Re: [PATCH bpf-next] selftests/bpf: define string const as global for test_sysctl_prog.c

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: bpf <bpf@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH bpf-next] selftests/bpf: define string const as global for test_sysctl_prog.c
Date: Thu, 10 Sep 2020 20:03:33 -0700	[thread overview]
Message-ID: <CAADnVQ+cFw-b5GsyeUpFeSLJinbg5kNyHexf0hrERdj1eWUzAw@mail.gmail.com> (raw)
In-Reply-To: <20200910202718.956042-1-yhs@fb.com>

On Thu, Sep 10, 2020 at 1:27 PM Yonghong Song <yhs@fb.com> wrote:
>
> When tweaking llvm optimizations, I found that selftest build failed
> with the following error:
>   libbpf: elf: skipping unrecognized data section(6) .rodata.str1.1
>   libbpf: prog 'sysctl_tcp_mem': bad map relo against '.L__const.is_tcp_mem.tcp_mem_name'
>           in section '.rodata.str1.1'
>   Error: failed to open BPF object file: Relocation failed
>   make: *** [/work/net-next/tools/testing/selftests/bpf/test_sysctl_prog.skel.h] Error 255
>   make: *** Deleting file `/work/net-next/tools/testing/selftests/bpf/test_sysctl_prog.skel.h'
>
> The local string constant "tcp_mem_name" is put into '.rodata.str1.1' section
> which libbpf cannot handle. Using untweaked upstream llvm, "tcp_mem_name"
> is completely inlined after loop unrolling.
>
> Commit 7fb5eefd7639 ("selftests/bpf: Fix test_sysctl_loop{1, 2}
> failure due to clang change") solved a similar problem by defining
> the string const as a global. Let us do the same here
> for test_sysctl_prog.c so it can weather future potential llvm changes.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>

Applied. Thanks