Fix x64 patching of asllocation stub: the pool pointer must be set-up before patching jump is execu…

runtime/vm/stub_code_x64.cc

Index: runtime/vm/stub_code_x64.cc
===================================================================
--- runtime/vm/stub_code_x64.cc	(revision 40325)
+++ runtime/vm/stub_code_x64.cc	(working copy)
@@ -1067,8 +1067,32 @@
 // Input parameters:
 //   RSP + 8 : type arguments object (only if class is parameterized).
 //   RSP : points to return address.
-uword StubCode::GenerateAllocationStubForClass(Assembler* assembler,
-                                              const Class& cls) {
+void StubCode::GenerateAllocationStubForClass(
+    Assembler* assembler, const Class& cls,
+    uword* entry_patch_offset, uword* patch_code_pc_offset) {
+  // Must set-up a PP before being able to patch.
+  Register new_pp = R13;
+  Register new_pc = R12;
+
+  Label next;
+  __ nop(4);  // Need a fixed size sequence on frame entry.
+  __ call(&next);
+  __ Bind(&next);
+
+  const intptr_t object_pool_pc_dist =
+      Instructions::HeaderSize() - Instructions::object_pool_offset() +
+      __ CodeSize();
+  const intptr_t offset =
+      Assembler::EntryPointToPcMarkerOffset() - __ CodeSize();
+  __ popq(new_pc);
+  if (offset != 0) {
+    __ addq(new_pc, Immediate(offset));
+  }
+
+  // Load pool pointer.
+  __ movq(new_pp, Address(new_pc, -object_pool_pc_dist - offset));
+  *entry_patch_offset = assembler->CodeSize();

[zra, 2014/09/16 20:55:58]

Since this is a delicate bit of code, I'd recommend adding a function to the x64
assembler instead of duplicating from EmitFrameEntry. (It also appears in the
else-if case in EmitFrameEntry, but duplicating there is possibly not as bad
since they're right next to each other).

[srdjan, 2014/09/16 21:54:50]

Good suggestion! Done.

+
   const intptr_t kObjectTypeArgumentsOffset = 1 * kWordSize;
   // The generated code is different if the class is parameterized.
   const bool is_cls_parameterized = cls.NumTypeArguments() > 0;
@@ -1180,10 +1204,9 @@
   // Restore the frame pointer.
   __ LeaveStubFrame();
   __ ret();
-  uword patch_code_pc_offset = assembler->CodeSize();
+  *patch_code_pc_offset = assembler->CodeSize();
   StubCode* stub_code = Isolate::Current()->stub_code();
-  __ JmpPatchable(&stub_code->FixAllocationStubTargetLabel(), R13);
-  return patch_code_pc_offset;
+  __ JmpPatchable(&stub_code->FixAllocationStubTargetLabel(), new_pp);
 }