On Thu, Sep 10, 2020 at 1:30 PM Yonghong Song <yhs@xxxxxx> 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@xxxxxx>
> ---
Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> tools/testing/selftests/bpf/progs/test_sysctl_prog.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
> index 50525235380e..5489823c83fc 100644
> --- a/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
> +++ b/tools/testing/selftests/bpf/progs/test_sysctl_prog.c
> @@ -19,11 +19,11 @@
> #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
> #endif
>
> +const char tcp_mem_name[] = "net/ipv4/tcp_mem";
nit: I'd prefer keeping an empty line between variables and functions
> static __always_inline int is_tcp_mem(struct bpf_sysctl *ctx)
> {
> - char tcp_mem_name[] = "net/ipv4/tcp_mem";
> unsigned char i;
> - char name[64];
> + char name[sizeof(tcp_mem_name)];
> int ret;
>
> memset(name, 0, sizeof(name));
> --
> 2.24.1
>
