MIPS: Avoid use of a0 as return address in jalr.

src/mips/builtins-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_MIPS
 
@@ skipping 1006 matching lines @@
 
 
 
 static void GenerateMakeCodeYoungAgainCommon(MacroAssembler* masm) {
   // For now, we are relying on the fact that make_code_young doesn't do any
   // garbage collection which allows us to save/restore the registers without
   // worrying about which of them contain pointers. We also don't build an
   // internal frame to make the code faster, since we shouldn't have to do stack
   // crawls in MakeCodeYoung. This seems a bit fragile.
 
-  // Set a0 to point to the head of the PlatformCodeAge sequence.
+  // Set a0 to point to the head of the PlatformCodeAge sequence, using ret adr.
+  __ mov(a0, ra);
   __ Subu(a0, a0,
       Operand(kNoCodeAgeSequenceLength - Assembler::kInstrSize));
+  // Restore the original return address of the function
+  __ mov(ra, at);
 
   // The following registers must be saved and restored when calling through to
   // the runtime:
   //   a0 - contains return address (beginning of patch sequence)
   //   a1 - isolate
   RegList saved_regs =
       (a0.bit() | a1.bit() | ra.bit() | fp.bit()) & ~sp.bit();
   FrameScope scope(masm, StackFrame::MANUAL);
   __ MultiPush(saved_regs);
   __ PrepareCallCFunction(2, 0, a2);
@@ skipping 16 matching lines @@
 CODE_AGE_LIST(DEFINE_CODE_AGE_BUILTIN_GENERATOR)
 #undef DEFINE_CODE_AGE_BUILTIN_GENERATOR
 
 
 void Builtins::Generate_MarkCodeAsExecutedOnce(MacroAssembler* masm) {
   // For now, as in GenerateMakeCodeYoungAgainCommon, we are relying on the fact
   // that make_code_young doesn't do any garbage collection which allows us to
   // save/restore the registers without worrying about which of them contain
   // pointers.
 
-  // Set a0 to point to the head of the PlatformCodeAge sequence.
+  // Set a0 to point to the head of the PlatformCodeAge sequence, using ret adr.
+  __ mov(a0, ra);
   __ Subu(a0, a0,
       Operand(kNoCodeAgeSequenceLength - Assembler::kInstrSize));
+  // Restore the original return address of the function
+  __ mov(ra, at);
 
   // The following registers must be saved and restored when calling through to
   // the runtime:
   //   a0 - contains return address (beginning of patch sequence)
   //   a1 - isolate
   RegList saved_regs =
       (a0.bit() | a1.bit() | ra.bit() | fp.bit()) & ~sp.bit();
   FrameScope scope(masm, StackFrame::MANUAL);
   __ MultiPush(saved_regs);
   __ PrepareCallCFunction(2, 0, a2);
@@ skipping 777 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS