Write protect executable pages in the VM.

runtime/vm/object.cc

 // Copyright (c) 2012, 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 9543 matching lines @@
   }
   ASSERT(Object::code_class() != Class::null());
   Code& result = Code::Handle();
   {
     uword size = Code::InstanceSize(pointer_offsets_length);
     RawObject* raw = Object::Allocate(Code::kClassId, size, Heap::kOld);
     NoGCScope no_gc;
     result ^= raw;
     result.set_pointer_offsets_length(pointer_offsets_length);
     result.set_is_optimized(false);
-    result.set_is_alive(true);
+    result.set_is_alive(false);
     result.set_comments(Comments::New(0));
   }
   return result.raw();
 }
 
 
 RawCode* Code::FinalizeCode(const char* name,
                             Assembler* assembler,
                             bool optimized) {
   ASSERT(assembler != NULL);
 
-  // Allocate the Instructions object.
+  // Allocate the Code and Instructions objects.  Code is allocated first
+  // because a GC during allocation of the code will leave the instruction
+  // pages read-only.
+  intptr_t pointer_offset_count = assembler->CountPointerOffsets();
+  Code& code = Code::ZoneHandle(Code::New(pointer_offset_count));
   Instructions& instrs =
       Instructions::ZoneHandle(Instructions::New(assembler->CodeSize()));
 
   // Copy the instructions into the instruction area and apply all fixups.
   // Embedded pointers are still in handles at this point.
   MemoryRegion region(reinterpret_cast<void*>(instrs.EntryPoint()),
                       instrs.size());
   assembler->FinalizeInstructions(region);
   CPU::FlushICache(instrs.EntryPoint(), instrs.size());
 
   CodeObservers::NotifyAll(name,
                            instrs.EntryPoint(),
                            assembler->prologue_offset(),
                            instrs.size(),
                            optimized);
 
-  const ZoneGrowableArray<intptr_t>& pointer_offsets =
-      assembler->GetPointerOffsets();
-
-  // Allocate the code object.
-  Code& code = Code::ZoneHandle(Code::New(pointer_offsets.length()));
   {
     NoGCScope no_gc;
+    const ZoneGrowableArray<intptr_t>& pointer_offsets =
+        assembler->GetPointerOffsets();
+    ASSERT(pointer_offsets.length() == pointer_offset_count);
+    ASSERT(code.pointer_offsets_length() == pointer_offsets.length());
 
     // Set pointer offsets list in Code object and resolve all handles in
     // the instruction stream to raw objects.
-    ASSERT(code.pointer_offsets_length() == pointer_offsets.length());
     for (intptr_t i = 0; i < pointer_offsets.length(); i++) {
       intptr_t offset_in_instrs = pointer_offsets[i];
       code.SetPointerOffsetAt(i, offset_in_instrs);
       const Object* object = region.Load<const Object*>(offset_in_instrs);
       region.Store<RawObject*>(offset_in_instrs, object->raw());
     }
 
     // Hook up Code and Instructions objects.
     instrs.set_code(code.raw());
     code.set_instructions(instrs.raw());
+    code.set_is_alive(true);
 
     // Set object pool in Instructions object.
     const GrowableObjectArray& object_pool = assembler->object_pool();
     if (object_pool.IsNull()) {
       instrs.set_object_pool(Object::empty_array().raw());
     } else {
       // TODO(regis): Once MakeArray takes a Heap::Space argument, call it here
       // with Heap::kOld and change the ARM and MIPS assemblers to work with a
       // GrowableObjectArray in new space.
       instrs.set_object_pool(Array::MakeArray(object_pool));
     }
+    bool status =
+        VirtualMemory::Protect(reinterpret_cast<void*>(instrs.raw_ptr()),
+                               instrs.raw()->Size(),
+                               VirtualMemory::kReadExecute);
+    ASSERT(status);
   }
   return code.raw();
 }
 
 
 RawCode* Code::FinalizeCode(const Function& function,
                             Assembler* assembler,
                             bool optimized) {
   // Calling ToFullyQualifiedCString is very expensive, try to avoid it.
   if (CodeObservers::AreActive()) {
@@ skipping 6420 matching lines @@
   return "_MirrorReference";
 }
 
 
 void MirrorReference::PrintToJSONStream(JSONStream* stream, bool ref) const {
   Instance::PrintToJSONStream(stream, ref);
 }
 
 
 }  // namespace dart