olsa <jolsa@kernel.org>, <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: change var type of BTF_ID_LIST to static
Date: Fri, 17 Jul 2020 22:10:55 -0700	[thread overview]
Message-ID: <b4c188bf-27f2-878d-88bf-7650f9b5904e@fb.com> (raw)
In-Reply-To: <202007180734.M4279SC8%lkp@intel.com>

On 7/17/20 4:12 PM, kernel test robot wrote:
> Hi Yonghong,
> 
> I love your patch! Yet something to improve:
> 
> [auto build test ERROR on bpf-next/master]
> 
> url:    https://github.com/0day-ci/linux/commits/Yonghong-Song/compute-bpf_skc_to_-helper-socket-btf-ids-at-build-time/20200718-025117
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
> config: x86_64-rhel-7.6-kselftests (attached as .config)
> compiler: gcc-9 (Debian 9.3.0-14) 9.3.0
> reproduce (this is a W=1 build):
>          # save the attached .config to linux build tree
>          make W=1 ARCH=x86_64
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@intel.com>
> 
> All error/warnings (new ones prefixed by >>):
> 
>     In file included from kernel/bpf/btf.c:21:
>>> kernel/bpf/btf.c:3625:13: warning: array 'bpf_ctx_convert_btf_id' assumed to have one element
>      3625 | BTF_ID_LIST(bpf_ctx_convert_btf_id)
>           |             ^~~~~~~~~~~~~~~~~~~~~~
>     include/linux/btf_ids.h:69:12: note: in definition of macro 'BTF_ID_LIST'
>        69 | static u32 name[];
>           |            ^~~~
>     /tmp/ccYr5IvF.s: Assembler messages:
>     /tmp/ccYr5IvF.s:23808: Error: symbol `bpf_ctx_convert_btf_id' is already defined

gcc8 is fine and gcc9 enforced the rules as `name` is defined both in 
assembly code and in C code. I guess `static u32 name[]` won't work.
I will restore to original `extern u32 name[]`.

Thanks.

> --
>     In file included from kernel/bpf/stackmap.c:12:
>>> kernel/bpf/stackmap.c:580:13: warning: array 'bpf_get_task_stack_btf_ids' assumed to have one element
>       580 | BTF_ID_LIST(bpf_get_task_stack_btf_ids)
>           |             ^~~~~~~~~~~~~~~~~~~~~~~~~~
>     include/linux/btf_ids.h:69:12: note: in definition of macro 'BTF_ID_LIST'
>        69 | static u32 name[];
>           |            ^~~~
>     /tmp/ccjqxVG0.s: Assembler messages:
[...]