Merge pull request #158 from dicej/armv7

use armv7 memory barriers by default

README.md

@@ -127,6 +127,10 @@ devices.  See [here](https://github.com/ReadyTalk/hello-ios) for an
 example of an Xcode project for iOS which uses Avian.  
     * _default:_ false
 
+  * `armv6` - if true, don't use any instructions newer than armv6.  By
+default, we assume the target is armv7 or later, and thus requires explicit
+memory barrier instructions to ensure cache coherency
+
   * `bootimage` - if true, create a boot image containing the pre-parsed
 class library and ahead-of-time compiled methods.  This option is
 only valid for process=compile builds.  Note that you may need to

makefile

@@ -470,6 +470,10 @@ ifeq ($(arch),arm)
 	endif
 endif
 
+ifeq ($(armv6),true)
+	cflags += -DAVIAN_ASSUME_ARMV6
+endif
+
 ifeq ($(ios),true)
 	cflags += -DAVIAN_IOS
 	use-lto = false
@@ -1895,6 +1899,7 @@ $(bootimage-generator): $(bootimage-generator-objects) $(vm-objects)
 		arch=$(build-arch) \
 		aot-only=false \
 		target-arch=$(arch) \
+		armv6=$(armv6) \
 		platform=$(bootimage-platform) \
 		target-format=$(target-format) \
 		openjdk=$(openjdk) \

src/avian/arm.h

@@ -79,11 +79,25 @@ trap()
 #endif
 }
 
+// todo: determine the minimal operation types and domains needed to
+// implement the following barriers (see
+// http://community.arm.com/groups/processors/blog/2011/10/19/memory-access-ordering-part-3--memory-access-ordering-in-the-arm-architecture).
+// For now, we just use DMB SY as a conservative but not necessarily
+// performant choice.
+
 #ifndef _MSC_VER
 inline void
 memoryBarrier()
 {
-  asm("nop");
+#ifdef __APPLE__
+  OSMemoryBarrier();
+#elif (__GNUC__ >= 4) && (__GNUC_MINOR__ >= 1)
+  return __sync_synchronize();
+#elif (! defined AVIAN_ASSUME_ARMV6)
+  __asm__ __volatile__ ("dmb" : : : "memory");
+#else
+  __asm__ __volatile__ ("" : : : "memory");
+#endif
 }
 #endif
 
@@ -148,7 +162,7 @@ inline bool
 atomicCompareAndSwap32(uint32_t* p, uint32_t old, uint32_t new_)
 {
 #ifdef __APPLE__
-  return OSAtomicCompareAndSwap32(old, new_, reinterpret_cast<int32_t*>(p));
+  return OSAtomicCompareAndSwap32Barrier(old, new_, reinterpret_cast<int32_t*>(p));
 #elif (defined __QNX__)
   return old == _smp_cmpxchg(p, old, new_);
 #else

src/codegen/target/arm/encode.h

@@ -172,6 +172,8 @@ inline int blo(int offset) { return SETCOND(b(offset), CC); }
 inline int bhs(int offset) { return SETCOND(b(offset), CS); }
 inline int bpl(int offset) { return SETCOND(b(offset), PL); }
 inline int fmstat() { return fmrx(15, FPSCR); }
+// todo: make this pretty:
+inline int dmb() { return 0xf57ff05f; }
 
 } // namespace isa
 

src/codegen/target/arm/multimethod.cpp

@@ -58,9 +58,9 @@ void populateTables(ArchitectureContext* con) {
   BranchOperationType* bro = con->branchOperations;
 
   zo[lir::Return] = return_;
-  zo[lir::LoadBarrier] = memoryBarrier;
-  zo[lir::StoreStoreBarrier] = memoryBarrier;
-  zo[lir::StoreLoadBarrier] = memoryBarrier;
+  zo[lir::LoadBarrier] = loadBarrier;
+  zo[lir::StoreStoreBarrier] = storeStoreBarrier;
+  zo[lir::StoreLoadBarrier] = storeLoadBarrier;
   zo[lir::Trap] = trap;
 
   uo[Multimethod::index(lir::LongCall, C)] = CAST1(longCallC);

src/codegen/target/arm/operations.cpp

@@ -1228,7 +1228,33 @@ void trap(Context* con)
   emit(con, bkpt(0));
 }
 
-void memoryBarrier(Context*) {}
+// todo: determine the minimal operation types and domains needed to
+// implement the following barriers (see
+// http://community.arm.com/groups/processors/blog/2011/10/19/memory-access-ordering-part-3--memory-access-ordering-in-the-arm-architecture).
+// For now, we just use DMB SY as a conservative but not necessarily
+// performant choice.
+
+void memoryBarrier(Context* con UNUSED)
+{
+#ifndef AVIAN_ASSUME_ARMV6
+  emit(con, dmb());
+#endif
+}
+
+void loadBarrier(Context* con)
+{
+  memoryBarrier(con);
+}
+
+void storeStoreBarrier(Context* con)
+{
+  memoryBarrier(con);
+}
+
+void storeLoadBarrier(Context* con)
+{
+  memoryBarrier(con);
+}
 
 } // namespace arm
 } // namespace codegen

src/codegen/target/arm/operations.h

@@ -230,7 +230,11 @@ void return_(Context* con);
 
 void trap(Context* con);
 
-void memoryBarrier(Context*);
+void loadBarrier(Context*);
+
+void storeStoreBarrier(Context*);
+
+void storeLoadBarrier(Context*);
 
 } // namespace arm
 } // namespace codegen