unaligned memory access support for ARMv7

src/arm/simulator-arm.cc

 // Copyright 2010 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 848 matching lines @@
 }
 
 
 void Simulator::TrashCallerSaveRegisters() {
   // We don't trash the registers with the return value.
   registers_[2] = 0x50Bad4U;
   registers_[3] = 0x50Bad4U;
   registers_[12] = 0x50Bad4U;
 }
 
-
-// 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
+// Some Operating Systems allow unaligned access on ARMv7 targets. We
+// assume that unaligned accesses are not allowed unless the v8 build system
+// defines the CAN_USE_UNALIGNED_ACCESSES macro to be non-zero.
+// The following statements below describes the behavior of the ARM CPUs
+// that don't support unaligned access.
+// Some ARM platforms raises an interrupt on detecting unaligned access.
+// 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.
+// get the correct ARM-like behaviour on unaligned accesses for those ARM
+// targets that don't support unaligned loads and stores.
+
 
 int Simulator::ReadW(int32_t addr, Instr* instr) {
+#if V8_TARGET_CAN_READ_UNALIGNED
+  intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
+  return *ptr;
+#else
   if ((addr & 3) == 0) {
     intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
     return *ptr;
   }
   PrintF("Unaligned read at 0x%08x\n", addr);
   UNIMPLEMENTED();
   return 0;
+#endif
 }
 
 
 void Simulator::WriteW(int32_t addr, int value, Instr* instr) {
+#if V8_TARGET_CAN_READ_UNALIGNED
+  intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
+  *ptr = value;
+  return;
+#else
   if ((addr & 3) == 0) {
     intptr_t* ptr = reinterpret_cast<intptr_t*>(addr);
     *ptr = value;
     return;
   }
   PrintF("Unaligned write at 0x%08x, pc=%p\n", addr, instr);
   UNIMPLEMENTED();
+#endif
 }
 
 
 uint16_t Simulator::ReadHU(int32_t addr, Instr* instr) {
+#if V8_TARGET_CAN_READ_UNALIGNED
+  uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
+  return *ptr;
+#else
   if ((addr & 1) == 0) {
     uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
     return *ptr;
   }
   PrintF("Unaligned unsigned halfword read at 0x%08x, pc=%p\n", addr, instr);
   UNIMPLEMENTED();
   return 0;
+#endif
 }
 
 
 int16_t Simulator::ReadH(int32_t addr, Instr* instr) {
+#if V8_TARGET_CAN_READ_UNALIGNED
+  int16_t* ptr = reinterpret_cast<int16_t*>(addr);
+  return *ptr;
+#else
   if ((addr & 1) == 0) {
     int16_t* ptr = reinterpret_cast<int16_t*>(addr);
     return *ptr;
   }
   PrintF("Unaligned signed halfword read at 0x%08x\n", addr);
   UNIMPLEMENTED();
   return 0;
+#endif
 }
 
 
 void Simulator::WriteH(int32_t addr, uint16_t value, Instr* instr) {
+#if V8_TARGET_CAN_READ_UNALIGNED
+  uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
+  *ptr = value;
+  return;
+#else
   if ((addr & 1) == 0) {
     uint16_t* ptr = reinterpret_cast<uint16_t*>(addr);
     *ptr = value;
     return;
   }
   PrintF("Unaligned unsigned halfword write at 0x%08x, pc=%p\n", addr, instr);
   UNIMPLEMENTED();
+#endif
 }
 
 
 void Simulator::WriteH(int32_t addr, int16_t value, Instr* instr) {
+#if V8_TARGET_CAN_READ_UNALIGNED
+  int16_t* ptr = reinterpret_cast<int16_t*>(addr);
+  *ptr = value;
+  return;
+#else
   if ((addr & 1) == 0) {
     int16_t* ptr = reinterpret_cast<int16_t*>(addr);
     *ptr = value;
     return;
   }
   PrintF("Unaligned halfword write at 0x%08x, pc=%p\n", addr, instr);
   UNIMPLEMENTED();
+#endif
 }
 
 
 uint8_t Simulator::ReadBU(int32_t addr) {
   uint8_t* ptr = reinterpret_cast<uint8_t*>(addr);
   return *ptr;
 }
 
 
 int8_t Simulator::ReadB(int32_t addr) {
@@ skipping 1681 matching lines @@
   int current_sp = get_register(sp);
   uintptr_t* stack_slot = reinterpret_cast<uintptr_t*>(current_sp);
   uintptr_t address = *stack_slot;
   set_register(sp, current_sp + sizeof(uintptr_t));
   return address;
 }
 
 } }  // namespace assembler::arm
 
 #endif  // __arm__