4.3 The Code Involved in a Simple Local Call

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A simple example is shown below; the procedure and the call to it are shown first in C (source code) and then in assembly. A more detailed, fully documented example is shown in Appendix A.

In C:

:
:
proc (50,100);   /* call to procedure 'proc'        */
:
:
proc (x,y)       /* function 'proc'                 */
int x,y;         /* returns the sum of two integers */
{
  return x+y;         
}
:
:

In assembly:

      :
      LD1  50, gr26       ; load arg word 0 into gr26
   ** BL   proc, gr2      ; branch (call) to 'proc'
      LD1  100, gr25      ; <delay slot>
                          ; load arg word 1 into gr25
      :
      :
proc: BV   0 (gr2)        ; branch (return) back to caller
      ADD  gr26,gr25,gr28 ; <delay slot>
                          ; add arguments,
                          ; put result into gr28
      :
** In instances where the target of the call is out of the range of the BL (i.e. greater than 256K bytes), there will be a slightly different code sequence. If this situation is identified at compile time, the compiler will generate a three-instruction sequence (LDIL,BLE,COPY) that is guaranteed to reach the target, instead of the BL. However, if the information is not known until link time (the compiler has already generated the BL), the BL will be linked to a "long branch stub" rather than to the actual procedure. This "stub" is merely the same two-instruction sequence that would have been used if the information had been known earlier.

4.2 Efficiency

Chapter 5 Inter-Module Procedure Calls

4.3 The Code Involved in a Simple Local Call

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