Re: Doing a bpf trace of an XDP bpf program using bpf_perf_event_output()

"Eelco Chaudron" <echaudro@xxxxxxxxxx> · Mon, 17 Feb 2020 14:48:27 +0100

On 10 Feb 2020, at 15:41, Eelco Chaudron wrote:

<SNIP<

SEC("fentry/xdpfilt_blk_all")
int BPF_PROG(trace_on_entry, struct xdp_buff *xdp)
{
    trace_to_perf_buffer(xdp);
    bpf_debug("fentry: [ifindex = %u, queue =  %u]\n",
          xdp->rxq->dev->ifindex, xdp->rxq->queue_index);
    return 0;
}

Ignore this email, as I totally missed the ctx hidden in the BPF_PROG() 

macro :(

The verifier does not like the context I pass:

...

from 9 to 13: R1=ptr_xdp_buff(id=0,off=0,imm=0) R2=inv(id=0) 

R3=inv(id=0) R4=ptr_xdp_buff(id=0,off=8,imm=0) R10=fp0

; metadata.pkt_len = (__u16)(data_end - data);
13: (1f) r2 -= r3
...
...
; bpf_perf_event_output((void *)xdp, &capture_map, flags,
42: (18) r2 = 0xffff9a55f047c000
44: (b7) r5 = 12
45: (85) call bpf_perf_event_output#25
R1 type=ptr_ expected=ctx

What context should I pass, or do I even have it in the bpf trace 

program?

Thanks,

Eelco