2003/09/18 08:10:36
[org.ibex.core.git] / src / org / xwt / mips / Interpreter.java
diff --git a/src/org/xwt/mips/Interpreter.java b/src/org/xwt/mips/Interpreter.java
new file mode 100644 (file)
index 0000000..ddc4d69
--- /dev/null
@@ -0,0 +1,1694 @@
+// Copyright 2003 Adam Megacz
+// Author Brian Alliet
+// Based on org.xwt.imp.MIPS by Adam Megacz
+
+package org.xwt.imp;
+
+import java.io.*;
+
+public class MIPSInterpreter extends MIPSEmu {
+
+    // Registers
+    private int[] registers = new int[32];
+    private int hi,lo;
+    
+    // Floating Point Registers
+    private int[] fpregs = new int[32];
+
+    // 24-31 - unused
+    // 23    - conditional bit
+    // 18-22 - unused
+    // 12-17 - cause bits (unimplemented)
+    // 7-11  - enables bits (unimplemented)
+    // 2-6   - flags (unimplemented)
+    // 0-1   - rounding mode (only implemented for fixed point conversions)
+    private int fcsr;
+    
+    private int nextPC;
+    
+    // The filename if the binary we're running
+    private String image;
+    
+    // Register Operations
+    private final void setFC(boolean b) { fcsr = (fcsr&~0x800000) | (b ? 0x800000 : 0x000000); }
+    private final int roundingMode() { return fcsr & 3; /* bits 0-1 */ }
+    private final double getDouble(int r) {
+        return Double.longBitsToDouble(((fpregs[r+1]&0xffffffffL) << 32) | (fpregs[r]&0xffffffffL));
+    }
+    private final void setDouble(int r, double d) {
+        long l = Double.doubleToLongBits(d);
+        fpregs[r+1] = (int)(l >>> 32); fpregs[r] = (int)l;
+    }
+    private final float getFloat(int r) { return Float.intBitsToFloat(fpregs[r]); }
+    private final void setFloat(int r, float f) { fpregs[r] = Float.floatToRawIntBits(f); }
+    
+    // Main run loop
+    public void execute() throws EmulationException {
+        int[] r = registers;
+        if(state == PAUSED) state = RUNNING;
+        if(state != RUNNING) throw new IllegalStateException("execute() called in inappropriate state");
+        runSome(nextPC);
+    }
+    
+    // Main interpretor (also used for compilation)
+    // the return value is meaningless, its just to catch people typing "return" by accident
+    private int runSome(int pc) throws FaultException,EmulationException {
+        int[] r = registers;
+        int[] f = fpregs;
+        int nextPC = pc + 4;
+    try {
+    OUTER: for(;;) {
+        int insn;
+        try {
+            insn = readPages[pc>>>PAGE_SHIFT][(pc>>>2)&PAGE_WORDS-1];
+        } catch (RuntimeException e) {
+            insn = memRead(pc);
+        }
+
+        int op = (insn >>> 26) & 0xff;                 // bits 26-31
+        int rs = (insn >>> 21) & 0x1f;                 // bits 21-25
+        int rt = (insn >>> 16) & 0x1f;                 // bits 16-20 
+        int ft = (insn >>> 16) & 0x1f;
+        int rd = (insn >>> 11) & 0x1f;                 // bits 11-15
+        int fs = (insn >>> 11) & 0x1f;
+        int shamt = (insn >>> 6) & 0x1f;               // bits 6-10
+        int fd = (insn >>> 6) & 0x1f;
+        int subcode = insn & 0x3f;                     // bits 0-5  
+
+        int jumpTarget = (insn & 0x03ffffff);          // bits 0-25
+        int unsignedImmediate = insn & 0xffff;
+        int signedImmediate = (insn << 16) >> 16;
+        int branchTarget = signedImmediate;
+
+        int tmp, addr; // temporaries
+        
+        r[ZERO] = 0;
+    
+        switch(op) {
+            case 0: {
+                switch(subcode) {
+                    case 0: // SLL
+                        if(insn == 0) break;
+                        r[rd] = r[rt] << shamt;
+                        break;
+                    case 2: // SRL
+                        r[rd] = r[rt] >>> shamt;
+                        break;
+                    case 3: // SRA
+                        r[rd] = r[rt] >> shamt;
+                        break;
+                    // FIXME: Do we need % 32 on the r[rs] ?
+                    case 4: // SLLV
+                        r[rd] = r[rt] << r[rs];
+                        break;
+                    case 6: // SRLV
+                        r[rd] = r[rt] >>> r[rs];
+                        break;
+                    case 7: // SRAV
+                        r[rd] = r[rt] >> r[rs];
+                        break;
+                    case 8: // JR
+                        tmp = r[rs]; pc += 4; nextPC = tmp;
+                        continue OUTER;
+                    case 9: // JALR
+                        tmp = r[rs]; pc += 4; r[rd] = pc+4; nextPC = tmp;
+                        continue OUTER;
+                    case 12: // SYSCALL
+                        r[V0] = syscall(r[V0],r[A0],r[A1],r[A2],r[A3]);
+                        if(state != RUNNING) {
+                            this.nextPC = nextPC;
+                            break OUTER;
+                        }
+                        break;
+                    case 13: // BREAK
+                        throw new EmulationException("Break");
+                    case 16: // MFHI
+                        r[rd] = hi;
+                        break;
+                    case 17: // MTHI
+                        hi = r[rs];
+                        break;
+                    case 18: // MFLO
+                        r[rd] = lo;
+                        break;
+                    case 19: // MTLO
+                        lo = r[rs];
+                        break;
+                    case 24: { // MULT
+                        long hilo = (long)(r[rs]) * ((long)r[rt]);
+                        hi = (int) (hilo >>> 32);
+                        lo = (int) hilo;
+                        break;
+                    }
+                    case 25: { // MULTU
+                        long hilo = (r[rs] & 0xffffffffL) * (r[rt] & 0xffffffffL);
+                        hi = (int) (hilo >>> 32);
+                        lo = (int) hilo;
+                        break;
+                    }
+                    case 26: // DIV
+                        hi = r[rs]%r[rt];
+                        lo = r[rs]/r[rt];
+                        break;
+                    case 27: // DIVU
+                        hi = (int)((r[rs] & 0xffffffffL) % (r[rt] & 0xffffffffL));
+                        lo = (int)((r[rs] & 0xffffffffL) / (r[rt] & 0xffffffffL));
+                        break;
+                    case 32: // ADD
+                        r[rd] = r[rs] + r[rt]; // FIXME: Trap on overflow
+                        break;
+                    case 33: // ADDU
+                        r[rd] = r[rs] + r[rt];
+                        break;
+                    case 34: // SUB
+                        r[rd] = r[rs] - r[rt]; // FIXME: Trap on overflow
+                        break;
+                    case 35: // SUBU
+                        r[rd] = r[rs] - r[rt];
+                        break;
+                    case 36: // AND
+                        r[rd] = r[rs] & r[rt];
+                        break;
+                    case 37: // OR
+                        r[rd] = r[rs] | r[rt];
+                        break;
+                    case 38: // XOR
+                        r[rd] = r[rs] ^ r[rt];
+                        break;
+                    case 39: // NOR
+                        r[rd] = ~(r[rs] | r[rt]);
+                        break;
+                    case 42: // SLT
+                        r[rd] = r[rs] < r[rt] ? 1 : 0;
+                        break;
+                    case 43: // SLTU
+                        r[rd] = ((r[rs] & 0xffffffffL) < (r[rt] & 0xffffffffL)) ? 1 : 0;
+                        break;
+                    default:
+                        throw new EmulationException("Illegal instruction 0/" + subcode);
+                }
+                break;
+            }
+            case 1: {
+                switch(rt) {
+                    case 0: // BLTZ
+                        if(r[rs] < 0) {
+                            pc += 4; tmp = pc + branchTarget*4; nextPC = tmp;                   
+                            continue OUTER;
+                        }
+                        break;
+                    case 1: // BGEZ
+                        if(r[rs] >= 0) {
+                            pc += 4; tmp = pc + branchTarget*4; nextPC = tmp;
+                            continue OUTER;
+                        }
+                        break;
+                    case 16: // BLTZAL
+                        if(r[rs] < 0) {
+                            pc += 4; r[RA] = pc+4; tmp = pc + branchTarget*4; nextPC = tmp;
+                            continue OUTER;
+                        }
+                        break;
+                    case 17: // BGEZAL
+                        if(r[rs] >= 0) {
+                            pc += 4; r[RA] = pc+4; tmp = pc + branchTarget*4; nextPC = tmp;  
+                            continue OUTER;
+                        }
+                        break;
+                    default:
+                        throw new EmulationException("Illegal Instruction");
+                }
+                break;
+            }
+            case 2: { // J
+                tmp = (pc&0xf0000000) | (jumpTarget << 2);
+                pc+=4; nextPC = tmp;
+                continue OUTER;
+            }
+            case 3: { // JAL
+                tmp = (pc&0xf0000000) | (jumpTarget << 2);
+                pc+=4; r[RA] = pc+4; nextPC = tmp;
+                continue OUTER;
+            }
+            case 4: // BEQ
+                if(r[rs] == r[rt]) {
+                    pc += 4; tmp = pc + branchTarget*4; nextPC = tmp;
+                    continue OUTER;
+                }
+                break;
+            case 5: // BNE                
+                if(r[rs] != r[rt]) {
+                    pc += 4; tmp = pc + branchTarget*4; nextPC = tmp; 
+                    continue OUTER;
+                }
+                break;
+            case 6: //BLEZ
+                if(r[rs] <= 0) {
+                    pc += 4; tmp = pc + branchTarget*4; nextPC = tmp;
+                    continue OUTER;
+                }
+                break;
+            case 7: //BGTZ
+                if(r[rs] > 0) {
+                    pc += 4; tmp = pc + branchTarget*4; nextPC = tmp;
+                    continue OUTER;
+                }
+                break;
+            case 8: // ADDI
+                r[rt] = r[rs] + signedImmediate;
+                break;
+            case 9: // ADDIU
+                r[rt] = r[rs] + signedImmediate;
+                break;
+            case 10: // SLTI
+                r[rt] = r[rs] < signedImmediate ? 1 : 0;
+                break;
+            case 11: // SLTIU
+                r[rt] = (r[rs]&0xffffffffL) < (unsignedImmediate&0xffffffffL) ? 1 : 0;
+                break;
+            case 12: // ANDI
+                r[rt] = r[rs] & unsignedImmediate;
+                break;
+            case 13: // ORI
+                r[rt] = r[rs] | unsignedImmediate;
+                break;
+            case 14: // XORI
+                r[rt] = r[rs] ^ unsignedImmediate;
+                break;
+            case 15: // LUI
+                r[rt] = unsignedImmediate << 16;
+                break;
+            case 16:
+                throw new EmulationException("TLB/Exception support not implemented");
+            case 17: { // FPU
+                boolean debug = false;
+                String line = debug ? sourceLine(pc) : "";
+                boolean debugon = debug && (line.indexOf("dtoa.c:51") >= 0 || line.indexOf("dtoa.c:52") >= 0 || line.indexOf("test.c") >= 0);
+                if(rs > 8 && debugon)
+                    System.out.println("               FP Op: " + op + "/" + rs + "/" + subcode + " " + line);
+                // FIXME: This could probably be removed. I don't think gcc will ever generate code that does this
+                if(roundingMode() != 0 && rs != 6 /*CTC.1*/ && !((rs==16 || rs==17) && subcode == 36 /* CVT.W.Z */))
+                    throw new EmulationException("Non-cvt.w.z operation attempted with roundingMode != round to nearest");
+                switch(rs) {
+                    case 0: // MFC.1
+                        r[rt] = f[rd];
+                        break;
+                    case 2: // CFC.1
+                        if(fs != 31) throw new EmulationException("FCR " + fs + " unavailable");
+                        r[rt] = fcsr;
+                        break;
+                    case 4: // MTC.1
+                        f[rd] = r[rt];
+                        break;
+                    case 6: // CTC.1
+                        if(fs != 31) throw new EmulationException("FCR " + fs + " unavailable");
+                        fcsr = r[rt];   
+                        break;
+                    case 8: // BC1F, BC1T
+                        if(((fcsr&0x800000)!=0) == (((insn>>>16)&1)!=0)) {
+                            pc += 4; tmp = pc + branchTarget*4; nextPC = tmp;
+                            continue OUTER;
+                        }
+                        break;
+                    case 16: {  // Single
+                        switch(subcode) {
+                            case 0: // ADD.S
+                                setFloat(fd,getFloat(fs)+getFloat(ft));
+                                break;
+                            case 1: // SUB.S
+                                setFloat(fd,getFloat(fs)-getFloat(ft));
+                                break;
+                            case 2: // MUL.S
+                                setFloat(fd,getFloat(fs)*getFloat(ft));
+                                break;
+                            case 3: // DIV.S
+                                setFloat(fd,getFloat(fs)/getFloat(ft));
+                                break;
+                            case 5: // ABS.S
+                                setFloat(fd,Math.abs(getFloat(fs)));
+                                break;
+                            case 6: // MOV.S
+                                f[fd] = f[fs];
+                                break;
+                            case 7: // NEG.S
+                                setFloat(fd,-getFloat(fs)); // FIXME: just flip the sign bit
+                                break;
+                            case 33: // CVT.D.S
+                                setDouble(fd,getFloat(fs));
+                                break;
+                            case 36: // CVT.W.S
+                                switch(roundingMode()) {
+                                    case 0: f[fd] = (int)Math.floor(getFloat(fs)+0.5f); break; // Round to nearest
+                                    case 1: f[fd] = (int)getFloat(fs); break; // Round towards zero
+                                    case 2: f[fd] = (int)Math.ceil(getFloat(fs)); break; // Round towards plus infinity
+                                    case 3: f[fd] = (int)Math.floor(getFloat(fs)); break; // Round towards minus infinity
+                                }
+                                break;
+                            case -50: // C.EQ.S
+                                setFC(getFloat(fs) == getFloat(ft)); // FIXME: just compare the ints, be sure things are normalized
+                                break;
+                            case 60: // C.LT.S
+                                setFC(getFloat(fs) < getFloat(ft));
+                                break;
+                            default: throw new EmulationException("Invalid Instruction 17/" + rs + "/" + subcode + " at " + sourceLine(pc));
+                        }
+                        break;
+                    }
+                    case 17: { // Double
+                        switch(subcode) {
+                            case 0: // ADD.D
+                                setDouble(fd,getDouble(fs)+getDouble(ft));
+                                break;
+                            case 1: // SUB.D
+                                if(debugon) System.out.println("f" + fd + " = f" + fs + " (" + getDouble(fs) + ") - f" + ft + " (" + getDouble(ft) + ")");
+                                setDouble(fd,getDouble(fs)-getDouble(ft));
+                                break;
+                            case 2: // MUL.D
+                                if(debugon) System.out.println("f" + fd + " = f" + fs + " (" + getDouble(fs) + ") * f" + ft + " (" + getDouble(ft) + ")");
+                                setDouble(fd,getDouble(fs)*getDouble(ft));
+                                if(debugon) System.out.println("f" + fd + " = " + getDouble(fd));
+                                break;
+                            case 3: // DIV.D
+                                setDouble(fd,getDouble(fs)/getDouble(ft));
+                                break;
+                            case 5: // ABS.D
+                                setDouble(fd,Math.abs(getDouble(fs)));
+                                break;
+                            case 6: // MOV.D
+                                f[fd] = f[fs];
+                                f[fd+1] = f[fs+1];
+                                break;
+                            case 7: // NEG.D
+                                setDouble(fd,-getDouble(fs)); // FIXME: just flip the sign bit
+                                break;
+                            case 32: // CVT.S.D
+                                setFloat(fd,(float)getDouble(fs));
+                                break;
+                            case 36: // CVT.W.D
+                                if(debugon) System.out.println("CVT.W.D rm: " + roundingMode() + " f" + fs + ":" + getDouble(fs));
+                                switch(roundingMode()) {
+                                    case 0: f[fd] = (int)Math.floor(getDouble(fs)+0.5); break; // Round to nearest
+                                    case 1: f[fd] = (int)getDouble(fs); break; // Round towards zero
+                                    case 2: f[fd] = (int)Math.ceil(getDouble(fs)); break; // Round towards plus infinity
+                                    case 3: f[fd] = (int)Math.floor(getDouble(fs)); break; // Round towards minus infinity
+                                }
+                                if(debugon) System.out.println("CVT.W.D: f" + fd + ":" + f[fd]);
+                                break;
+                            case 50: // C.EQ.D
+                                setFC(getDouble(fs) == getDouble(ft)); // FIXME: just compare the ints, be sure things are normalized
+                                break;
+                            case 60: // C.LT.D
+                                setFC(getDouble(fs) < getDouble(ft));
+                                break;
+                            case 62: // C.LE.D
+                                setFC(getDouble(fs) <= getDouble(ft));
+                                break;                                
+                            default: throw new EmulationException("Invalid Instruction 17/" + rs + "/" + subcode + " at " + sourceLine(pc));
+                        }
+                        break;
+                    }
+                    case 20: { // Integer
+                        switch(subcode) {
+                            case 33: // CVT.D.W
+                                setDouble(fd,(double)f[fs]);
+                                break;
+                            default: throw new EmulationException("Invalid Instruction 17/" + rs + "/" + subcode + " at " + sourceLine(pc));
+                        }
+                        break;
+                    }
+                    default:
+                        throw new EmulationException("Invalid Instruction 17/" + rs);
+                }
+                break;
+            }
+            case 18: case 19:
+                throw new EmulationException("No coprocessor installed");
+            case 32: { // LB
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&3) {
+                    case 0: tmp = (tmp>>>24)&0xff; break;
+                    case 1: tmp = (tmp>>>16)&0xff; break;
+                    case 2: tmp = (tmp>>> 8)&0xff; break;
+                    case 3: tmp = (tmp>>> 0)&0xff; break;
+                }
+                if((tmp&0x80)!=0) tmp |= 0xffffff00; // sign extend
+                r[rt] = tmp;
+                break;
+            }
+            case 33: { // LH
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&2) {
+                    case 0: tmp = (tmp>>>16)&0xffff; break;
+                    case 2: tmp = (tmp>>> 0)&0xffff; break;
+                }
+                if((tmp&0x8000)!=0) tmp |= 0xffff0000; // sign extend
+                r[rt] = tmp;
+                break;              
+            }
+            case 34: { // LWL;
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&3) {
+                    case 0: r[rt] = (r[rt]&0x00000000)|(tmp<< 0); break;
+                    case 1: r[rt] = (r[rt]&0x000000ff)|(tmp<< 8); break;
+                    case 2: r[rt] = (r[rt]&0x0000ffff)|(tmp<<16); break;
+                    case 3: r[rt] = (r[rt]&0x00ffffff)|(tmp<<24); break;
+                }
+                break;
+            }
+            case 35: // LW
+                addr = r[rs] + signedImmediate;
+                try {
+                    r[rt] = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    r[rt] = memRead(addr);
+                }
+                break;
+            case 36: { // LBU
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr);
+                }
+                switch(addr&3) {
+                    case 0: r[rt] = (tmp>>>24)&0xff; break;
+                    case 1: r[rt] = (tmp>>>16)&0xff; break;
+                    case 2: r[rt] = (tmp>>> 8)&0xff; break;
+                    case 3: r[rt] = (tmp>>> 0)&0xff; break;
+                }
+                break;
+            }
+            case 37: { // LHU
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&2) {
+                    case 0: r[rt] = (tmp>>>16)&0xffff; break;
+                    case 2: r[rt] = (tmp>>> 0)&0xffff; break;
+                }
+                break;
+            }
+            case 38: { // LWR
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&3) {
+                    case 0: r[rt] = (r[rt]&0xffffff00)|(tmp>>>24); break;
+                    case 1: r[rt] = (r[rt]&0xffff0000)|(tmp>>>16); break;
+                    case 2: r[rt] = (r[rt]&0xff000000)|(tmp>>> 8); break;
+                    case 3: r[rt] = (r[rt]&0x00000000)|(tmp>>> 0); break;
+                }
+                break;
+            }
+            case 40: { // SB
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&3) {
+                    case 0: tmp = (tmp&0x00ffffff) | ((r[rt]&0xff)<<24); break;
+                    case 1: tmp = (tmp&0xff00ffff) | ((r[rt]&0xff)<<16); break;
+                    case 2: tmp = (tmp&0xffff00ff) | ((r[rt]&0xff)<< 8); break;
+                    case 3: tmp = (tmp&0xffffff00) | ((r[rt]&0xff)<< 0); break;
+                }
+                try {
+                    writePages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1] = tmp;
+                } catch(RuntimeException e) {
+                    memWrite(addr&~3,tmp);
+                }
+                break;
+            }
+            case 41: { // SH
+                addr = r[rs] + signedImmediate;
+                try {
+                    tmp = readPages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1];
+                } catch(RuntimeException e) {
+                    tmp = memRead(addr&~3);
+                }
+                switch(addr&2) {
+                    case 0: tmp = (tmp&0x0000ffff) | ((r[rt]&0xffff)<<16); break;
+                    case 2: tmp = (tmp&0xffff0000) | ((r[rt]&0xffff)<< 0); break;
+                }
+                try {
+                    writePages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1] = tmp;
+                } catch(RuntimeException e) {
+                    memWrite(addr&~3,tmp);
+                }
+                break;
+            }
+            case 42: { // SWL
+                addr = r[rs] + signedImmediate;
+                tmp = memRead(addr&~3);
+                switch(addr&3) {
+                    case 0: tmp=(tmp&0x00000000)|(r[rt]>>> 0); break;
+                    case 1: tmp=(tmp&0xff000000)|(r[rt]>>> 8); break;
+                    case 2: tmp=(tmp&0xffff0000)|(r[rt]>>>16); break;
+                    case 3: tmp=(tmp&0xffffff00)|(r[rt]>>>24); break;
+                }
+                try {
+                    writePages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1] = tmp;
+                } catch(RuntimeException e) {
+                    memWrite(addr&~3,tmp);
+                }
+                break;
+            }
+            case 43: // SW
+                addr = r[rs] + signedImmediate;
+                try {
+                    writePages[addr>>>PAGE_SHIFT][(addr>>>2)&PAGE_WORDS-1] = r[rt];
+                } catch(RuntimeException e) {
+                    memWrite(addr&~3,r[rt]);
+                }
+                break;
+            case 46: { // SWR
+                addr = r[rs] + signedImmediate;
+                tmp = memRead(addr&~3);
+                switch(addr&3) {
+                    case 0: tmp=(tmp&0x00ffffff)|(r[rt]<<24); break;
+                    case 1: tmp=(tmp&0x0000ffff)|(r[rt]<<16); break;
+                    case 2: tmp=(tmp&0x000000ff)|(r[rt]<< 8); break;
+                    case 3: tmp=(tmp&0x00000000)|(r[rt]<< 0); break;
+                }
+                memWrite(addr&~3,tmp);
+                break;
+            }
+            case 49: // LWC1
+                f[rt] = memRead(r[rs] + signedImmediate);
+                break;
+            case 57: // SWC1
+                memWrite(r[rs] + signedImmediate,f[rt]);
+                break;
+            default:
+                throw new EmulationException("Invalid Instruction: " + op);
+        }
+        pc = nextPC;
+        nextPC = pc + 4;
+    } // for(;;)
+    } catch(EmulationException e) {
+        this.nextPC = pc;
+        throw e;
+    }
+        return 0;
+    }
+    
+    // Image loading function
+    void loadImage(String file) throws IOException {
+        ELF elf = new ELF(file);
+        if(elf.header.type != ELF.ELFHeader.ET_EXEC)
+            throw new IOException("Binary is not an executable");
+        if(elf.header.machine != ELF.ELFHeader.EM_MIPS)
+            throw new IOException("Binary is not for the MIPS I Architecture");
+        entryPoint = elf.header.entry;
+        ELF.PHeader[] pheaders = elf.pheaders;
+        brk = 0;
+        for(int i=0;i<pheaders.length;i++) {
+            ELF.PHeader ph = pheaders[i];
+            if(ph.type != ELF.PHeader.PT_LOAD) continue;
+            int memsize = ph.memsz;
+            int filesize = ph.filesz;
+            if(memsize == 0) continue;
+            if(memsize < 0) throw new IOException("pheader size too large");
+            int addr = ph.vaddr;
+            if(addr == 0x0) throw new IOException("pheader vaddr == 0x0");
+            if(addr+memsize >= (brk<<PAGE_SHIFT)) brk = (addr+memsize+PAGE_SIZE-1) >> PAGE_SHIFT;
+            
+            for(int j=0;j<memsize+PAGE_SIZE-1;j+=PAGE_SIZE) {
+                int page = (j+addr) >>> PAGE_SHIFT;
+                if(readPages[page] == null)
+                    readPages[page] = new int[PAGE_WORDS];
+                if(ph.writable()) writePages[page] = readPages[page];
+            }
+            if(filesize != 0) {
+                filesize = filesize & ~3;
+                DataInputStream dis = new DataInputStream(ph.getInputStream());
+                do {
+                    readPages[addr >>> PAGE_SHIFT][(addr >>> 2)&(PAGE_WORDS-1)] = dis.readInt();
+                    addr+=4;
+                    filesize-=4;
+                } while(filesize > 0);
+                dis.close();
+            }
+        }
+        image = file;
+        state = INITIALIZED;
+    }
+    
+    protected void _start(int pc) {
+        registers[SP] = INITIAL_SP;
+        registers[RA] = 0xdeadbeef;
+        nextPC = pc;
+    }
+    public MIPSInterpreter() { }
+    public MIPSInterpreter(String image) throws IOException { loadImage(image); }
+    
+    // Debug functions
+    // NOTE: This probably requires a jdk > 1.1, however, it is only used for debugging
+    public String sourceLine(int pc) {
+        final String addr2line = "mips-unknown-elf-addr2line";
+        String line;
+        if(image==null) return null;
+        try {
+            Process p = Runtime.getRuntime().exec(new String[]{addr2line,"-e",image,toHex(pc)});
+            line = new BufferedReader(new InputStreamReader(p.getInputStream())).readLine();
+            if(line == null) return null;
+            while(line.startsWith("../")) line = line.substring(3);
+            return line;
+        } catch(IOException e) {
+            return null;
+        }
+    }
+    
+    public class DebugShutdownHook implements Runnable {
+        public void run() {
+            int pc = nextPC;
+            if(getState() == RUNNING)
+                System.err.print("\nCPU Executing " + toHex(pc) + ": " + sourceLine(pc) + "\n");
+        }
+    }
+
+    public static void main(String[] argv) throws Exception {
+        String image = argv[0];
+        MIPSInterpreter emu = new MIPSInterpreter();
+        emu.loadImage(image);
+        Runtime.getRuntime().addShutdownHook(new Thread(emu.new DebugShutdownHook()));
+        // User data
+        int addr = emu.sbrk(PAGE_SIZE);
+        for(int i=0;i<10;i++) {
+            String s = "User Info item: " + (i+1) + "\0";
+            byte[] b = s.getBytes("US-ASCII");
+            emu.copyout(b,addr,b.length);
+            emu.setUserInfo(i,addr);
+            addr += b.length;
+        }
+        // End user data
+        int status = emu.run(argv);
+        System.err.println("Exit status: " + status);
+        System.exit(status);
+    }
+}
+
+abstract class MIPSEmu implements Syscalls, Errno {
+    // Register Names
+    protected final static int ZERO = 0; // Immutable, hardwired to 0
+    protected final static int AT = 1;  // Reserved for assembler
+    protected final static int K0 = 26; // Reserved for kernel 
+    protected final static int K1 = 27; // Reserved for kernel 
+    protected final static int GP = 28; // Global pointer (the middle of .sdata/.sbss)
+    protected final static int SP = 29; // Stack pointer
+    protected final static int FP = 30; // Frame Pointer
+    protected final static int RA = 31; // Return Address
+    
+    // Return values (caller saved)
+    protected final static int V0 = 2;
+    protected final static int V1 = 3;
+    // Argument Registers (caller saved)
+    protected final static int A0 = 4; 
+    protected final static int A1 = 5;
+    protected final static int A2 = 6;
+    protected final static int A3 = 7;
+    // Temporaries (caller saved)
+    protected final static int T0 = 8;
+    protected final static int T1 = 9;
+    protected final static int T2 = 10;
+    protected final static int T3 = 11;
+    protected final static int T4 = 12;
+    protected final static int T5 = 13;
+    protected final static int T6 = 14;
+    protected final static int T7 = 15;
+    protected final static int T8 = 24;
+    protected final static int T9 = 25;
+    // Saved (callee saved)
+    protected final static int S0 = 16;
+    protected final static int S1 = 17;
+    protected final static int S2 = 18;
+    protected final static int S3 = 19;
+    protected final static int S4 = 20;
+    protected final static int S5 = 21;
+    protected final static int S6 = 22;
+    protected final static int S7 = 23;
+
+    // Page Constants
+    // Page Size: 4k
+    // Total Pages: 64k
+    // Maxiumum Addressable memory 256mb
+    // 1mb of stack space
+    protected final static int PAGE_SIZE = 4096;
+    protected final static int PAGE_WORDS = (int)(PAGE_SIZE >>> 2);
+    protected final static int PAGE_SHIFT = 12;
+    protected final static int STACK_PAGES = 256;
+    // NOTE: If you change TOTAL_PAGES crt0.c needs to be updated to reflect the
+    // new location of INITIAL_SP
+    protected final static int TOTAL_PAGES = 65536;
+    protected final static int BRK_LIMIT = 32768;
+    // Top page is always empty
+    // next page down contains command line arguments
+    protected final static int ARGS_ADDR = (TOTAL_PAGES-2)*PAGE_SIZE;
+    // next page down contains _user_info data
+    protected final static int USER_INFO_ADDR = (TOTAL_PAGES-3)*PAGE_SIZE;
+    // next page down is the start of the stack
+    protected final static int INITIAL_SP = (TOTAL_PAGES-3)*PAGE_SIZE;
+    // magic page that signified an allocated but empty (untouched) page
+    private final static int[] emptyPage = new int[0];
+    
+    // Main memory
+    protected final int[][] readPages;
+    protected final int[][] writePages;
+    
+    // Brk
+    protected int brk; // PAGE not address
+        
+    // Entry point - what start() sets pc to
+    protected int entryPoint;
+    
+    // State constants
+    public final static int UNINITIALIZED = 0;
+    public final static int INITIALIZED = 1;
+    public final static int RUNNING = 2;
+    public final static int PAUSED = 3;
+    public final static int DONE = 4;
+    
+    // State
+    protected int state = UNINITIALIZED;
+    public final int getState() { return state; }
+    protected int exitStatus;
+    
+    // File descriptors
+    private final static int OPEN_MAX = 256;
+    private FileDescriptor[] fds;
+    
+    // Temporary buffer for read/write operations
+    private byte[] _byteBuf = null;
+    private final static int MAX_CHUNK = 4*1024*1024-8;
+    
+    // Abstract methods
+    // This should start executing at pc
+    public abstract void execute() throws EmulationException;
+    // This should initialize the cpu registers to point to the entry point
+    protected abstract void _start(int pc);
+   
+    public static final int PID = 1;
+    
+    public MIPSEmu() {
+        readPages = new int[TOTAL_PAGES][];
+        writePages = new int[TOTAL_PAGES][];
+        for(int i=0;i<STACK_PAGES;i++)
+            readPages[TOTAL_PAGES-1-i] = writePages[TOTAL_PAGES-1-i] = emptyPage;
+    }
+    
+    public void copyin(int addr, byte[] a, int length) throws ReadFaultException {
+        int n=0;
+        if((addr&3)!=0) {
+            int word = memRead(addr&~3);
+             switch(addr&3) {
+                case 1: a[n++] = (byte)((word>>>16)&0xff); if(length-n==0) break;
+                case 2: a[n++] = (byte)((word>>> 8)&0xff); if(length-n==0) break;
+                case 3: a[n++] = (byte)((word>>> 0)&0xff); if(length-n==0) break;
+            }
+            addr = (addr&~3)+4;
+        }
+        while(length-n > 3) {
+            int start = (addr&(PAGE_SIZE-1))>>2;
+            int end = start + (min(PAGE_SIZE-(addr&(PAGE_SIZE-1)),(length-n)&~3) >> 2);
+            int[] page = readPages[addr >>> PAGE_SHIFT];
+            if(page == null) throw new ReadFaultException(addr);
+            if(page == emptyPage) { addr+=(end-start); n+=(end-start); continue; }
+            for(int i=start;i<end;i++,addr+=4) {
+                int word = page[i];
+                a[n++] = (byte)((word>>>24)&0xff); a[n++] = (byte)((word>>>16)&0xff);
+                a[n++] = (byte)((word>>> 8)&0xff); a[n++] = (byte)((word>>> 0)&0xff);
+            }
+        }
+        if(length-n > 0) {
+            int word = memRead(addr);
+            if(length-n >= 1) a[n] = (byte)((word>>>24)&0xff);
+            if(length-n >= 2) a[n+1] = (byte)((word>>>16)&0xff);
+            if(length-n >= 3) a[n+2] = (byte)((word>>> 8)&0xff);
+        }
+    }
+    
+    public void copyout(byte[] a, int addr, int length) throws FaultException {
+        int n=0;
+        if((addr&3)!=0) {
+            int word = memRead(addr&~3);
+             switch(addr&3) {
+                case 1: word = (word&0xff00ffff)|((a[n]&0xff)<<16); n++; if(length-n==0) break;
+                case 2: word = (word&0xffff00ff)|((a[n]&0xff)<< 8); n++; if(length-n==0) break;
+                case 3: word = (word&0xffffff00)|((a[n]&0xff)<< 0); n++; if(length-n==0) break;
+            }
+            memWrite(addr&~3,word);
+            addr = (addr&~3)+4;
+        }
+        
+        while(length-n > 3) {
+            int start = (addr&(PAGE_SIZE-1))>>2;
+            int end = start + (min(PAGE_SIZE-(addr&(PAGE_SIZE-1)),(length-n)&~3) >> 2);
+            int[] page = writePages[addr >>> PAGE_SHIFT];
+            if(page == null) throw new WriteFaultException(addr);
+            if(page == emptyPage) { memWrite(addr,0); page = writePages[addr >>> PAGE_SHIFT]; }
+            for(int i=start;i<end;i++,addr+=4) {
+                int word = ((a[n+0]&0xff)<<24)|((a[n+1]&0xff)<<16)|((a[n+2]&0xff)<<8)|((a[n+3]&0xff)<<0); n+=4;
+                page[i] = word;
+            }
+        }
+        if(length-n > 0) {
+            int word = memRead(addr);
+            word = (word&0x00ffffff)|((a[n]&0xff)<<24);
+            if(length-n > 1) { word = (word&0xff00ffff)|((a[n+1]&0xff)<<16); }
+            if(length-n > 2) { word = (word&0xffff00ff)|((a[n+2]&0xff)<< 8); }
+            memWrite(addr,word);
+        }
+    }
+    
+    protected final int memRead(int addr) throws ReadFaultException  {
+        if((addr & 3) != 0) throw new ReadFaultException(addr);
+        int page = addr >>> PAGE_SHIFT;
+        int entry = (addr >>> 2) & (PAGE_WORDS-1);
+        try {
+            return readPages[page][entry];
+        } catch(ArrayIndexOutOfBoundsException e) {
+            if(page < 0) throw e; // should never happen
+            if(page > readPages.length) throw new ReadFaultException(addr);
+            if(readPages[page] != emptyPage) throw e; // should never happen
+            initPage(page);
+            return 0;
+        } catch(NullPointerException e) {
+            throw new ReadFaultException(addr);
+        }
+    }
+    
+    protected final void memWrite(int addr, int value) throws WriteFaultException  {
+        if((addr & 3) != 0) throw new WriteFaultException(addr);
+        int page = addr >>> PAGE_SHIFT;
+        int entry = (addr>>>2)&(PAGE_WORDS-1);
+        try {
+            writePages[page][entry] = value;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            if(page < 0) throw e;// should never happen
+            if(page > writePages.length) throw new WriteFaultException(addr);
+            if(readPages[page] != emptyPage) throw e; // should never happen
+            initPage(page);
+            writePages[page][entry] = value;
+        } catch(NullPointerException e) {
+            throw new WriteFaultException(addr);
+        }
+    }
+    
+    protected void initPage(int page) { writePages[page] = readPages[page] = new int[PAGE_WORDS]; }
+    
+    public final int exitStatus() {
+        if(state != DONE) throw new IllegalStateException("exitStatus() called in an inappropriate state");
+        return exitStatus;
+    }
+     
+    public final int run(String[] args) throws EmulationException {
+        start(args);
+        for(;;) {
+            execute();
+            if(state != PAUSED) break;
+            System.err.println("WARNING: Pause requested while executing run()");
+            try { Thread.sleep(500); } catch(InterruptedException e) { }
+        }
+        if(state != DONE) throw new IllegalStateException("run() ended up in an inappropriate state");
+        return exitStatus();
+    }
+    
+    private void addArgs(String[] args) throws EmulationException {
+        if(state == UNINITIALIZED || state == RUNNING || state == PAUSED) throw new IllegalStateException("addArgs() called in inappropriate state");
+        int count = args.length;
+        byte[] nullTerminator = new byte[1];
+        int total = 4; /* null last table entry  */
+        for(int i=0;i<count;i++) total += args[i].length() + 1/*null terminator*/ + 4/*table entry*/;
+        if(total > PAGE_SIZE) throw new EmulationException("Arguments too large");
+        int start = ARGS_ADDR;
+        int addr = start + (count+1)*4;
+        int[] table = new int[count+1];
+        for(int i=0;i<count;i++) {
+            byte[] a;
+            try { a = args[i].getBytes("US-ASCII"); } catch(UnsupportedEncodingException e){ throw  new Error(e.getMessage()); }
+            table[i] = addr;
+
+                copyout(a,addr,a.length);
+                addr += a.length;
+                copyout(nullTerminator,addr,1);
+                addr += 1;
+
+        }
+        addr=start;
+        for(int i=0;i<count;i++) {
+            memWrite(addr,table[i]);
+            addr += 4;
+        }
+    }
+    
+    public void setUserInfo(int index, int word) throws EmulationException {
+        if(index < 0 ||  index >= 1024) throw new EmulationException("setUserInfo called with index >= 1024");
+        memWrite(USER_INFO_ADDR+index*4,word);
+    }
+    
+    public int getUserInfo(int index) throws EmulationException {
+        if(index < 0 ||  index >= 1024) throw new EmulationException("getUserInfo called with index >= 1024");
+        return memRead(USER_INFO_ADDR+index*4);
+    }
+    
+    public final void start(String[] args) throws EmulationException {
+        if(state == UNINITIALIZED || state == RUNNING || state == PAUSED) throw new IllegalStateException("start() called in inappropriate state");
+        _start(entryPoint);
+        addArgs(args);
+        fds = new FileDescriptor[OPEN_MAX];
+        fds[0] = new InputStreamFD(System.in)   { public boolean isatty() { return true; } };
+        fds[1] = new OutputStreamFD(System.out) { public boolean isatty() { return true; } };
+        fds[2] = new OutputStreamFD(System.err) { public boolean isatty() { return true; } };
+        state = PAUSED;
+    }
+    
+        
+    // Syscalls
+    private int write(int fdn, int addr, int count) {
+        int n = 0;
+        int r;
+        FileDescriptor fd;
+        count = Math.min(count,MAX_CHUNK);
+        try {
+            fd = fds[fdn];
+            if(fd == null || !fd.writable()) return -EBADFD;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            return -EBADFD;
+        }
+        try {
+            byte[] buf = byteBuf(count);
+            copyin(addr,buf,count);
+            return fd.write(buf,0,count);
+        } catch(FaultException e) {
+            System.err.println(e);
+            return -EFAULT;
+        } catch(IOException e) {
+            System.err.println(e);
+            return -EIO;
+        }
+    }
+
+    private int read(int fdn, int addr, int count) {
+        FileDescriptor fd;
+        count = Math.min(count,MAX_CHUNK);
+        try {
+            fd = fds[fdn];
+            if(fd == null || !fd.readable()) return -EBADFD;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            return -EBADFD;
+        }
+        try {
+            byte[] buf = byteBuf(count);
+            int n = fd.read(buf,0,count);
+            copyout(buf,addr,n);
+            return n;
+        } catch(FaultException e) {
+            System.err.println(e);
+            return -EFAULT;
+        } catch(IOException e) {
+            System.err.println(e);
+            return -EIO;
+        }
+    }
+    
+    private int close(int fdn) {
+        FileDescriptor fd;
+        try {
+            fd = fds[fdn];
+            if(fd == null) return -EBADFD;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            return -EBADFD;
+        }
+        fds[fdn] = null;
+        fd.close();
+        return 0;
+    }
+    
+    private int stat(FileInfo fi, int addr) {
+        int size = fi.size();
+        try {
+            memWrite(addr+0,0); // st_dev (top 16), // st_ino (bottom 16)
+            memWrite(addr+4,(fi.type() & 0xf000)|0644); // st_mode
+            memWrite(addr+8,1); // st_nlink (top 16) // st_uid (bottom 16)
+            memWrite(addr+12,0); // st_gid (top 16) // st_rdev (bottom 16)
+            memWrite(addr+16,size); // st_size
+            memWrite(addr+20,0); // st_atime
+            // memWrite(addr+24,0) // st_spare1
+            memWrite(addr+28,(int)(fi.modTime()/1000)); // st_mtime
+            // memWrite(addr+32,0) // st_spare2
+            memWrite(addr+36,0); // st_atime
+            // memWrite(addr+40,0) // st_spare3
+            memWrite(addr+44,512); // st_bklsize;
+            memWrite(addr+48,(size+511)&(~511)); // st_blocks
+            // memWrite(addr+52,0) // st_spare4[0]
+            // memWrite(addr+56,0) // st_spare4[1]
+        } catch(FaultException e) {
+            System.err.println(e);
+            return -EFAULT;
+        }
+        return 0;
+    }
+    
+    private int fstat(int fdn, int addr) {
+        FileDescriptor fd;
+        try {
+            fd = fds[fdn];
+            if(fd == null) return -EBADFD;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            return -EBADFD;
+        }
+        return stat(fd.fileInfo(),addr);
+    }
+    
+    public int sbrk(int incr) {
+        if(incr==0) return brk<<PAGE_SHIFT;
+        int oldBrk = brk;
+        int newBrk = oldBrk + ((incr+PAGE_SIZE-1)>>PAGE_SHIFT);
+        if(newBrk >= BRK_LIMIT) {
+            System.err.println("Hit BRK_LIMIT");
+            return -ENOMEM;
+        }
+        for(int i=oldBrk;i<newBrk+256;i++)
+            readPages[i] = writePages[i] = emptyPage;
+        brk = newBrk;
+        return oldBrk<<PAGE_SHIFT;
+    }
+        
+    private int open(int addr, int flags, int mode) {
+        final int O_RDONLY = 0;
+        final int O_WRONLY = 1;
+        final int O_RDWR = 2;
+        final int O_APPEND = 0x0008;
+        final int O_CREAT = 0x0200;
+        final int O_NONBLOCK = 0x4000;
+        final int O_EXCL = 0x0800;
+        
+        if((flags & O_APPEND) != 0) {
+            System.err.println("WARNING: O_APPEND not supported");
+            return -EOPNOTSUPP;
+        }
+        if((flags & O_NONBLOCK) != 0) {
+            System.err.println("WARNING: O_NONBLOCK not supported");
+            return -EOPNOTSUPP;
+        }
+        
+        try {
+            int fdn=-1;
+            File f = new File(cstring(addr));
+            System.err.println("Opening: " + f);
+            if((flags & O_EXCL) != 0 && (flags & O_CREAT) != 0)
+                if(!f.createNewFile()) return -EEXIST;
+            if(f.exists()) {
+                if(f.length() >= Integer.MAX_VALUE) return -EOPNOTSUPP;
+            } else {
+                if((flags & O_CREAT) == 0) return -ENOENT;
+            }
+            for(int i=0;i<OPEN_MAX;i++) if(fds[i] == null) { fdn = i; break; }
+            if(fdn==-1) return -ENFILE;
+            fds[fdn] = new RegularFileDescriptor(f,flags&3);
+            return fdn;
+        } catch(FaultException e) {
+            return -EFAULT;
+        } catch(FileNotFoundException e) { 
+            if(e.getMessage().indexOf("Permission denied") >= 0) return -EACCES;
+            return -ENOENT;
+        } catch(IOException e) {
+            return -EIO;
+        }
+    }
+    
+    private int seek(int fdn, int offset, int whence) {
+        FileDescriptor fd;
+        try {
+            fd = fds[fdn];
+            if(fd == null || !fd.readable()) return -EBADFD;
+        } catch(ArrayIndexOutOfBoundsException e) {
+            return -EBADFD;
+        }
+        try {
+            return fd.seek(offset,whence);
+        } catch(IOException e) {
+            System.err.println(e);
+            return -EPIPE;
+        }
+    }
+    
+    // This will only be called by raise() to invoke the default handler
+    // We don't have to worry about actually delivering the signal
+    private int kill(int pid, int signal) {
+        if(pid != PID) return -ESRCH;
+        if(signal < 0 || signal >= 32) return -EINVAL;
+        switch(signal) {
+            case 0: return 0;
+            case 17: // SIGSTOP
+            case 18: // SIGTSTP
+            case 21: // SIGTTIN
+            case 22: // SIGTTOU
+                state = PAUSED;
+                break;
+            case 19: // SIGCONT
+            case 20: // SIGCHLD
+            case 23: // SIGIO
+            case 28: // SIGWINCH
+                break;
+            default: {
+                String msg = "Terminating on signal: " + signal + "\n";
+                exitStatus = 1;
+                state = DONE;
+                if(fds[2]==null) {
+                    System.out.print(msg);
+                } else {
+                    byte[] b = msg.getBytes();
+                    try {
+                        fds[2].write(b,0,b.length);
+                    } catch(IOException e) { }
+                }
+            }
+        }
+        return 0;
+    }
+    
+    private int getpid() { return PID; }
+    
+    protected int syscall(int syscall, int a, int b, int c, int d) {
+        switch(syscall) {
+            case SYS_null: return 0;
+            case SYS_exit: exitStatus = a; state = DONE; return 0;
+            case SYS_pause: state = PAUSED; return 0;
+            case SYS_write: return write(a,b,c);
+            case SYS_fstat: return fstat(a,b);
+            case SYS_sbrk: return sbrk(a);
+            case SYS_open: return open(a,b,c);
+            case SYS_close: return close(a);
+            case SYS_read: return read(a,b,c);
+            case SYS_seek: return seek(a,b,c);
+            case SYS_kill: return kill(a,b);
+            case SYS_getpid: return getpid();
+            default:
+                System.err.println("Attempted to use unknown syscall: " + syscall);
+                return -ENOSYS;
+        }
+    }
+    
+    // Helper function to read a cstring from main memory
+    private String cstring(int addr) throws ReadFaultException {
+        StringBuffer sb = new StringBuffer();
+        for(;;) {
+            int word = memRead(addr&~3);
+            switch(addr&3) {
+                case 0: if(((word>>>24)&0xff)==0) return sb.toString(); sb.append((char)((word>>>24)&0xff)); addr++;
+                case 1: if(((word>>>16)&0xff)==0) return sb.toString(); sb.append((char)((word>>>16)&0xff)); addr++;
+                case 2: if(((word>>> 8)&0xff)==0) return sb.toString(); sb.append((char)((word>>> 8)&0xff)); addr++;
+                case 3: if(((word>>> 0)&0xff)==0) return sb.toString(); sb.append((char)((word>>> 0)&0xff)); addr++;
+            }
+        }
+    }
+     
+    // Exceptions
+    public static class ReadFaultException extends FaultException {
+        public ReadFaultException(int addr) { super(addr); }
+    }
+    public static class WriteFaultException extends FaultException {
+        public WriteFaultException(int addr) { super(addr); }
+    }
+    public static abstract class FaultException extends EmulationException {
+        private int addr;
+        public FaultException(int addr) { this.addr = addr; }
+        public String getMessage() { return "fault at: " + toHex(addr); }
+    }
+    public static class EmulationException extends Exception {
+        public EmulationException() { }
+        public EmulationException(String s) { super(s); }
+    }
+    
+    // FileInfo classes - used by stat(2)
+    static class FileInfo {
+        public static final int S_IFIFO = 0010000;
+        public static final int S_FCHR =  0020000;
+        public static final int S_IFDIR = 0040000;
+        public static final int S_IFREG = 0100000;
+        
+        public int size() { return 0; }
+        public int type() { return S_IFIFO; }
+        public long modTime() { return 0; }
+    }
+        
+    public static class FileFileInfo extends FileInfo {
+        public File f;
+        public FileFileInfo(File f) { this.f = f; }
+        public int size() { return (int)f.length(); }
+        public int type() { return f.isDirectory() ? S_IFDIR : S_IFREG; }
+        public long modTime() { return f.lastModified(); }
+    }
+
+    // File descriptor classes
+    public static abstract class FileDescriptor {
+        public boolean readable() { return false; }
+        public boolean writable() { return false; }
+        
+        private static final FileInfo nullFi = new FileInfo();
+        private FileInfo fi;
+        public FileInfo fileInfo() { return fi; }
+        
+        FileDescriptor() { this(null); }
+        FileDescriptor(FileInfo fi) { this.fi = fi==null ? nullFi : fi; }
+        
+        public int read(byte[] a, int off, int length) throws IOException { throw new IOException("no definition"); }
+        public int write(byte[] a, int off, int length) throws IOException { throw new IOException("no definition"); }
+        
+        public int seek(int n, int whence)  throws IOException  { return -ESPIPE; }
+        public boolean isatty() { return false; }
+        
+        void close() { }
+    }
+    
+    public static class RegularFileDescriptor extends FileDescriptor {
+        private int mode;
+        private RandomAccessFile raf;
+        public boolean readable() { return mode != 1; }
+        public boolean writable() { return mode != 0; }
+        
+        RegularFileDescriptor(File f,int m) throws IOException {
+            super(new FileFileInfo(f));
+            String mode = m == 0 ? "r" : "rw";
+            this.mode = m;
+            raf = new RandomAccessFile(f,mode);
+            if(raf.length() >= Integer.MAX_VALUE) throw new IOException("File too large");
+        }
+        
+        public int seek(int n, int whence) throws IOException {
+            final int SEEK_SET = 0;
+            final int SEEK_CUR = 1;
+            final int SEEK_END = 2;
+            
+            switch(whence) {
+                case SEEK_SET: break;
+                case SEEK_CUR: n = (int)(raf.getFilePointer()+n); break;
+                case SEEK_END: n = (int)(raf.length()+n); break;
+                default: return -EINVAL;
+            }
+            raf.seek(n);
+            return n;
+        }
+        
+        public int write(byte[] a, int off, int length) throws IOException { raf.write(a,off,length); return length; }
+        public int read(byte[] a, int off, int length) throws IOException { int n = raf.read(a,off,length); return n < 0 ? 0 : n; }
+        
+        void close() { try { raf.close(); } catch(Exception e) { } }
+    }
+    
+    public class OutputStreamFD extends FileDescriptor {
+        private OutputStream os;
+        public boolean writable() { return true; }
+        public OutputStreamFD(OutputStream os) { this.os = os; }
+        public int write(byte[] a, int off, int length) throws IOException { os.write(a,off,length); return length; }
+    }
+    
+    public class InputStreamFD extends FileDescriptor {
+        private InputStream is;
+        public boolean readable() { return true; }
+        public InputStreamFD(InputStream is) { this.is = is; }
+        public int read(byte[] a, int off, int length) throws IOException { int n = is.read(a,off,length); return n < 0 ? 0 : n; }
+    }
+    
+    // Utility functions
+    private byte[] byteBuf(int size) {
+        if(_byteBuf==null) _byteBuf = new byte[size];
+        else if(_byteBuf.length < size)
+            _byteBuf = new byte[min(max(_byteBuf.length*2,size),MAX_CHUNK+8)];
+        return _byteBuf;
+    }
+    protected final static String toHex(int n) { return "0x" + Long.toString(n & 0xffffffffL, 16); }
+    protected final static int min(int a, int b) { return a < b ? a : b; }
+    protected final static int max(int a, int b) { return a > b ? a : b; }
+}
+
+class ELF {
+    private MyRandomAccessFile fd;
+    
+    public ELFHeader header;
+    public PHeader[] pheaders;
+    public SHeader[] sheaders;
+    
+    private boolean sectionReaderActive;
+    
+    public class ELFHeader {
+        byte klass;
+        byte data;
+        byte osabi;
+        byte abiversion;
+        
+        public static final short ET_EXEC = 2;
+        public short type;
+        public static final short EM_MIPS = 8;
+        public short machine;
+        public int version;
+        public int entry;
+        public int phoff;
+        public int shoff;
+        public int flags;
+        public short ehsize;
+        public short phentsize;
+        public short phnum;
+        public short shentsize;
+        public short shnum;
+        public short shstrndx;
+
+        private static final int ELF_MAGIC = 0x7f454c46; // '\177', 'E', 'L', 'F'
+        ELFHeader() throws IOException {
+            if(fd.readInt() != ELF_MAGIC) throw new ELFException("Bad Magic (is: " );
+            klass = fd.readByte();
+            data = fd.readByte();
+            fd.skipFully(1); // version
+            osabi = fd.readByte();
+            abiversion = fd.readByte();
+            fd.skipFully(7);
+            type = fd.readShort();
+            machine = fd.readShort();
+            version = fd.readInt();
+            entry = fd.readInt();
+            phoff = fd.readInt();
+            shoff = fd.readInt();
+            flags = fd.readInt();
+            ehsize = fd.readShort();
+            phentsize = fd.readShort();
+            phnum = fd.readShort();
+            shentsize = fd.readShort();
+            shnum = fd.readShort();
+            shstrndx = fd.readShort();
+        }
+    }
+    
+    public class PHeader {
+        public int type;
+        public int offset;
+        public int vaddr;
+        public int paddr;
+        public int filesz;
+        public int memsz;
+        public int flags;
+        public int align;
+        
+        public static final int PF_X = 0x1;
+        public static final int PF_W = 0x2;
+        public static final int PF_R = 0x4;
+        
+        public static final int PT_LOAD = 1;
+        
+        PHeader() throws IOException {
+            type = fd.readInt();
+            offset = fd.readInt();
+            vaddr = fd.readInt();
+            paddr = fd.readInt();
+            filesz = fd.readInt();
+            memsz = fd.readInt();
+            flags = fd.readInt();
+            align = fd.readInt();
+            if(filesz > memsz) throw new ELFException("ELF inconsistency: filesz > memsz");
+        }
+        
+        public boolean writable() { return (flags & PF_W) != 0; }
+        
+        public InputStream getInputStream() throws IOException {
+            return new BufferedInputStream(new SectionInputStream(
+                offset,offset+filesz));
+        }
+    }
+    
+    public class SHeader {
+        int nameidx;
+        public String name;
+        public int type;
+        public int flags;
+        public int addr;
+        public int offset;
+        public int size;
+        public int link;
+        public int info;
+        public int addralign;
+        public int entsize;
+        
+        public static final int T_NOBITS = 8;
+        
+        SHeader() throws IOException {
+            nameidx = fd.readInt();
+            type = fd.readInt();
+            flags = fd.readInt();
+            addr = fd.readInt();
+            offset = fd.readInt();
+            size = fd.readInt();
+            link = fd.readInt();
+            info = fd.readInt();
+            addralign = fd.readInt();
+            entsize = fd.readInt();
+        }
+        
+        public InputStream getInputStream() throws IOException {
+            return new BufferedInputStream(new SectionInputStream(
+                offset, type == T_NOBITS ? 0 : offset+size));
+        }
+    }
+    
+    public ELF(String file) throws IOException, ELFException {
+        fd = new MyRandomAccessFile(file,"r");
+        header = new ELFHeader();
+        pheaders = new PHeader[header.phnum];
+        for(int i=0;i<header.phnum;i++) {
+            fd.seek(header.phoff+i*header.phentsize);
+            pheaders[i] = new PHeader();
+        }
+        sheaders = new SHeader[header.shnum];
+        for(int i=0;i<header.shnum;i++) {
+            fd.seek(header.shoff+i*header.shentsize);
+            sheaders[i] = new SHeader();
+        }
+        if(header.shstrndx < 0 || header.shstrndx >= header.shnum) throw new ELFException("Bad shstrndx");
+        fd.seek(sheaders[header.shstrndx].offset);
+        byte[] a = new byte[sheaders[header.shstrndx].size];
+        fd.readFully(a);
+        for(int i=0;i<header.shnum;i++) {
+            SHeader s = sheaders[i];
+            StringBuffer sb = new StringBuffer();
+               for(int off = s.nameidx;off < a.length && a[off] != 0; off++) sb.append((char)a[off]);
+            s.name = sb.toString();
+        }            
+    }
+        
+    public SHeader sectionWithName(String name) {
+        for(int i=0;i<sheaders.length;i++)
+            if(sheaders[i].name.equals(name))
+                return sheaders[i];
+        return null;
+    }
+    
+    public class ELFException extends IOException { ELFException(String s) { super(s); } }
+    
+    private class MyRandomAccessFile extends RandomAccessFile  {
+        MyRandomAccessFile(String f,String m) throws IOException { super(f,m); }
+        public void skipFully(int n) throws IOException {
+            while(n>0) n-= skipBytes(n);
+        }
+    }
+
+    private class SectionInputStream extends InputStream {
+        private int pos;
+        private int maxpos;
+        SectionInputStream(int start, int end) throws IOException {
+            if(sectionReaderActive)
+                throw new IOException("Section reader already active");
+            sectionReaderActive = true;
+            pos = start;
+            fd.seek(pos);
+            maxpos = end;
+        }
+        
+        private int bytesLeft() { return maxpos - pos; }
+        public int read() throws IOException { if(bytesLeft()==0) return -1; int b = fd.read(); if(b >= 0) pos++; return b; }
+        public int read(byte[] b, int off, int len) throws IOException {
+            int n = fd.read(b,off,Math.min(len,bytesLeft())); if(n > 0) pos += n; return n;
+        }
+        public void close() { sectionReaderActive = false; }
+    }
+    
+    private static String toHex(int n) { return "0x" + Long.toString(n & 0xffffffffL, 16); }
+    
+    public static void main(String[] args) throws IOException {
+        ELF elf = new ELF(args[0]);
+        System.out.println("Type: " + toHex(elf.header.type));
+        System.out.println("Machine: " + toHex(elf.header.machine));
+        for(int i=0;i<elf.pheaders.length;i++) {
+            ELF.PHeader ph = elf.pheaders[i];
+            System.out.println("PHeader " + toHex(i));
+            System.out.println("\tOffset: " + ph.offset);
+            System.out.println("\tVaddr: " + toHex(ph.vaddr));
+            System.out.println("\tFile Size: " + ph.filesz);
+            System.out.println("\tMem Size: " + ph.memsz);
+        }
+        for(int i=0;i<elf.sheaders.length;i++) {
+            ELF.SHeader sh = elf.sheaders[i];
+            System.out.println("SHeader " + toHex(i));
+            System.out.println("\tName: " + sh.name);
+            System.out.println("\tOffset: " + sh.offset);
+            System.out.println("\tAddr: " + toHex(sh.addr));
+            System.out.println("\tSize: " + sh.size);
+            System.out.println("\tType: " + toHex(sh.type));
+        }
+    }
+}
+interface Errno {
+    public static final int EPERM = 1;
+    public static final int ENOENT = 2;
+    public static final int ESRCH = 3;
+    public static final int EINTR = 4;
+    public static final int EIO = 5;
+    public static final int ENXIO = 6;
+    public static final int ENOEXEC = 8;
+    public static final int EBADF = 9;
+    public static final int ECHILD = 10;
+    public static final int EAGAIN = 11;
+    public static final int ENOMEM = 12;
+    public static final int EACCES = 13;
+    public static final int EFAULT = 14;
+    public static final int ENOTBLK = 15;
+    public static final int EBUSY = 16;
+    public static final int EEXIST = 17;
+    public static final int EXDEV = 18;
+    public static final int ENODEV = 19;
+    public static final int ENOTDIR = 20;
+    public static final int EISDIR = 21;
+    public static final int EINVAL = 22;
+    public static final int ENFILE = 23;
+    public static final int EMFILE = 24;
+    public static final int ENOTTY = 25;
+    public static final int ETXTBSY = 26;
+    public static final int EFBIG = 27;
+    public static final int ENOSPC = 28;
+    public static final int ESPIPE = 29;
+    public static final int EROFS = 30;
+    public static final int EMLINK = 31;
+    public static final int EPIPE = 32;
+    public static final int EDOM = 33;
+    public static final int ERANGE = 34;
+    public static final int ENOMSG = 35;
+    public static final int EIDRM = 36;
+    public static final int ECHRNG = 37;
+    public static final int ELNRNG = 41;
+    public static final int EUNATCH = 42;
+    public static final int ENOCSI = 43;
+    public static final int EDEADLK = 45;
+    public static final int ENOLCK = 46;
+    public static final int EBADE = 50;
+    public static final int EBADR = 51;
+    public static final int EXFULL = 52;
+    public static final int ENOANO = 53;
+    public static final int EBADRQC = 54;
+    public static final int EBADSLT = 55;
+    public static final int EDEADLOCK = 56;
+    public static final int EBFONT = 57;
+    public static final int ENOSTR = 60;
+    public static final int ENODATA = 61;
+    public static final int ETIME = 62;
+    public static final int ENOSR = 63;
+    public static final int ENONET = 64;
+    public static final int ENOPKG = 65;
+    public static final int EREMOTE = 66;
+    public static final int ENOLINK = 67;
+    public static final int EADV = 68;
+    public static final int ESRMNT = 69;
+    public static final int ECOMM = 70;
+    public static final int EPROTO = 71;
+    public static final int EMULTIHOP = 74;
+    public static final int ELBIN = 75;
+    public static final int EDOTDOT = 76;
+    public static final int EBADMSG = 77;
+    public static final int EFTYPE = 79;
+    public static final int ENOTUNIQ = 80;
+    public static final int EBADFD = 81;
+    public static final int EREMCHG = 82;
+    public static final int ELIBACC = 83;
+    public static final int ELIBBAD = 84;
+    public static final int ELIBSCN = 85;
+    public static final int ELIBMAX = 86;
+    public static final int ELIBEXEC = 87;
+    public static final int ENOSYS = 88;
+    public static final int ENMFILE = 89;
+    public static final int ENOTEMPTY = 90;
+    public static final int ENAMETOOLONG = 91;
+    public static final int ELOOP = 92;
+    public static final int EOPNOTSUPP = 95;
+    public static final int EPFNOSUPPORT = 96;
+    public static final int ECONNRESET = 104;
+    public static final int ENOBUFS = 105;
+    public static final int EAFNOSUPPORT = 106;
+    public static final int EPROTOTYPE = 107;
+    public static final int ENOTSOCK = 108;
+    public static final int ENOPROTOOPT = 109;
+    public static final int ESHUTDOWN = 110;
+    public static final int ECONNREFUSED = 111;
+    public static final int EADDRINUSE = 112;
+    public static final int ECONNABORTED = 113;
+    public static final int ENETUNREACH = 114;
+    public static final int ENETDOWN = 115;
+    public static final int ETIMEDOUT = 116;
+    public static final int EHOSTDOWN = 117;
+    public static final int EHOSTUNREACH = 118;
+    public static final int EINPROGRESS = 119;
+    public static final int EALREADY = 120;
+    public static final int EDESTADDRREQ = 121;
+    public static final int EMSGSIZE = 122;
+    public static final int EPROTONOSUPPORT = 123;
+    public static final int ESOCKTNOSUPPORT = 124;
+    public static final int EADDRNOTAVAIL = 125;
+    public static final int ENETRESET = 126;
+    public static final int EISCONN = 127;
+    public static final int ENOTCONN = 128;
+    public static final int ETOOMANYREFS = 129;
+    public static final int EPROCLIM = 130;
+    public static final int EUSERS = 131;
+    public static final int EDQUOT = 132;
+    public static final int ESTALE = 133;
+    public static final int ENOTSUP = 134;
+    public static final int ENOMEDIUM = 135;
+    public static final int ENOSHARE = 136;
+    public static final int ECASECLASH = 137;
+    public static final int EILSEQ = 138;
+    public static final int EOVERFLOW = 139;
+    public static final int __ELASTERROR = 2000;
+}
+interface Syscalls {
+    public static final int SYS_null = 0;
+    public static final int SYS_exit = 1;
+    public static final int SYS_pause = 2;
+    public static final int SYS_open = 3;
+    public static final int SYS_close = 4;
+    public static final int SYS_read = 5;
+    public static final int SYS_write = 6;
+    public static final int SYS_sbrk = 7;
+    public static final int SYS_fstat = 8;
+    public static final int SYS_isatty = 9;
+    public static final int SYS_seek = 10;
+    public static final int SYS_kill = 11;
+    public static final int SYS_getpid = 12;
+}