dtrace discuss - Sep 2007 - Question about ''long long'' and USDT probes

Hello,

Someone provided me with an example of USDT usage that doesn''t appear
to work
right.  Namely, ''long long'' arguments get truncated when read
into the DTrace
script.

Here is a quick example and the output:

 > cat probetest.c
#include <stdio.h>
#include <sys/time.h>
#include <sys/sdt.h>

int main() {
   long long v = 0x0FFFFFFF00000001LL;

   printf("In the user process value = %llx\n",v);
   DTRACE_PROBE1(testprov,getvalue,v);
   return 0;
}

 > cc -c probetest.c
 > cat testprov.d
provider testprov {
         probe getvalue(long long);
};

#pragma D attributes Evolving/Evolving/Common provider testprov provider
#pragma D attributes Private/Private/Unknown provider testprov module
#pragma D attributes Private/Private/Unknown provider testprov function
#pragma D attributes Evolving/Evolving/Common provider testprov name
#pragma D attributes Evolving/Evolving/Common provider testprov args
 > dtrace -G -32 -s testprov.d probetest.o
 > cc -o probetest testprov.o probetest.o
 > cat test.d
testprov$target:::getvalue
{
         printf("In the D script value = %llx\n",arg0);
}
 > dtrace -s test.d -c ./probetest
dtrace: script ''test.d'' matched 1 probe
In the user process value = fffffff00000001
dtrace: pid 22849 has exited
CPU     ID                    FUNCTION:NAME
  20  46997                    main:getvalue In the D script value = 1


Anyone have any idea what I''m doing wrong here (if anything)?

--
- Keith

Hi Keith,

If you look at the definitions for the DTRACE_PROBE*() macros, you''ll
see
that the expected arguments are of type unsigned long. I''m surprised
your
compiler isn''t flagging that error.

If you use the newer USDT methodology, the generated header file will include
the appropriate types in the probe prototypes.

  http://blogs.sun.com/ahl/entry/user_land_tracing_gets_better

You may encounter the (long-standing) issue where 64-bit arguments on 32-bit
ISAs are split between two D arguments.

Adam

On Mon, Sep 10, 2007 at 02:31:43PM -0400, Keith McGuigan
wrote:
> Hello,
> 
> Someone provided me with an example of USDT usage that doesn''t
appear to work
> right.  Namely, ''long long'' arguments get truncated when
read into the DTrace
> script.
> 
> Here is a quick example and the output:
> 
>  > cat probetest.c
> #include <stdio.h>
> #include <sys/time.h>
> #include <sys/sdt.h>
> 
> int main() {
>    long long v = 0x0FFFFFFF00000001LL;
> 
>    printf("In the user process value = %llx\n",v);
>    DTRACE_PROBE1(testprov,getvalue,v);
>    return 0;
> }
> 
>  > cc -c probetest.c
>  > cat testprov.d
> provider testprov {
>          probe getvalue(long long);
> };
> 
> #pragma D attributes Evolving/Evolving/Common provider testprov provider
> #pragma D attributes Private/Private/Unknown provider testprov module
> #pragma D attributes Private/Private/Unknown provider testprov function
> #pragma D attributes Evolving/Evolving/Common provider testprov name
> #pragma D attributes Evolving/Evolving/Common provider testprov args
>  > dtrace -G -32 -s testprov.d probetest.o
>  > cc -o probetest testprov.o probetest.o
>  > cat test.d
> testprov$target:::getvalue
> {
>          printf("In the D script value = %llx\n",arg0);
> }
>  > dtrace -s test.d -c ./probetest
> dtrace: script ''test.d'' matched 1 probe
> In the user process value = fffffff00000001
> dtrace: pid 22849 has exited
> CPU     ID                    FUNCTION:NAME
>   20  46997                    main:getvalue In the D script value = 1
> 
> 
> Anyone have any idea what I''m doing wrong here (if anything)?
> 
> --
> - Keith
> _______________________________________________
> dtrace-discuss mailing list
> dtrace-discuss at opensolaris.org
-- 
Adam Leventhal, FishWorks                        http://blogs.sun.com/ahl