Re: [PATCH v3 bpf-next 17/18] selftests/bpf: Extend test_pkt_access test

[Song Liu <songliubraving@fb.com>]

> On Nov 7, 2019, at 10:40 PM, Alexei Starovoitov <ast@kernel.org> wrote:
> 
> The test_pkt_access.o is used by multiple tests. Fix its section name so that
> program type can be automatically detected by libbpf and make it call other
> subprograms with skb argument.
> 
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Acked-by: Song Liu <songliubraving@fb.com>

> ---
> .../selftests/bpf/progs/test_pkt_access.c     | 38 ++++++++++++++++++-
> 1 file changed, 36 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/progs/test_pkt_access.c b/tools/testing/selftests/bpf/progs/test_pkt_access.c
> index 7cf42d14103f..3a7b4b607ed3 100644
> --- a/tools/testing/selftests/bpf/progs/test_pkt_access.c
> +++ b/tools/testing/selftests/bpf/progs/test_pkt_access.c
> @@ -17,8 +17,38 @@
> #define barrier() __asm__ __volatile__("": : :"memory")
> int _version SEC("version") = 1;
> 
> -SEC("test1")
> -int process(struct __sk_buff *skb)
> +/* llvm will optimize both subprograms into exactly the same BPF assembly
> + *
> + * Disassembly of section .text:
> + *
> + * 0000000000000000 test_pkt_access_subprog1:
> + * ; 	return skb->len * 2;
> + *        0:	61 10 00 00 00 00 00 00	r0 = *(u32 *)(r1 + 0)
> + *        1:	64 00 00 00 01 00 00 00	w0 <<= 1
> + *        2:	95 00 00 00 00 00 00 00	exit
> + *
> + * 0000000000000018 test_pkt_access_subprog2:
> + * ; 	return skb->len * val;
> + *        3:	61 10 00 00 00 00 00 00	r0 = *(u32 *)(r1 + 0)
> + *        4:	64 00 00 00 01 00 00 00	w0 <<= 1
> + *        5:	95 00 00 00 00 00 00 00	exit
> + *
> + * Which makes it an interesting test for BTF-enabled verifier.

This is interesting!