Fixes ABI bug in MIPS.

runtime/vm/stub_code_mips.cc

Index: runtime/vm/stub_code_mips.cc
===================================================================
--- runtime/vm/stub_code_mips.cc	(revision 32137)
+++ runtime/vm/stub_code_mips.cc	(working copy)
@@ -84,8 +84,13 @@
   // Set argv in NativeArguments.
   __ addiu(A2, A2, Immediate(exitframe_last_param_slot_from_fp * kWordSize));
 
+
   // Call runtime or redirection via simulator.
-  __ jalr(S5);
+  // We defensively always jalr through T9 because it is sometimes required by
+  // the MIPS ABI.
+  __ mov(T9, S5);
+  __ jalr(T9);
+
     ASSERT(retval_offset == 3 * kWordSize);
   // Retval is next to 1st argument.
   __ delay_slot()->addiu(A3, A2, Immediate(kWordSize));
@@ -206,8 +211,8 @@
   uword entry = reinterpret_cast<uword>(NativeEntry::NativeCallWrapper);
   entry = Simulator::RedirectExternalReference(
       entry, Simulator::kNativeCall, NativeEntry::kNumCallWrapperArguments);
-  __ LoadImmediate(T5, entry);
-  __ jalr(T5);
+  __ LoadImmediate(T9, entry);
+  __ jalr(T9);
 #else
   __ BranchLink(&NativeEntry::NativeCallWrapperLabel());
 #endif
@@ -217,8 +222,13 @@
   __ Bind(&leaf_call);
   // Call native function or redirection via simulator.
   __ ReserveAlignedFrameSpace(kWordSize);  // Just passing A0.
-  __ jalr(T5);
 
+
+  // We defensively always jalr through T9 because it is sometimes required by
+  // the MIPS ABI.
+  __ mov(T9, T5);
+  __ jalr(T9);
+
   __ Bind(&done);
 
   // Reset exit frame information in Isolate structure.
@@ -307,7 +317,11 @@
   __ ReserveAlignedFrameSpace(kWordSize);  // Just passing A0.
 
   // Call native function or redirection via simulator.
-  __ jalr(T5);
+
+  // We defensively always jalr through T9 because it is sometimes required by
+  // the MIPS ABI.
+  __ mov(T9, T5);
+  __ jalr(T9);
   __ TraceSimMsg("CallNativeCFunctionStub return");
 
   // Reset exit frame information in Isolate structure.
@@ -1023,7 +1037,11 @@
   __ Bind(&done_push_arguments);
 
   // Call the Dart code entrypoint.
-  __ jalr(A0);  // S4 is the arguments descriptor array.
+  // We defensively always jalr through T9 because it is sometimes required by
+  // the MIPS ABI (though not here in particular since we are calling Dart
+  // code).
+  __ mov(T9, A0);
+  __ jalr(T9);  // S4 is the arguments descriptor array.

[siva, 2014/01/29 22:04:03]

Here we are calling Dart code, do we need to be defensive? Can we just add a
comment stating that we are calling Dart and hence there and no MIPS ABI
requirements?

[zra, 2014/01/29 22:49:57]

Done.

   __ TraceSimMsg("InvokeDartCodeStub return");
 
   // Read the saved new Context pointer.