C typecast - difference between HPUX on IPF vs PA-RISC

[Yves Lagacé]

Here's a little C program:

#include

int main (int argc, char *argv [])
{
struct a bob
{
unsigned int var1 : 25 ; /* 1..24 */
unsigned int var2 : 2 ; /* 25..26 */
insigned int var3 : 5 ; /* 27..31 */
} ;

bob.var1 = 1 ;
bob.var2 = 0 ;
bob.var3 = 1 ;

printf ("var1 %d, var2 %d, bob %d\n",
bob.var1,
bob.bar2,
bob ) ;

printf ("var1 %d, var2 %d, bob %d\n",
bob.var1,
bob.bar2,
*((long *) &bob) ) ; /* typecast */

return (0) ;
}

On PA-RISC, the output is :
var1 1, var2 0, bob 129
var1 1, var2 0, bob 129

On Itaniun, I have the following output
var1 1, var2 0, bob 0
var1 1, var2 0, bob 129

Why is there a difference? I am missing a compilation switch?

[Mike Stroyan]

There is a difference because your code is passing a passing a struct by value, but telling printf that it got an int by value. That is broken. The results will depend on the details of the parameter passing conventions. They may also be affected by uninitialized register and stack values, since the called function is likely to look at locations that the caller did not set.

The calling conventions are documented in

"32-bit pa-risc run-time architecture"-
http://devresource.hp.com/drc/STK/docs/archive/rad_10_20.pdf

"64-Bit run-time architecture for PA-RISC 2.0"-
http://devresource.hp.com/drc/STK/docs/archive/pa64rt.pdf

"Itanium Software Conventions and Runtime Architecture"-
http://devresource.hp.com/drc/resources/ia64rt-12-gen.pdf