Deletion barrier: Distinguish+verify field initialization in ia32 generated code.

runtime/vm/assembler_ia32.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // NOLINT
 #if defined(TARGET_ARCH_IA32)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/cpu.h"
@@ skipping 1439 matching lines @@
     EmitUint8(0xA9);
     EmitImmediate(immediate);
   } else {
     EmitUint8(0xF7);
     EmitOperand(0, Operand(reg));
     EmitImmediate(immediate);
   }
 }
 
 
+void Assembler::testb(const Address& address, const Immediate& imm) {
+  ASSERT(imm.is_int8());
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0xF6);
+  EmitOperand(0, address);
+  EmitUint8(imm.value() & 0xFF);
+}
+
+
 void Assembler::andl(Register dst, Register src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x23);
   EmitOperand(dst, Operand(src));
 }
 
 
 void Assembler::andl(Register dst, const Immediate& imm) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitComplex(4, Operand(dst), imm);
@@ skipping 735 matching lines @@
   // Mask out higher, uninteresting bits which were polluted by dest.
   andl(value, Immediate(kObjectAlignment - 1));
   // Compare with the expected bit pattern.
   cmpl(value, Immediate(
       (kNewObjectAlignmentOffset >> 1) + kHeapObjectTag +
       kOldObjectAlignmentOffset + kHeapObjectTag));
   j(NOT_ZERO, no_update, Assembler::kNearJump);
 }
 
 
-void Assembler::VerifyHeapWord(const Address& address) {
+void Assembler::VerifyHeapWord(const Address& address,
+                               FieldContent old_content) {
+#if defined(DEBUG)
+  switch (old_content) {
+    case kEmptySmiOrNull:
+      VerifyUninitialized(address);
+      break;
+    case kHeapObjectOrSmi:
+      VerifyObjectOrSmi(address);
+      break;
+    case kOnlySmi:
+      VerifySmi(address);
+      break;
+  }
+#endif  // DEBUG
   if (VerifiedMemory::enabled()) {
     Register addr_reg = EDX;
     Register value = EBX;
     // Preserve registers.
     pushl(addr_reg);
     pushl(value);
     leal(addr_reg, address);
     // ASSERT(*address == *(address + offset))
     movl(value, Address(addr_reg, 0));
     cmpl(value, Address(addr_reg, VerifiedMemory::offset()));
     Label ok;
     j(EQUAL, &ok, Assembler::kNearJump);
     Stop("Write barrier verification failed");
     Bind(&ok);
     popl(value);
     popl(addr_reg);
   }
 }
 
 
-void Assembler::VerifiedWrite(const Address& dest, Register value) {
-  VerifyHeapWord(dest);
+void Assembler::VerifiedWrite(const Address& dest,
+                              Register value,
+                              FieldContent old_content) {
+  VerifyHeapWord(dest, old_content);
   movl(dest, value);
   if (VerifiedMemory::enabled()) {
     Register temp = (value == EDX) ? ECX : EDX;
     pushl(temp);
     leal(temp, dest);
     movl(Address(temp, VerifiedMemory::offset()), value);
     popl(temp);
   }
 }
 
 
+#if defined(DEBUG)
+void Assembler::VerifyObjectOrSmi(const Address& dest) {
+  Label ok;
+  testb(dest, Immediate(kHeapObjectTag));
+  j(ZERO, &ok, Assembler::kNearJump);
+  // Non-smi case: Verify object pointer is word-aligned when untagged.
+  COMPILE_ASSERT(kHeapObjectTag == 1);
+  testb(dest, Immediate((kWordSize - 1) - kHeapObjectTag));
+  j(ZERO, &ok, Assembler::kNearJump);
+  Stop("Expected heap object or Smi");
+  Bind(&ok);
+}
+
+
+void Assembler::VerifyUninitialized(const Address& dest) {
+  Label ok;
+  testb(dest, Immediate(kHeapObjectTag));

[Ivan Posva, 2015/01/08 19:34:51]

// Check for Smi.

or as above explain the "// Non-smi case: ..." which would be even easier to
follow.

[koda, 2015/01/08 20:25:34]

Done.

+  j(ZERO, &ok, Assembler::kNearJump);
+  cmpl(dest, Immediate(Heap::kZap32Bits));
+  j(EQUAL, &ok, Assembler::kNearJump);
+  cmpl(dest, Immediate(reinterpret_cast<uint32_t>(Object::null())));
+  j(EQUAL, &ok, Assembler::kNearJump);
+  Stop("Expected zapped, Smi or null");
+  Bind(&ok);
+}
+
+
+void Assembler::VerifySmi(const Address& dest, const char* stop_msg) {
+  Label done;
+  testb(dest, Immediate(kHeapObjectTag));
+  j(ZERO, &done, Assembler::kNearJump);
+  Stop(stop_msg);
+  Bind(&done);
+}
+#endif  // defined(DEBUG)
+
+
 // Destroys the value register.
 void Assembler::StoreIntoObject(Register object,
                                 const Address& dest,
                                 Register value,
                                 bool can_value_be_smi) {
   ASSERT(object != value);
-  VerifiedWrite(dest, value);
+  VerifiedWrite(dest, value, kHeapObjectOrSmi);
   Label done;
   if (can_value_be_smi) {
     StoreIntoObjectFilter(object, value, &done);
   } else {
     StoreIntoObjectFilterNoSmi(object, value, &done);
   }
   // A store buffer update is required.
   if (value != EDX) {
     pushl(EDX);  // Preserve EDX.
   }
   if (object != EDX) {
     movl(EDX, object);
   }
   StubCode* stub_code = Isolate::Current()->stub_code();
   call(&stub_code->UpdateStoreBufferLabel());
   if (value != EDX) {
     popl(EDX);  // Restore EDX.
   }
   Bind(&done);
 }
 
 
 void Assembler::StoreIntoObjectNoBarrier(Register object,
                                          const Address& dest,
-                                         Register value) {
-  VerifiedWrite(dest, value);
+                                         Register value,
+                                         FieldContent old_content) {
+  VerifiedWrite(dest, value, old_content);
 #if defined(DEBUG)
   Label done;
   pushl(value);
   StoreIntoObjectFilter(object, value, &done);
   Stop("Store buffer update is required");
   Bind(&done);
   popl(value);
 #endif  // defined(DEBUG)
   // No store buffer update.
 }
 
 
 void Assembler::UnverifiedStoreOldObject(const Address& dest,
                                          const Object& value) {
   ASSERT(value.IsOld());
   ASSERT(!value.InVMHeap());
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0xC7);
   EmitOperand(0, dest);
   buffer_.EmitObject(value);
 }
 
 
 void Assembler::StoreIntoObjectNoBarrier(Register object,
                                          const Address& dest,
-                                         const Object& value) {
-  VerifyHeapWord(dest);
+                                         const Object& value,
+                                         FieldContent old_content) {
+  VerifyHeapWord(dest, old_content);
   if (value.IsSmi() || value.InVMHeap()) {
     Immediate imm_value(reinterpret_cast<int32_t>(value.raw()));
     movl(dest, imm_value);
     if (VerifiedMemory::enabled()) {
       Register temp = ECX;
       pushl(temp);
       leal(temp, dest);
       movl(Address(temp, VerifiedMemory::offset()), imm_value);
       popl(temp);
     }
   } else {
     UnverifiedStoreOldObject(dest, value);
     if (VerifiedMemory::enabled()) {
       Register temp = EDX;
       pushl(temp);
       leal(temp, dest);
       UnverifiedStoreOldObject(Address(temp, VerifiedMemory::offset()), value);
       popl(temp);
     }
   }
   // No store buffer update.
 }
 
 
 void Assembler::StoreIntoSmiField(const Address& dest, Register value) {
-  VerifiedWrite(dest, value);
+  VerifiedWrite(dest, value, kOnlySmi);
 #if defined(DEBUG)
-  Label done;
-  testl(value, Immediate(kHeapObjectTag));
-  j(ZERO, &done);
-  Stop("Smi expected");
-  Bind(&done);
+  VerifySmi(dest, "New value must be Smi.");

[Ivan Posva, 2015/01/08 19:34:51]

Why are you checking that the value is Smi after the write? Shouldn't we check
before so that we have a chance to see what the value is that was overwritten?

[koda, 2015/01/08 20:25:34]

Done.

 #endif  // defined(DEBUG)
 }
 
 
 void Assembler::ZeroSmiField(const Address& dest) {

[Ivan Posva, 2015/01/08 19:34:51]

Is this only used in initializing writes?

[koda, 2015/01/08 20:25:33]

Yes. Renamed to clarify this.

-  // TODO(koda): Add VerifySmi once we distinguish initalization.
-  VerifyHeapWord(dest);
+  VerifyHeapWord(dest, kEmptySmiOrNull);
   Immediate zero(Smi::RawValue(0));
   movl(dest, zero);
   if (VerifiedMemory::enabled()) {
     Register temp = ECX;
     pushl(temp);
     leal(temp, dest);
     movl(Address(temp, VerifiedMemory::offset()), zero);
     popl(temp);
   }
 }
 
 
 void Assembler::IncrementSmiField(const Address& dest, int32_t increment) {
   // Note: FlowGraphCompiler::EdgeCounterIncrementSizeInBytes depends on
   // the length of this instruction sequence.
-  // TODO(koda): Add VerifySmi once we distinguish initalization.
-  VerifyHeapWord(dest);
+  VerifyHeapWord(dest, kOnlySmi);
   Immediate inc_imm(Smi::RawValue(increment));
   addl(dest, inc_imm);
   if (VerifiedMemory::enabled()) {
     Register temp = ECX;
     pushl(temp);
     leal(temp, dest);
     addl(Address(temp, VerifiedMemory::offset()), inc_imm);
     popl(temp);
   }
 }
@@ skipping 659 matching lines @@
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_IA32