2 files changed, 29 insertions, 8 deletions

diff --git a/src/arch/arm/predecoder.cc b/src/arch/arm/predecoder.cc
index 456b9e4c4..71d399e35 100644
--- a/src/arch/arm/predecoder.cc
+++ b/src/arch/arm/predecoder.cc
@@ -74,11 +74,15 @@ Predecoder::advanceThumbCond()
 void
 Predecoder::process()
 {
+    // emi is typically ready, with some caveats below...
+    emiReady = true;
+
     if (!emi.thumb) {
         emi.instBits = data;
         emi.sevenAndFour = bits(data, 7) && bits(data, 4);
         emi.isMisc = (bits(data, 24, 23) == 0x2 &&
                       bits(data, 20) == 0);
+        consumeBytes(4);
         DPRINTF(Predecoder, "Arm inst: %#x.\n", (uint64_t)emi);
     } else {
         uint16_t word = (data >> (offset * 8));
@@ -86,7 +90,7 @@ Predecoder::process()
             // A 32 bit thumb inst is half collected.
             emi.instBits = emi.instBits | word;
             bigThumb = false;
-            offset += 2;
+            consumeBytes(2);
             DPRINTF(Predecoder, "Second half of 32 bit Thumb: %#x.\n",
                     emi.instBits);
             if (itstate.mask) {
@@ -105,7 +109,7 @@ Predecoder::process()
                     emi.instBits = (data >> 16) | (data << 16);
                     DPRINTF(Predecoder, "All of 32 bit Thumb: %#x.\n",
                             emi.instBits);
-                    offset += 4;
+                    consumeBytes(4);
                     if (itstate.mask) {
                         emi.itstate = itstate;
                         advanceThumbCond();
@@ -117,11 +121,13 @@ Predecoder::process()
                             "First half of 32 bit Thumb.\n");
                     emi.instBits = (uint32_t)word << 16;
                     bigThumb = true;
-                    offset += 2;
+                    consumeBytes(2);
+                    // emi not ready yet.
+                    emiReady = false;
                 }
             } else {
                 // A 16 bit thumb inst.
-                offset += 2;
+                consumeBytes(2);
                 emi.instBits = word;
                 // Set the condition code field artificially.
                 emi.condCode = COND_UC;
@@ -159,6 +165,7 @@ Predecoder::moreBytes(const PCState &pc, Addr fetchPC, MachInst inst)
     CPSR cpsr = tc->readMiscReg(MISCREG_CPSR);
     itstate.top6 = cpsr.it2;
     itstate.bottom2 = cpsr.it1;
+    outOfBytes = false;
     process();
 }
 
diff --git a/src/arch/arm/predecoder.hh b/src/arch/arm/predecoder.hh
index 47242b8ff..92aab6e30 100644
--- a/src/arch/arm/predecoder.hh
+++ b/src/arch/arm/predecoder.hh
@@ -45,6 +45,8 @@
 #ifndef __ARCH_ARM_PREDECODER_HH__
 #define __ARCH_ARM_PREDECODER_HH__
 
+#include <cassert>
+
 #include "arch/arm/types.hh"
 #include "arch/arm/miscregs.hh"
 #include "base/types.hh"
@@ -61,6 +63,8 @@ namespace ArmISA
         ExtMachInst emi;
         MachInst data;
         bool bigThumb;
+        bool emiReady;
+        bool outOfBytes;
         int offset;
         ITSTATE itstate;
 
@@ -70,6 +74,8 @@ namespace ArmISA
             bigThumb = false;
             offset = 0;
             emi = 0;
+            emiReady = false;
+            outOfBytes = true;
         }
 
         Predecoder(ThreadContext * _tc) :
@@ -103,16 +109,22 @@ namespace ArmISA
             moreBytes(0, 0, machInst);
         }
 
+        inline void consumeBytes(int numBytes)
+        {
+            offset += numBytes;
+            assert(offset <= sizeof(MachInst));
+            if (offset == sizeof(MachInst))
+                outOfBytes = true;
+        }
+
         bool needMoreBytes()
         {
-            return sizeof(MachInst) > offset;
+            return outOfBytes;
         }
 
         bool extMachInstReady()
         {
-            // The only way an instruction wouldn't be ready is if this is a
-            // 32 bit ARM instruction that's not 32 bit aligned.
-            return !bigThumb;
+            return emiReady;
         }
 
         int getInstSize()
@@ -123,9 +135,11 @@ namespace ArmISA
         //This returns a constant reference to the ExtMachInst to avoid a copy
         ExtMachInst getExtMachInst(PCState &pc)
         {
+            assert(emiReady);
             ExtMachInst thisEmi = emi;
             pc.npc(pc.pc() + getInstSize());
             emi = 0;
+            emiReady = false;
             return thisEmi;
         }
     };