I created a test case on fc25 (kernel 4.8.6) like below and it works
fine for me.
unsigned char *data = (unsigned char *)(long)skb->data;
unsigned char *data_end = (unsigned char *)(long)skb->data_end;
if (data + 2 > data_end)
return 0;
char fmt[] = "%u\n";
bpf_trace_printk_(fmt, sizeof(fmt), *data);
On Fri, Jun 30, 2017 at 2:25 PM, MD I. Islam <tamim@xxxxxxxxxxx> wrote:
> I tried to cast it into int *. In that case, it should print the
> integer. But I get the same problem.
>
> On Fri, Jun 30, 2017 at 5:16 PM, Y Song <ys114321@xxxxxxxxx> wrote:
>> Maybe *data is not a printable character?
>>
>> On Fri, Jun 30, 2017 at 12:54 PM, MD I. Islam <tamim@xxxxxxxxxxx> wrote:
>>> Hi
>>>
>>> I have following code attached to an interface:
>>>
>>> SEC("simple")
>>> int handle_ingress(struct __sk_buff *skb)
>>> {
>>> unsigned char *data = (unsigned char *)(long)skb->data;
>>> char fmt[] = "%u\n";
>>> bpf_trace_printk(fmt, sizeof(fmt), *data);
>>> return 0;
>>> }
>>>
>>> When packets pass through the interface, it does not print anything at
>>> /sys/kernel/debug/tracing/trace_pipe. However if I do
>>> bpf_trace_printk(fmt, sizeof(fmt), data), it prints the pointer. Could
>>> you please advise what is wrong here?
>>>
>>> Many thanks
>>> Tamim
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