[lttng-dev] Padding with Fs in babeltrace for a 32 bits field (ctf_integer_hex)

[Philippe Proulx]

On Wed, Oct 22, 2014 at 5:31 PM, Boisvert, Sebastien <boisvert at anl.gov> wrote:
>> ________________________________________
>> From: Philippe Proulx [eeppeliteloop at gmail.com]
>> Sent: Wednesday, October 22, 2014 4:03 PM
>> To: Boisvert, Sebastien
>> Cc: lttng-dev at lists.lttng.org
>> Subject: Re: [lttng-dev] Padding with Fs in babeltrace for a 32 bits field (ctf_integer_hex)
>> On Wed, Oct 22, 2014 at 4:34 PM, Boisvert, Sebastien <boisvert at anl.gov> wrote:
>> > I am using LTTng-UST (lttng 2.4.1-1.el6) and babeltrace (1.2.1-1.el6) on CentOS 6.5 (using EPEL).
>> >
>> > I have 2 hexadecimal fields:
>> >
>> >       ctf_integer_hex(int, script, actor->script->identifier)
>> >       ctf_integer_hex(int, action, message->action)
>> >
>> > One of them is printed with leading Fs (64 bits) while the other is fine (32 bits), but both should be 32 bits wide.
>> >
>> > [14:52:27.416502837] (+0.000005124) silverclaw.novalocal thorium_actor:receive_exit: { cpu_id = 6 }, { name = 1000452, script = 0xFFFFFFFFEB3B39FD, action = 0x7724, count = 41 }
>> >
>> > I expect "script = 0xEB3B39FD" and not script = 0xFFFFFFFFEB3B39FD since this is a int (sizeof(int) is 4).
>> The issue is on the Babeltrace's ctf-text format side. When printing an
>> integer with base 16 (ctf_integer_hex()):
>> formats/ctf-text/types/integer.c:111:
>>     case 16:
>>     {
>>         uint64_t v;
>>         if (!integer_declaration->signedness)
>>             v = integer_definition->value._unsigned;
>>         else
>>             v = (uint64_t) integer_definition->value._signed;
>>         fprintf(pos->fp, "0x%" PRIX64, v);
>>         break;
>>     }
>> When the integer is signed, it's casted to a 64-bit unsigned integer,
>> hence the visible sign extension (all those Fs) in your case since the
>> actual recorded value is -348440067 (if I'm still good at mental two's
>> complement conversions ;-)).
>> I believe this choice in Babeltrace is okay. It's always weird to
>> represent a signed integer in hex base. How would you print it?
>
> The script identifier is found here:
> [boisvert at bigmem biosal]$ grep 39fd genomics/* -R
> genomics/assembly/unitig/unitig_visitor.h:#define SCRIPT_UNITIG_VISITOR 0xeb3b39fd
>
> I would just print as it is: 0xeb3b39fd
>
> $ cat foo.c
>
> #include <stdio.h>
> #define SCRIPT_UNITIG_VISITOR 0xeb3b39fd
>
> int main(int argc, char **argv)
> {
>     int script;
>     script = SCRIPT_UNITIG_VISITOR;
>     printf("0x%x\n", script);
>
>     return 0;
> }
> $ gcc foo.c
> $ ./a.out
> 0xeb3b39fd

Good point. So the integer's size should be checked instead of using PRI*
conversion specifications systematically.

I created a bug report for this: <http://bugs.lttng.org/issues/848>.

Phil
>
>
>> -0x14C4C603? I guess this would work too and could eventually be a
>> format option passed to Babeltrace.
>> Hope it helps, somehow,
>> Phil
>> >
>> > Am I doing something wrong ?
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