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?
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
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