* Doing a bpf trace of an XDP bpf program using bpf_perf_event_output()
@ 2020-02-10 14:41 Eelco Chaudron
2020-02-17 13:48 ` Eelco Chaudron
0 siblings, 1 reply; 2+ messages in thread
From: Eelco Chaudron @ 2020-02-10 14:41 UTC (permalink / raw)
To: Xdp; +Cc: Alexei Starovoitov
I'm trying to send a packet capture to user space using
bpf_perf_event_output(). However, the verifier is not liking the context
I pass to it.
Code looks something like this (note this is an fentry bpf type trace):
static inline void trace_to_perf_buffer(struct xdp_buff *xdp)
{
...
...
bpf_perf_event_output(xdp, &capture_map, flags,
&metadata, sizeof(metadata));
}
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;
}
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
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Doing a bpf trace of an XDP bpf program using bpf_perf_event_output()
2020-02-10 14:41 Doing a bpf trace of an XDP bpf program using bpf_perf_event_output() Eelco Chaudron
@ 2020-02-17 13:48 ` Eelco Chaudron
0 siblings, 0 replies; 2+ messages in thread
From: Eelco Chaudron @ 2020-02-17 13:48 UTC (permalink / raw)
To: Xdp; +Cc: Alexei Starovoitov
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
^ permalink raw reply [flat|nested] 2+ messages in thread
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