8295872: [PPC64] JfrGetCallTrace: Need pc == nullptr check before fra…

…me constructor

Backport-of: 59a13b1856cb1cf86385874b1152531016d41c22

src/hotspot/os_cpu/aix_ppc/thread_aix_ppc.cpp

@@ -32,7 +32,9 @@
 frame JavaThread::pd_last_frame() {
   assert(has_last_Java_frame(), "must have last_Java_sp() when suspended");
 
-  intptr_t* sp = Atomic::load_acquire(&_anchor._last_Java_sp);
+  // Only called by current thread or when the thread is suspended.
+  // No memory barrier needed, here. Only writer must write sp last (for use by profiler).
+  intptr_t* sp = last_Java_sp();
   address pc = _anchor.last_Java_pc();
 
   // Last_Java_pc ist not set, if we come here from compiled code.
@@ -50,9 +52,12 @@ bool JavaThread::pd_get_top_frame_for_profiling(frame* fr_addr, void* ucontext,
   // If we have a last_Java_frame, then we should use it even if
   // isInJava == true.  It should be more reliable than ucontext info.
   if (has_last_Java_frame() && frame_anchor()->walkable()) {
-    frame last_frame = pd_last_frame();
-    if (last_frame.pc() == nullptr) return false;
-    *fr_addr = last_frame;
+    intptr_t* sp = last_Java_sp();
+    address pc = _anchor.last_Java_pc();
+    // pc can be seen as null because not all writers use store pc + release store sp.
+    // Simply discard the sample in this very rare case.
+    if (pc == nullptr) return false;
+    *fr_addr = frame(sp, pc);
     return true;
   }
 

src/hotspot/os_cpu/linux_ppc/thread_linux_ppc.cpp

@@ -31,7 +31,9 @@
 frame JavaThread::pd_last_frame() {
   assert(has_last_Java_frame(), "must have last_Java_sp() when suspended");
 
-  intptr_t* sp = Atomic::load_acquire(&_anchor._last_Java_sp);
+  // Only called by current thread or when the thread is suspended.
+  // No memory barrier needed, here. Only writer must write sp last (for use by profiler).
+  intptr_t* sp = last_Java_sp();
   address pc = _anchor.last_Java_pc();
 
   // Last_Java_pc ist not set, if we come here from compiled code.
@@ -49,9 +51,12 @@ bool JavaThread::pd_get_top_frame_for_profiling(frame* fr_addr, void* ucontext,
   // If we have a last_Java_frame, then we should use it even if
   // isInJava == true.  It should be more reliable than ucontext info.
   if (has_last_Java_frame() && frame_anchor()->walkable()) {
-    frame last_frame = pd_last_frame();
-    if (last_frame.pc() == nullptr) return false;
-    *fr_addr = last_frame;
+    intptr_t* sp = last_Java_sp();
+    address pc = _anchor.last_Java_pc();
+    // pc can be seen as null because not all writers use store pc + release store sp.
+    // Simply discard the sample in this very rare case.
+    if (pc == nullptr) return false;
+    *fr_addr = frame(sp, pc);
     return true;
   }