Stack-Based Linkage Convention

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The subroutine linkage conventions of MIPS include:

• Simple subroutine linkage as discussed previously


• Stack-based subroutine linkage convention discussed now


• Frame-based subroutine linkage convention where a stack frame is the section of the run-time stack that holds the data of a subroutine. It will not be covered in this course.

In the simple linkage convention, a subroutine is not able to call another subroutine because the return address in $ra is overwritten. The stack-based subroutine linkage convention can be used to solve the problem. The following picture shows the four sections of the stack-base subroutine linkage. The basic tasks of each section are

Subroutine call: Push all T registers that contain values that will be needed after the call. Put arguments in A registers. jal to the subroutine. Prolog: If this subroutine calls other subroutines, push $ra. Push all S registers that the subroutine alters. Body: Normal code, except that it must follow these conventions if it calls a subroutine. T registers and A registers can be used freely, as can any S registers that were saved in the prolog.

4. Epilog: Put return values in V registers. Pop any S registers. Pop $ra if it was pushed in the prolog. “jr $ra” back to the caller.


5. Regaining control: Pop any T registers that were previously pushed.