netdev - Re: [PATCH bpf-next 0/2] bpf: support proper non-jit func info

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Date:   Mon, 26 Nov 2018 18:04:51 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH bpf-next 0/2] bpf: support proper non-jit func info

On Sat, Nov 24, 2018 at 11:20:43PM -0800, Yonghong Song wrote:
> Commit 838e96904ff3 ("bpf: Introduce bpf_func_info")
> added bpf func info support. The userspace is able
> to get better ksym's for bpf programs with jit, and
> is able to print out func prototypes.
> 
> For a program containing func-to-func calls, the existing
> implementation returns user specified number of function
> calls and BTF types if jit is enabled. If the jit is not
> enabled, it only returns the type for the main function.
> 
> This is undesirable. Interpreter may still be used
> and we should keep feature identical regardless of
> whether jit is enabled or not.
> This patch fixed this discrepancy.
> 
> The following example shows bpftool output for
> the bpf program in selftests test_btf_haskv.o when jit
> is disabled:
>   $ bpftool prog dump xlated id 1490
>   int _dummy_tracepoint(struct dummy_tracepoint_args * arg):
>      0: (85) call pc+2#__bpf_prog_run_args32
>      1: (b7) r0 = 0
>      2: (95) exit
>   int test_long_fname_1(struct dummy_tracepoint_args * arg):
>      3: (85) call pc+1#__bpf_prog_run_args32
>      4: (95) exit
>   int test_long_fname_2(struct dummy_tracepoint_args * arg):
>      5: (b7) r2 = 0
>      6: (63) *(u32 *)(r10 -4) = r2
>      7: (79) r1 = *(u64 *)(r1 +8)
>      8: (15) if r1 == 0x0 goto pc+9
>      9: (bf) r2 = r10
>     10: (07) r2 += -4
>     11: (18) r1 = map[id:1173]
>     13: (85) call bpf_map_lookup_elem#77088
>     14: (15) if r0 == 0x0 goto pc+3
>     15: (61) r1 = *(u32 *)(r0 +4)
>     16: (07) r1 += 1
>     17: (63) *(u32 *)(r0 +4) = r1
>     18: (95) exit
>   $ bpftool prog dump jited id 1490
>     no instructions returned

Applied to bpf-next. Thanks