AIX ABI by default maps all bitfields to unsigned type regardless of their type declaration. GCC does not provide any mechanism to control this behavior. XLC controls this behavior with -qbitfield option.
-- Summary: AIX ABI defaults to unsigned bitfields Product: gcc Version: 4.5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: dje at gcc dot gnu dot org GCC build triplet: powerpc-ibm-aix GCC host triplet: powerpc-ibm-aix GCC target triplet: powerpc-ibm-aix http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42746