[lttng-dev] Printing bit fields with LTTng

[Simon Marchi]

On 10 June 2015 at 17:16, Chidhu R <chid1989 at gmail.com> wrote:
> Hello,
>
> I am getting compilation issues while trying to print bit field values with
> LTTng.
>
> Error:
>
> hello.c: In function ‘main’:
> hello.c:36:1: error: ‘typeof’ applied to a bit-field
> hello.c:36:1: error: ‘typeof’ applied to a bit-field
> hello.c:36:1: error: ‘typeof’ applied to a bit-field
> hello.c:36:1: error: ‘sizeof’ applied to a bit-field
>
> Snippet:
>
> struct abc{
>         int a:16;
>         int b:8;
> };
>
> Line 36: tracepoint(hello_world, my_third_tracepoint, aa.a, "welcome");
> Line 37: printf("val = %x\n",aa.a);
>
> tracepoint line results in compilation error.
> printf succeeds.
>
> Tp definition looks like this.
>
> TRACEPOINT_EVENT(
>     hello_world,
>     my_third_tracepoint,
>     TP_ARGS(
>         uint32_t, arg,
>         const char * , my_string_arg
>     ),
>     TP_FIELDS(
>         ctf_integer_hex(uint32_t, my_arg, arg)
>         ctf_string(field, my_string_arg)
>     )
> )
>
> How to print bit field values?
>
> Thanks
> Chid

I have no idea what the right fix would be, but an easy workaround
could be to add 0 to your value:

    tracepoint(hello_world, my_third_tracepoint, aa.a + 0, "welcome");

I just tried it and it works.

Simon