Intel 64 and IA-32 Architectures Software Developers Manual Volume 2A, Instruction Set Reference, A-M

Vol. 2 3-425
INSTRUCTION SET REFERENCE, A-M
#AC If this exception is disabled a general protection exception
(#GP) is signaled if the memory operand is not aligned on a
16-byte boundary, as described above. If the alignment check
exception (#AC) is enabled (and the CPL is 3), signaling of #AC
is not guaranteed and may vary with implementation, as
follows. In all implementations where #AC is not signaled, a
general protection exception is signaled in its place. In addition,
the width of the alignment check may also vary with implemen-
tation. For instance, for a given implementation, an alignment
check exception might be signaled for a 2-byte misalignment,
whereas a general protection exception might be signaled for all
other misalignments (4-, 8-, or 16-byte misalignments).
Implementation Note
The order in which the processor signals general-protection (#GP) and page-fault
(#PF) exceptions when they both occur on an instruction boundary is given in Table
5-2 in the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume
3B. This order vary for FXSAVE for different processor implementations.