Adds debugger patching to arm64.

runtime/vm/assembler_arm64.h

 // Copyright (c) 2014, 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.
 
 #ifndef VM_ASSEMBLER_ARM64_H_
 #define VM_ASSEMBLER_ARM64_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_arm64.h directly; use assembler.h instead.
 #endif
@@ skipping 770 matching lines @@
   }
 
   void SmiUntag(Register reg) {
     Asr(reg, reg, kSmiTagSize);
   }
   void SmiTag(Register reg) {
     Lsl(reg, reg, kSmiTagSize);
   }
 
   // Branching to ExternalLabels.
-  void BranchPatchable(const ExternalLabel* label, Register pp) {
-    LoadExternalLabel(TMP, label, kPatchable, pp);
-    br(TMP);
-  }
-
   void Branch(const ExternalLabel* label, Register pp) {
     LoadExternalLabel(TMP, label, kNotPatchable, pp);
     br(TMP);
   }
 
   // Fixed length branch to label.
-  void BranchFixed(const ExternalLabel* label) {
+  void BranchPatchable(const ExternalLabel* label) {
+    // TODO(zra): Use LoadExternalLabelFixed if possible.
     LoadImmediateFixed(TMP, label->address());
     br(TMP);
   }
 
   void BranchLink(const ExternalLabel* label, Register pp) {
     if (Isolate::Current() == Dart::vm_isolate()) {
       LoadImmediate(TMP, label->address(), kNoPP);
       blr(TMP);
     } else {
       LoadExternalLabel(TMP, label, kNotPatchable, pp);
       blr(TMP);
     }
   }
 
+  // BranchLinkPatchable must be a fixed-length sequence so we can patch it
+  // with the debugger.
   void BranchLinkPatchable(const ExternalLabel* label) {
-    LoadExternalLabel(TMP, label, kPatchable, PP);
+    LoadExternalLabelFixed(TMP, label, kPatchable, PP);
     blr(TMP);
   }
 
   // Macros accepting a pp Register argument may attempt to load values from
   // the object pool when possible. Unless you are sure that the untagged object
   // pool pointer is in another register, or that it is not available at all,
   // PP should be passed for pp.
   void AddImmediate(Register dest, Register rn, int64_t imm, Register pp);
   void AddImmediateSetFlags(
       Register dest, Register rn, int64_t imm, Register pp);
@@ skipping 71 matching lines @@
 
   // Index of constant pool entries pointing to debugger stubs.
   static const int kBreakpointRuntimeCPIndex = 5;
 
   enum Patchability {
     kPatchable,
     kNotPatchable,
   };
 
   void LoadWordFromPoolOffset(Register dst, Register pp, uint32_t offset);
+  void LoadWordFromPoolOffsetFixed(Register dst, Register pp, uint32_t offset);
   intptr_t FindExternalLabel(const ExternalLabel* label,
                              Patchability patchable);
   intptr_t FindObject(const Object& obj, Patchability patchable);
   intptr_t FindImmediate(int64_t imm);
   bool CanLoadObjectFromPool(const Object& object);
   bool CanLoadImmediateFromPool(int64_t imm, Register pp);
   void LoadExternalLabel(Register dst, const ExternalLabel* label,
                          Patchability patchable, Register pp);
+  void LoadExternalLabelFixed(Register dst,
+                              const ExternalLabel* label,
+                              Patchability patchable,
+                              Register pp);
   void LoadObject(Register dst, const Object& obj, Register pp);
   void LoadDecodableImmediate(Register reg, int64_t imm, Register pp);
   void LoadImmediateFixed(Register reg, int64_t imm);
   void LoadImmediate(Register reg, int64_t imm, Register pp);
   void LoadDImmediate(VRegister reg, double immd, Register pp);
 
   void PushObject(const Object& object, Register pp) {
     LoadObject(TMP, object, pp);
     Push(TMP);
   }
@@ skipping 415 matching lines @@
                                   Register value,
                                   Label* no_update);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_ARM64_H_