broke apart the Context[] stack into a linked-list with invokingConte…

…xt as parent pointer to caller. added call stack for trace.

src/vm/Context.java

@@ -2,11 +2,15 @@
 
 /** To call, push one of these and pop to return */
 public class Context {
+	Context invokingContext;	// parent in the stack or "caller"
+	FuncMetaData metadata;		// info about function we're executing
 	int returnip;
 	int[] locals; // args + locals, indexed from 0
 
-	public Context(int returnip, int nlocals) {
+	public Context(Context invokingContext, int returnip, FuncMetaData metadata) {
+		this.invokingContext = invokingContext;
 		this.returnip = returnip;
-		locals = new int[nlocals];
+		this.metadata = metadata;
+		locals = new int[metadata.nargs+metadata.nlocals];
 	}
 }

src/vm/Test.java

@@ -57,8 +57,11 @@ public class Test {
 	// PRINT "LOOPED "+N+" TIMES."
 			HALT					// 24
 	};
+	static FuncMetaData[] loop_metadata = {
+		new FuncMetaData("main", 0, 0, 0)
+	};
 
-	static int FACTORIAL_INDEX = 0;
+	static int FACTORIAL_INDEX = 1;
 	static int FACTORIAL_ADDRESS = 0;
 	static int MAIN_ADDRESS = 21;
 	static int[] factorial = {
@@ -88,15 +91,15 @@ public class Test {
 	};
 	static FuncMetaData[] factorial_metadata = {
 		//.def factorial: ARGS=1, LOCALS=0	ADDRESS
+		new FuncMetaData("main", 0, 0, MAIN_ADDRESS),
 		new FuncMetaData("factorial", 1, 0, FACTORIAL_ADDRESS)
 	};
 
-
 	static int[] f = {
 	//								ADDRESS
 	//.def main() { print f(10); }
 		ICONST, 10,					// 0
-		CALL, 0,					// 2
+		CALL, 1,					// 2
 		PRINT,						// 4
 		HALT,						// 5
 	//.def f(x): ARGS=1, LOCALS=1
@@ -110,22 +113,21 @@ public class Test {
 		RET
 	};
 	static FuncMetaData[] f_metadata = {
-		//.def factorial: ARGS=1, LOCALS=0	ADDRESS
+		new FuncMetaData("main", 0, 0, 0),
 		new FuncMetaData("f", 1, 1, 6)
 	};
 
 
 	public static void main(String[] args) {
-		VM vm = new VM(factorial, MAIN_ADDRESS, 0, factorial_metadata);
-		vm.trace = true;
-		vm.exec();
+		VM vm = new VM(factorial, 0, factorial_metadata);
+		vm.trace = false;
+		vm.exec(factorial_metadata[0].address);
 
-		vm = new VM(f, 0, 2, f_metadata);
-		vm.trace = true;
-		vm.exec();
+		vm = new VM(f, 2, f_metadata);
+		vm.exec(f_metadata[0].address);
+		vm.dumpDataMemory();
 
-		vm = new VM(loop, 0, 2, null);
-		vm.trace = true;
-		vm.exec();
+		vm = new VM(loop, 2, loop_metadata);
+		vm.exec(loop_metadata[0].address);
 	}
 }

src/vm/VM.java

@@ -32,15 +32,12 @@ public class VM {
 	// registers
 	int ip;             // instruction pointer register
 	int sp = -1;  		// stack pointer register
-	int callsp = -1;    // call stack pointer register
-
-	int startip = 0;	// where execution begins
 
 	// memory
 	int[] code;         // word-addressable code memory but still bytecodes.
 	int[] globals;      // global variable space
 	int[] stack;		// Operand stack, grows upwards
-	Context[] callstack;// call stack, grows upwards
+	Context ctx;		// the active context
 
 	/** Metadata about the functions allows us to refer to functions by
 	 * 	their index in this table. It makes code generation easier for
@@ -54,17 +51,16 @@ public class VM {
 
 	public boolean trace = false;
 
-	public VM(int[] code, int startip, int nglobals, FuncMetaData[] metadata) {
+	public VM(int[] code, int nglobals, FuncMetaData[] metadata) {
 		this.code = code;
-		this.startip = startip;
 		globals = new int[nglobals];
 		stack = new int[DEFAULT_STACK_SIZE];
-		callstack = new Context[DEFAULT_CALL_STACK_SIZE];
 		this.metadata = metadata;
 	}
 
-	public void exec() {
+	public void exec(int startip) {
 		ip = startip;
+		ctx = new Context(null,0,metadata[0]); // simulate a call to main()
 		cpu();
 	}
 
@@ -124,7 +120,7 @@ protected void cpu() {
 					break;
 				case STORE :
 					regnum = code[ip++];
-					callstack[callsp].locals[regnum] = stack[sp--];
+					ctx.locals[regnum] = stack[sp--];
 					break;
 				case GSTORE :
 					addr = code[ip++];
@@ -140,22 +136,22 @@ protected void cpu() {
 					// expects all args on stack
 					int findex = code[ip++];			// index of target function
 					int nargs = metadata[findex].nargs;	// how many args got pushed
-					int nlocals = metadata[findex].nlocals;
-					callstack[++callsp] = new Context(ip,nargs+nlocals);
+					ctx = new Context(ctx,ip,metadata[findex]);
 					// copy args into new context
 					for (int i=0; i<nargs; i++) {
-						callstack[callsp].locals[i] = stack[sp-i];
+						ctx.locals[i] = stack[sp-i];
 					}
 					sp -= nargs;
 					ip = metadata[findex].address;		// jump to function
 					break;
 				case RET:
-					ip = callstack[callsp--].returnip;
+					ip = ctx.returnip;
+					ctx = ctx.invokingContext;			// pop
 					break;
 				default :
 					throw new Error("invalid opcode: "+opcode+" at ip="+(ip-1));
 			}
-			if ( trace ) System.err.println(stackString());
+			if ( trace ) System.err.printf("%-22s %s\n", stackString(), callStackString());
 			opcode = code[ip];
 		}
 		if ( trace ) System.err.printf("%-35s", disInstr());
@@ -166,10 +162,10 @@ protected void cpu() {
     private void load() {
         int regnum;
         regnum = code[ip++];
-        stack[++sp] = callstack[callsp].locals[regnum];
+        stack[++sp] = ctx.locals[regnum];
     }
 
-    protected String stackString() {
+	protected String stackString() {
 		StringBuilder buf = new StringBuilder();
 		buf.append("stack=[");
 		for (int i = 0; i <= sp; i++) {
@@ -181,6 +177,18 @@ protected String stackString() {
 		return buf.toString();
 	}
 
+	protected String callStackString() {
+		List<String> stack = new ArrayList<String>();
+		Context c = ctx;
+		while ( c!=null ) {
+			if ( c.metadata!=null ) {
+				stack.add(0, c.metadata.name);
+			}
+			c = c.invokingContext;
+		}
+		return "calls="+stack.toString();
+	}
+
 	protected String disInstr() {
 		int opcode = code[ip];
 		String opName = Bytecode.instructions[opcode].name;