[ia32,root] Initialize kRootRegister and verify through IsolateData

With this CL we finally actually set the root register to the correct
value.  Verification is still preserved by keeping a magic number in
IsolateData.

Bug: v8:6666
Change-Id: I89cb7cb36f977ac677ec33a814a2798baab4cec4
Reviewed-on: https://chromium-review.googlesource.com/c/1278277Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56627}

src/ia32/code-stubs-ia32.cc

@@ -31,23 +31,27 @@ void JSEntryStub::Generate(MacroAssembler* masm) {
 
   ProfileEntryHookStub::MaybeCallEntryHook(masm);
 
-  // Set up frame.
-  __ push(ebp);
-  __ mov(ebp, esp);
-
-  // Push marker in two places.
-  StackFrame::Type marker = type();
-  __ push(Immediate(StackFrame::TypeToMarker(marker)));  // marker
-  ExternalReference context_address =
-      ExternalReference::Create(IsolateAddressId::kContextAddress, isolate());
-  __ push(__ StaticVariable(context_address));  // context
-  // Save callee-saved registers (C calling conventions).
-  __ push(edi);
-  __ push(esi);
-  Assembler::AllowExplicitEbxAccessScope spill_register(masm);
-  __ push(ebx);
-
-  __ InitializeRootRegister();
+  {  // NOLINT. Scope block confuses linter.
+    NoRootArrayScope uninitialized_root_register(masm);
+    Assembler::AllowExplicitEbxAccessScope spill_register(masm);
+
+    // Set up frame.
+    __ push(ebp);
+    __ mov(ebp, esp);
+
+    // Push marker in two places.
+    StackFrame::Type marker = type();
+    __ push(Immediate(StackFrame::TypeToMarker(marker)));  // marker
+    ExternalReference context_address =
+        ExternalReference::Create(IsolateAddressId::kContextAddress, isolate());
+    __ push(__ StaticVariable(context_address));  // context
+    // Save callee-saved registers (C calling conventions).
+    __ push(edi);
+    __ push(esi);
+    __ push(ebx);
+
+    __ InitializeRootRegister();
+  }
   Assembler::SupportsRootRegisterScope supports_root_register(masm);
 
   // Save copies of the top frame descriptor on the stack.

src/ia32/constants-ia32.h

@@ -15,10 +15,6 @@ namespace internal {
 // currently no root register is present.
 constexpr int kRootRegisterBias = 0;
 
-// Used temporarily to track clobbering of the root register.
-// TODO(v8:6666): Remove this once use the root register.
-constexpr size_t kRootRegisterSentinel = 0xcafeca11;
-
 // TODO(sigurds): Change this value once we use relative jumps.
 constexpr size_t kMaxPCRelativeCodeRangeInMB = 0;
 }  // namespace internal

src/ia32/macro-assembler-ia32.cc

@@ -41,14 +41,33 @@ MacroAssembler::MacroAssembler(Isolate* isolate,
     code_object_ = Handle<HeapObject>::New(
         *isolate->factory()->NewSelfReferenceMarker(), isolate);
   }
+}
+
+void TurboAssembler::InitializeRootRegister() {
+  // TODO(v8:6666): Initialize unconditionally once poisoning support has been
+  // removed.
+  if (!FLAG_embedded_builtins) return;
 
-#ifdef V8_EMBEDDED_BUILTINS
-  // Fake it as long as we use indirections through an embedded external
-  // reference. This will let us implement indirections without a real
-  // root register.
-  // TODO(jgruber, v8:6666): Remove once a real root register exists.
-  if (FLAG_embedded_builtins) set_root_array_available(true);
-#endif  // V8_EMBEDDED_BUILTINS
+  Assembler::AllowExplicitEbxAccessScope setup(this);
+  ExternalReference roots_array_start =
+      ExternalReference::roots_array_start(isolate());
+  Move(kRootRegister, Immediate(roots_array_start));
+  add(kRootRegister, Immediate(kRootRegisterBias));
+}
+
+void TurboAssembler::VerifyRootRegister() {
+  if (!FLAG_ia32_verify_root_register) return;
+
+  DCHECK(FLAG_embedded_builtins);
+
+  Assembler::AllowExplicitEbxAccessScope read_only_access(this);
+  Label root_register_ok;
+  cmp(Operand(kRootRegister,
+              IsolateData::kMagicNumberOffset - kRootRegisterBias),
+      Immediate(IsolateData::kRootRegisterSentinel));
+  j(equal, &root_register_ok);
+  int3();
+  bind(&root_register_ok);
 }
 
 void TurboAssembler::LoadRoot(Register destination, RootIndex index) {

src/ia32/macro-assembler-ia32.h

@@ -110,26 +110,6 @@ class V8_EXPORT_PRIVATE TurboAssembler : public TurboAssemblerBase {
   // Check that the stack is aligned.
   void CheckStackAlignment();
 
-  void InitializeRootRegister() {
-    Assembler::AllowExplicitEbxAccessScope setup(this);
-    // For now, only check sentinel value for root register.
-    // TODO(jgruber,v8:6666): Implement root register.
-    if (FLAG_ia32_verify_root_register && FLAG_embedded_builtins) {
-      mov(kRootRegister, kRootRegisterSentinel);
-    }
-  }
-
-  void VerifyRootRegister() {
-    if (FLAG_ia32_verify_root_register && FLAG_embedded_builtins) {
-      Assembler::AllowExplicitEbxAccessScope read_only_access(this);
-      Label root_register_ok;
-      cmp(kRootRegister, kRootRegisterSentinel);
-      j(equal, &root_register_ok);
-      int3();
-      bind(&root_register_ok);
-    }
-  }
-
   // Move a constant into a destination using the most efficient encoding.
   void Move(Register dst, const Immediate& src);
   void Move(Register dst, Smi* src) { Move(dst, Immediate(src)); }
@@ -244,6 +224,11 @@ class V8_EXPORT_PRIVATE TurboAssembler : public TurboAssemblerBase {
 
   void Ret();
 
+  // Root register utility functions.
+
+  void InitializeRootRegister();
+  void VerifyRootRegister();
+
   void LoadRoot(Register destination, RootIndex index) override;
 
   // Indirect root-relative loads.

src/isolate-data.h

@@ -37,6 +37,9 @@ class IsolateData final {
   /* builtins_ */                                                         \
   V(kBuiltinsTableOffset, Builtins::builtin_count* kPointerSize)          \
   V(kBuiltinsTableEndOffset, 0)                                           \
+  /* magic_number_ */                                                     \
+  V(kMagicNumberOffset, kIntptrSize)                                      \
+  V(kMagicNumberEndOffset, 0)                                             \
   /* Total size. */                                                       \
   V(kSize, 0)
 
@@ -61,6 +64,10 @@ class IsolateData final {
 
   Object** builtins() { return &builtins_[0]; }
 
+  // For root register verification.
+  // TODO(v8:6666): Remove once the root register is fully supported on ia32.
+  static constexpr intptr_t kRootRegisterSentinel = 0xcafeca11;
+
  private:
   RootsTable roots_;
 
@@ -68,6 +75,10 @@ class IsolateData final {
 
   Object* builtins_[Builtins::builtin_count];
 
+  // For root register verification.
+  // TODO(v8:6666): Remove once the root register is fully supported on ia32.
+  const intptr_t magic_number_ = kRootRegisterSentinel;
+
   V8_INLINE static void AssertPredictableLayout();
 
   friend class Isolate;