netdev - Re: [PATCH bpf-next] selftests/bpf: fix test_sysctl

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Date:   Tue, 8 Sep 2020 21:04:43 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: Re: [PATCH bpf-next] selftests/bpf: fix test_sysctl_loop{1,2} failure
 due to clang change

On Tue, Sep 8, 2020 at 8:12 PM Yonghong Song <yhs@...com> wrote:
> diff --git a/tools/testing/selftests/bpf/progs/test_sysctl_loop2.c b/tools/testing/selftests/bpf/progs/test_sysctl_loop2.c
> index b2e6f9b0894d..3c292c087395 100644
> --- a/tools/testing/selftests/bpf/progs/test_sysctl_loop2.c
> +++ b/tools/testing/selftests/bpf/progs/test_sysctl_loop2.c
> @@ -18,9 +18,9 @@
>  #define MAX_ULONG_STR_LEN 7
>  #define MAX_VALUE_STR_LEN (TCP_MEM_LOOPS * MAX_ULONG_STR_LEN)
>
> +const char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string_to_stress_byte_loop";
>  static __attribute__((noinline)) int is_tcp_mem(struct bpf_sysctl *ctx)
>  {
> -       volatile char tcp_mem_name[] = "net/ipv4/tcp_mem/very_very_very_very_long_pointless_string_to_stress_byte_loop";

It fixes the issue with new llvm, but breaks slightly older llvm:
 ./test_progs -n 7/21
libbpf: load bpf program failed: Permission denied
libbpf: -- BEGIN DUMP LOG ---
libbpf:
invalid stack off=0 size=1
verification time 6975 usec
stack depth 160+64
processed 889 insns (limit 1000000) max_states_per_insn 4 total_states
14 peak_states 14 mark_read 10

libbpf: -- END LOG --
libbpf: failed to load program 'sysctl_tcp_mem'
libbpf: failed to load object 'test_sysctl_loop2.o'
test_bpf_verif_scale:FAIL:114
#7/21 test_sysctl_loop2.o:FAIL

clang --version
clang version 12.0.0 (https://github.com/llvm/llvm-project.git
6f3511a01a5227358a334803c264cfce4175ca5d)