Support stripped binaries and remove unneeded attributes.

Attribute optimize(0) doesn't appear to be helpful helpful.  This
prevents optimization in the function but not at call sites to the
function.  The function may still be inlined since it has no side
effect (in some cases that we currently don't support).

Having a side effect prevents a call site optimization that allows
removal of a noinline function call with no side effect.  Call site
optimization should only happen (in GCC at least) when using whole
program optimization so this may be stronger than we strictly need.

Also added _amdgpu_r_debug to the exported symbol list (global) and
switched to the standard macro for an exported symbol (HSA_API).
Without being in the global list the debugger will not find this
symbol if the binary has been stripped.

Change-Id: Ieb00175ccc55fda4491deee44711cd55b3f24aeb

runtime/hsa-runtime/loader/executable.cpp

@@ -62,18 +62,17 @@
 using namespace amd::hsa;
 using namespace amd::hsa::common;
 
-#if defined __clang__
-#define NONOPTIMIZE __attribute__((noinline, optnone))
-#else
-#define NONOPTIMIZE __attribute__((noinline, optimize(0)))
-#endif
-
-NONOPTIMIZE static void _loader_debug_state() {};
-r_debug _amdgpu_r_debug __attribute__((visibility("default"))) = {1,
-                                                                  nullptr,
-                                                                  reinterpret_cast<uintptr_t>(&_loader_debug_state),
-                                                                  r_debug::RT_CONSISTENT,
-                                                                  0};
+// Having a side effect prevents call site optimization that allows removal of a noinline function call
+// with no side effect.
+__attribute__((noinline)) static void _loader_debug_state() {
+  static volatile int function_needs_a_side_effect = 0;
+  function_needs_a_side_effect ^= 1;
+}
+HSA_API r_debug _amdgpu_r_debug = {1,
+                           nullptr,
+                           reinterpret_cast<uintptr_t>(&_loader_debug_state),
+                           r_debug::RT_CONSISTENT,
+                           0};
 static link_map* r_debug_tail = nullptr;
 
 namespace amd {