ptizoom has asked for the wisdom of the Perl Monks concerning the following question:

I run perl on a 64bit machine. I try callbacks of death, and pass some pointer to functions from (C to) perl back to C (using swig).... but the swig SvIV()/SvUV()/SvRV() seems to force it back to 32 bits. how annoying. are there any tricks I miss? 
 in perl
sub add_idle_callback($$)
{
    printf("\nadd_idle_callback x%x , x%x  \n", @_);
    &idle_callback_run(@_); # calls 
}

[download]
  in .swg
%typemap(in) void (* cb)(void *) {
   $1 = INT2PTR($1_ltype, SvUV($input));
   printf(":: x%x to x%x\n", (unsigned long long)SvUV($input), $1);

 if(SvGMAGICAL($input)) mg_get($input);
 $1 =  DPTR2FPTR($1_ltype, SvUV($input));
 printf("::DPTR2FPTR x%x to x%x\n", SvIV($input), $1);

}

[download]
  log
...
add_idle_callback x7ffb339f8040 , x0   <==== here in perl  the pointer
+ to function is 64bits
... 
<=========== but then swig- SvUV() or SvIV() cast it to 32 bits
:: x339f8040 to x339f8040  
::DPTR2FPTR x339f8040 to x339f8040 
....

[download]

Replies are listed 'Best First'.
Re: why SvUV() would crop to 32 bits?
by Anonymous Monk on Jan 03, 2015 at 21:13 UTC

    Check your C printf format. The %x corresponds to unsigned int, whereas long version %lx is probably indicated.

[reply]
[d/l]
[select]
      Or even better, perl provides the UVxf macro, which will be the correct format to print a UV; i.e. 
      printf(":: x%"UVxf" to ..."

      [download]

      Dave.

[reply]
[d/l]
        yes thanks...spot on. the macro woz working all the way, but just the format cropping let me down. (although I must have missed it with gdb.)

        so... 

          printf(":: x%" UVxf " to ...", SvUV($input), $1);

        [download]
        does the job.

        and here with a code example showing a few ugly ways to cast back pointers to all sorts...: 

        %typemap(in) void (* cb)(void *) , void *data , void (cb)(void *){
  //if SvGETMAGIC($input) {}; 
  $1 = INT2PTR($1_ltype, SvUV($input));
  printf(":: x%" UVxf " to x%lx\n", SvUV($input), $1);

  {
    int ret = SWIG_ConvertFunctionPtr($input, (void**)(& $1), 0);
    printf(":: to x%lx\n", $1);
  }

  if(SvGMAGICAL($input)) mg_get($input);
  $1 =  DPTR2FPTR($1_ltype, SvUV($input));
  printf("::DPTR2FPTR x%lx to x%lx\n", SvIV($input), $1);
}

        [download]
        bot::add_idle_callback x7fc3ff9bc040 , x0  
:: x7fc3ff9bc040 to x7fc3ff9bc040
:: to x7fc3ff9bc040
::DPTR2FPTR x7fc3ff9bc040 to x7fc3ff9bc040
:: x0 to x0
:: to x0
::DPTR2FPTR x0 to x0
::in c  add_idle_callback xff9bc040 , x0

        [download]

[reply]
[d/l]
[select]

Back to Seekers of Perl Wisdom