Static and Dynamic Relocation

Introduction

This shows the basic hardware instruction cycle for a machine that uses static relocation and for one that uses dynamic relocation.

Static Relocation

Static relocation refers to address transformations being done before execution of a program begins. A typical hardware instruction cycle looks like this:

loop
	w := M[instr_ctr];		(* fetch instruction *)
	oc := Opcode(w);
	adr := Address(w);
	instr_ctr := instr_ctr + 1;
	case oc of
	1:	reg := reg+M[adr];	(* add *)
	2:	M[adr] := reg;		(* store *)
	3:	instr_ctr := adr;	(* branch *)
	...
	end
end (* loop *)

Dynamic Relocation

Dynamic relocation refers to address transformations being done during execution of a program. In what follows, the function NL_map (for Name Location map) maps the relocatable (virtual) address va given in the program into the real (physical) storage address pa:

pa := NL_map(va)

loop
	w := M[NL_map(instr_ctr)];		(* fetch instruction *)
	oc := Opcode(w);
	adr := Address(w);
	instr_ctr := instr_ctr + 1;
	case oc of
	1:	reg := reg+M[NL_map(adr)];	(* add *)
	2:	M[NL_map(adr)] := reg;		(* store *)
	3:	instr_ctr := NL_map(adr);	(* branch *)
	...
	end
end (* loop *)