8258396: SIGILL in jdk.jfr.internal.PlatformRecorder.rotateDisk()

Reviewed-by: egahlin
Backport-of: a06cea5

Author: Jaroslav Bachorik

src/hotspot/share/jfr/recorder/storage/jfrStorage.cpp

@@ -405,7 +405,7 @@ BufferPtr JfrStorage::flush(BufferPtr cur, size_t used, size_t req, bool native,
 
 BufferPtr JfrStorage::flush_regular(BufferPtr cur, const u1* const cur_pos, size_t used, size_t req, bool native, Thread* t) {
   debug_only(assert_flush_regular_precondition(cur, cur_pos, used, req, t);)
-  // A flush is needed before memcpy since a non-large buffer is thread stable
+  // A flush is needed before memmove since a non-large buffer is thread stable
   // (thread local). The flush will not modify memory in addresses above pos()
   // which is where the "used / uncommitted" data resides. It is therefore both
   // possible and valid to migrate data after the flush. This is however only
@@ -417,7 +417,8 @@ BufferPtr JfrStorage::flush_regular(BufferPtr cur, const u1* const cur_pos, size
   if (cur->free_size() >= req) {
     // simplest case, no switching of buffers
     if (used > 0) {
-      memcpy(cur->pos(), (void*)cur_pos, used);
+      // source and destination may overlap so memmove must be used instead of memcpy
+      memmove(cur->pos(), (void*)cur_pos, used);
     }
     assert(native ? t->jfr_thread_local()->native_buffer() == cur : t->jfr_thread_local()->java_buffer() == cur, "invariant");
     return cur;