On Wed, Apr 29, 2020 at 4:51 AM Eelco Chaudron <echaudro@xxxxxxxxxx> wrote:
>
> Hi Alexie at al.
>
> I was trying to attach a fentry/fexit trace to BPF_PROG_TYPE_EXT BPF
> program but I'm getting a verifier error, and not sure why. Is this
> supported?
The intent was to make it possible.
The verifier comment says:
/* Cannot fentry/fexit another fentry/fexit program.
* Cannot attach program extension to another extension.
* It's ok to attach fentry/fexit to extension program.
*/
> This is the error:
>
> libbpf: -- BEGIN DUMP LOG ---
> libbpf:
> arg#0 type is not a struct
> Unrecognized arg#0 type PTR
looks like verifier got confused here.
It should have detected correct btf_id from freplace prog.
not sure what's going on.
> ; int BPF_PROG(trace_on_entry, struct xdp_md *xdp)
> 0: (79) r1 = *(u64 *)(r1 +0)
> invalid bpf_context access off=0 size=8
> processed 1 insns (limit 1000000) max_states_per_insn 0 total_states 0
> peak_states 0 mark_read 0
> libbpf: -- END LOG --
>
> This is the actual fentry code using the BPF_PROG macro from
> tools/lib/bpf/bpf_tracing.h:
>
> SEC("fentry/func")
> int BPF_PROG(trace_on_entry, struct xdp_md *xdp)
> {
> trace_to_perf_buffer(xdp, false, 0);
> return 0;
> }
>
> And some more details from bpftool on the program I try to attach to:
>
> # bpftool prog show id 165
> 165: ext name xdp_test_I tag b5a46c6e9935298c gpl
> loaded_at 2020-04-28T13:41:00+0000 uid 0
> xlated 136B jited 108B memlock 4096B
> btf_id 432
>
> # bpftool prog dump xlated id 165
> int xdp_test_I(struct xdp_md * ctx):
> ; int xdp_test_I(struct xdp_md *ctx)
> 0: (b7) r2 = 10
> ; bpf_debug("PASS[1]: prog %u\n", ctx->ingress_ifindex);
> 1: (6b) *(u16 *)(r10 -8) = r2
> 2: (18) r2 = 0x752520676f727020
> 4: (7b) *(u64 *)(r10 -16) = r2
> 5: (18) r2 = 0x3a5d315b53534150
> 7: (7b) *(u64 *)(r10 -24) = r2
> 8: (79) r3 = *(u64 *)(r1 +40)
> 9: (79) r3 = *(u64 *)(r3 +0)
> 10: (61) r3 = *(u32 *)(r3 +256)
> 11: (bf) r1 = r10
> ;
> 12: (07) r1 += -24
> ; bpf_debug("PASS[1]: prog %u\n", ctx->ingress_ifindex);
> 13: (b7) r2 = 18
> 14: (85) call bpf_trace_printk#-54752
> ; return XDP_PASS;
> 15: (b7) r0 = 2
> 16: (95) exit
>
> Thanks in advance...
>
> //Eelco
>
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