Get the ARM simulator to throw an exception on unaligned accesses.

src/simulator-arm.cc

 // Copyright 2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 410 matching lines @@
   registers_[pc] = value;
 }
 
 
 // Raw access to the PC register without the special adjustment when reading.
 int32_t Simulator::get_pc() const {
   return registers_[pc];
 }
 
 
+// The ARM cannot do unaligned reads and writes.  On some ARM platforms an
+// interrupt is caused.  On others it does a funky rotation thing.  For now we
+// simply disallow unaligned reads, but at some point we may want to move to
+// emulating the rotate behaviour.  Note that simulator runs have the runtime
+// system running directly on the host system and only generated code is
+// executed in the simulator.  Since the host is typically IA32 we will not
+// get the correct ARM-like behaviour on unaligned accesses.
+
+int Simulator::ReadW(int32_t addr) {
+  if ((addr & 3) == 0) {
+    intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
+    return *ptr;
+  }
+  PrintF("Unaligned read at %x\n", addr);

[iposva, 2008/10/28 15:34:17]

It would be helpful to print the PC and the address in the failure messages such
as:
"Unaligned read from %x at %x\n"

+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+void Simulator::WriteW(int32_t addr, int value) {
+  if ((addr & 3) == 0) {
+    intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
+    *ptr = value;
+    return;
+  }
+  PrintF("Unaligned write at %x\n", addr);
+  UNIMPLEMENTED();
+}
+
+
+uint16_t Simulator::ReadHU(int32_t addr) {
+  if ((addr & 1) == 0) {
+    uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
+    return *ptr;
+  }
+  PrintF("Unaligned read at %x\n", addr);
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+int16_t Simulator::ReadH(int32_t addr) {
+  if ((addr & 1) == 0) {
+    int16_t* ptr = reinterpret_cast<int16_t*>(addr);
+    return *ptr;
+  }
+  PrintF("Unaligned read at %x\n", addr);
+  UNIMPLEMENTED();
+  return 0;
+}
+
+
+void Simulator::WriteH(int32_t addr, uint16_t value) {

[iposva, 2008/10/28 15:34:17]

The two WriteH and WriteB variants are really hard to distinguish, but I do not
have a better suggestion for you either.
Maybe a comment would help?

+  if ((addr & 1) == 0) {
+    uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
+    *ptr = value;
+    return;
+  }
+  PrintF("Unaligned write at %x\n", addr);
+  UNIMPLEMENTED();
+}
+
+
+void Simulator::WriteH(int32_t addr, int16_t value) {
+  if ((addr & 1) == 0) {
+    int16_t* ptr = reinterpret_cast<int16_t*>(addr);
+    *ptr = value;
+    return;
+  }
+  PrintF("Unaligned write at %x\n", addr);
+  UNIMPLEMENTED();
+}
+
+
+uint8_t Simulator::ReadBU(int32_t addr) {
+  uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);

[iposva, 2008/10/28 15:34:17]

Why no alignment check here? ;-)

+  return *ptr;
+}
+
+
+int8_t Simulator::ReadB(int32_t addr) {
+  int8_t* ptr = reinterpret_cast<int8_t*>(addr);
+  return *ptr;
+}
+
+
+void Simulator::WriteB(int32_t addr, uint8_t value) {
+  uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);
+  *ptr = value;
+}
+
+
+void Simulator::WriteB(int32_t addr, int8_t value) {
+  int8_t* ptr = reinterpret_cast<int8_t*>(addr);
+  *ptr = value;
+}
+
+
 // Returns the limit of the stack area to enable checking for stack overflows.
 uintptr_t Simulator::StackLimit() const {
   // Leave a safety margin of 256 bytes to prevent overrunning the stack when
   // pushing values.
   return reinterpret_cast<uintptr_t>(stack_) + 256;
 }
 
 
 // Unsupported instructions use Format to print an error and stop execution.
 void Simulator::Format(Instr* instr, const char* format) {
@@ skipping 505 matching lines @@
           }
           default: {
             // The PU field is a 2-bit field.
             UNREACHABLE();
             break;
           }
         }
       }
       if (instr->HasH()) {
         if (instr->HasSign()) {
-          int16_t* haddr = reinterpret_cast<int16_t*>(addr);
           if (instr->HasL()) {
-            int16_t val = *haddr;
+            int16_t val = ReadH(addr);
             set_register(rd, val);
           } else {
             int16_t val = get_register(rd);
-            *haddr = val;
+            WriteH(addr, val);
           }
         } else {
-          uint16_t* haddr = reinterpret_cast<uint16_t*>(addr);
           if (instr->HasL()) {
-            uint16_t val = *haddr;
+            uint16_t val = ReadHU(addr);
             set_register(rd, val);
           } else {
             uint16_t val = get_register(rd);
-            *haddr = val;
+            WriteH(addr, val);
           }
         }
       } else {
         // signed byte loads
         ASSERT(instr->HasSign());
         ASSERT(instr->HasL());
-        int8_t* baddr = reinterpret_cast<int8_t*>(addr);
-        int8_t val = *baddr;
+        int8_t val = ReadB(addr);
         set_register(rd, val);
       }
       return;
     }
   } else {
     int rd = instr->RdField();
     int rn = instr->RnField();
     int32_t rn_val = get_register(rn);
     int32_t shifter_operand = 0;
     bool shifter_carry_out = 0;
@@ skipping 234 matching lines @@
         set_register(rn, rn_val);
       }
       break;
     }
     default: {
       UNREACHABLE();
       break;
     }
   }
   if (instr->HasB()) {
-    byte* baddr = reinterpret_cast<byte*>(addr);
     if (instr->HasL()) {
-      byte val = *baddr;
+      byte val = ReadBU(addr);
       set_register(rd, val);
     } else {
       byte val = get_register(rd);
-      *baddr = val;
+      WriteB(addr, val);
     }
   } else {
-    intptr_t* iaddr = reinterpret_cast<intptr_t*>(addr);
     if (instr->HasL()) {
-      set_register(rd, *iaddr);
+      set_register(rd, ReadW(addr));
     } else {
-      *iaddr = get_register(rd);
+      WriteW(addr, get_register(rd));
     }
   }
 }
 
 
 void Simulator::DecodeType3(Instr* instr) {
   int rd = instr->RdField();
   int rn = instr->RnField();
   int32_t rn_val = get_register(rn);
   bool shifter_carry_out = 0;
@@ skipping 27 matching lines @@
       break;
     }
     default: {
       UNREACHABLE();
       break;
     }
   }
   if (instr->HasB()) {
     UNIMPLEMENTED();
   } else {
-    intptr_t* iaddr = reinterpret_cast<intptr_t*>(addr);
     if (instr->HasL()) {
-      set_register(rd, *iaddr);
+      set_register(rd, ReadW(addr));
     } else {
-      *iaddr = get_register(rd);
+      WriteW(addr, get_register(rd));
     }
   }
 }
 
 
 void Simulator::DecodeType4(Instr* instr) {
   ASSERT(instr->Bit(22) == 0);  // only allowed to be set in privileged mode
   if (instr->HasL()) {
     // Format(instr, "ldm'cond'pu 'rn'w, 'rlist");
     HandleRList(instr, true);
@@ skipping 187 matching lines @@
   set_register(r10, r10_val);
   set_register(r11, r11_val);
 
   int result = get_register(r0);
   return reinterpret_cast<Object*>(result);
 }
 
 } }  // namespace assembler::arm
 
 #endif  // !defined(__arm__)