AIX has different alignment rules regarding double structure members which are not the first member.
AIX supports "#pragma align (natural)" which we use since JDK-8318175. That makes the structure layouts compatible with linux.
AIX also supports "#pragma align (power)" which is the default. If this alignment mode is used double structure members which are not the first member are only 4 Byte aligned.
The modes are also described here: https://www.ibm.com/docs/en/xl-c-and-cpp-aix/16.1?topic=data-using-alignment-modes

JDK-8317545 supports both modes, but we have no test for the "#pragma align (power)" mode, yet.