Age code to allow reclaiming old unexecuted functions

src/ia32/codegen-ia32.cc

 // Copyright 2012 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 739 matching lines @@
   __ bind(&ascii);
   __ movzx_b(result, FieldOperand(string,
                                   index,
                                   times_1,
                                   SeqAsciiString::kHeaderSize));
   __ bind(&done);
 }
 
 #undef __
 
+
+static byte* GetNoCodeAgeSequence(uint32_t* length) {
+  // The sequence of instructions that is patched out for aging code is the
+  // following boilerplate stack-building prologue that is found both in
+  // FUNCTION and OPTIMIZED_FUNCTION code:
+  //
+  //   __ push(ebp);
+  //   __ mov(ebp, esp);
+  //   __ push(esi);
+  //   __ push(edi);
+  static byte sequence[] = { 0x55, 0x89, 0xe5, 0x56, 0x57 };
+  *length = sizeof(sequence);
+  return sequence;
+}
+
+
+byte* Code::FindPlatformCodeAgeSequence() {
+  byte* start = instruction_start();
+  uint32_t young_length;
+  byte* young_sequence = GetNoCodeAgeSequence(&young_length);
+  if (!memcmp(start, young_sequence, young_length) ||
+      *start == kCallOpcode) {
+    return start;
+  } else {
+    if (kind() == FUNCTION) {
+      byte* start_after_strict =
+          start + kSizeOfFullCodegenStrictModePrologue;
+      ASSERT(!memcmp(start_after_strict, young_sequence, young_length) ||
+             start[kSizeOfFullCodegenStrictModePrologue] == kCallOpcode);
+      return start_after_strict;
+    } else {
+      ASSERT(kind() == OPTIMIZED_FUNCTION);
+      start = instruction_start() + kSizeOfOptimizedStrictModePrologue;
+      if (!memcmp(start, young_sequence, young_length) ||
+          *start == kCallOpcode) {
+        return start;
+      }
+      start = instruction_start() + kSizeOfOptimizedAlignStackPrologue;
+      if (!memcmp(start, young_sequence, young_length) ||
+          *start == kCallOpcode) {
+        return start;
+      }
+      start = instruction_start() + kSizeOfOptimizedAlignStackPrologue +
+          kSizeOfOptimizedStrictModePrologue;
+      ASSERT(!memcmp(start, young_sequence, young_length) ||
+             *start == kCallOpcode);
+      return start;
+    }
+  }
+}
+
+
+bool Code::IsYoungSequence(byte* sequence) {
+  uint32_t young_length;
+  byte* young_sequence = GetNoCodeAgeSequence(&young_length);
+  bool result = (!memcmp(sequence, young_sequence, young_length));
+  ASSERT(result || *sequence == kCallOpcode);
+  return result;
+}
+
+
+void Code::GetCodeAgeAndParity(byte* sequence, Age* age,
+                               MarkingParity* parity) {
+  uint32_t young_length;
+  GetNoCodeAgeSequence(&young_length);
+  if (IsYoungSequence(sequence)) {
+    *age = kNoAge;
+    *parity = NO_MARKING_PARITY;
+  } else {
+    Address target_address =
+        sequence + *reinterpret_cast<int*>(sequence + 1) + young_length;
+    Code* stub = GetCodeFromTargetAddress(target_address);
+    GetCodeAgeAndParity(stub, age, parity);
+  }
+}
+
+
+void Code::PatchPlatformCodeAge(byte* sequence,
+                                Code::Age age,
+                                MarkingParity parity) {
+  uint32_t young_length;
+  byte* young_sequence = GetNoCodeAgeSequence(&young_length);
+  if (IsYoungSequence(sequence)) {
+    memcpy(sequence, young_sequence, young_length);
+  } else {
+    Code* stub = GetCodeAgeStub(age, parity);
+    Address instruction_start = stub->instruction_start();
+    int32_t stub_offset =
+        instruction_start - sequence - young_length;
+    *sequence = kCallOpcode;
+    *reinterpret_cast<int32_t*>(sequence + 1) = stub_offset;
+  }
+  CPU::FlushICache(sequence, young_length);
+}
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32