On Sat, Jul 1, 2017 at 1:08 PM, MD I. Islam <tamim@xxxxxxxxxxx> wrote:
> Thank you Song and Brenden! Apparently I do need to check the
> data_end. Is there a reason why it was silently ignoring the
> print_trace? I also got following warning;
>
> clang -nostdinc -isystem /usr/lib/gcc/x86_64-linux-gnu/5/include
> -I./arch/x86/include -I./arch/x86/include/generated/uapi
> -I./arch/x86/include/generated -I./include -I./arch/x86/include/uapi
> -I./include/uapi -I./include/generated/uapi -include
> ./include/linux/kconfig.h \
> -D__KERNEL__ -D__ASM_SYSREG_H -Wno-unused-value -Wno-pointer-sign \
> -Wno-compare-distinct-pointer-types \
> -Wno-gnu-variable-sized-type-not-at-end \
> -Wno-address-of-packed-member -Wno-tautological-compare \
> -O2 -emit-llvm -c samples/bpf/parse_simple.c -o -| llc -march=bpf
> -filetype=obj -o samples/bpf/parse_simple.o
> warning: unknown warning option '-Wno-address-of-packed-member'
> [-Wunknown-warning-option]
>
> Does it have anything to do with the problem?
No. This warning says that the option will be ignored. It should not
impact compilation.
>
> Many thanks
> Tamim
>
> On Sat, Jul 1, 2017 at 12:26 AM, Y Song <ys114321@xxxxxxxxx> wrote:
>> 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
|