According to: http://gcc.gnu.org/onlinedocs/gcc/Type-Attributes.html#Type-Attributes ms_struct is now support for also for the RS6000 back-end.
-- Summary: [4.2 Regression] attribute ms_struct is now also for rs6000 but not documented Product: gcc Version: 4.2.0 Status: UNCONFIRMED Keywords: documentation Severity: normal Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: pinskia at gcc dot gnu dot org GCC target triplet: powerpc*-*-*, rs6000-*-* http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27543