
Volume 2, Part 1: Itanium
®
Architecture-based Operating System Interaction Model with IA-32 Applications
2:263
10.6.6
Supervisor Accesses
If the processor is operating in the Itanium System Environment, supervisor override is
disabled, and LDT, GDT, TSS references are performed at the privilege level specified by
PSR.cpl. Unaligned processor references to LDT, GDT, and TSS segments will never
generate an EFLAG.ac enabled IA-32 Exception (AlignmentCheck) fault, even if PSR.cpl
equals 3 and supervisor override is disabled.
Operating systems must ensure that the GDT/LDT are mapped to pages with user level
read/write access.
Write permission is required if GDT, or LDT memory descriptor Access-bits are zero
regardless of supervisor override conditions. If all GDT/LDT descriptor Access-bits are
one, write permission can be removed. Otherwise, Access Rights, Key Miss or Key Miss
faults can be generated during all segment descriptor referencing instructions.
If a fault is generated during a supervisory access, the ISR.so bit indicates that CPL is
zero or a supervisor override condition was in effect (reference as made to GDT, LDT or
TSS).
10.6.7
Memory Alignment
Depending on software conventions, memory structures may have different alignment
or padding restrictions for the IA-32 and Itanium instruction sets. IA-32 and Itanium
architecture-based software should use aligned memory operands as much as possible
to avoid possible severe performance degradation associated with un-aligned values
and extra over-head for unaligned data memory fault handlers.
The processor provides full functional support for all cases of un-aligned IA-32 data
memory references. If PSR.ac is 1 or EFLAG.ac is 1 and CR0.am is 1and the effective
privilege level is 3, unaligned IA-32 memory references result in an IA-32 Exception
(AlignmentCheck) fault. Unaligned processor references to LDT, GDT, and TSS
segments will never generate an EFLAG.ac enabled IA-32 Exception (AlignmentCheck)
fault, even if the effective privilege level is 3 and supervisor override is disabled.
Alignment conditions for Itanium memory references are not affected by the EFLAG.ac,
CFLG.am bits.
If EFLAG.ac and CFLG.am are 1 and the reference is done at privilege level 3, IA-32
instruction set unaligned conditions are; 2-byte references not a 2-byte boundary,
4-byte references not on a 4-byte boundary, 8-byte references not on a 8-byte
boundary, and 10-byte references not on a 8-byte boundary.
If PSR.ac is 1, IA-32 instruction set unaligned conditions are; 2-byte references not a
2-byte boundary, 4-byte references not on a 4-byte boundary, 8-byte references not on
a 8-byte boundary, and 10-byte references not on a
16
-byte boundary.
The processor exhibits the following behavior when accesses are made to un-aligned
data operands that span virtual page boundaries:
• IA-32 instruction set
–
If either page contains a fault, no memory location is
modified. For reads, the destination register is not modified.
• Itanium instruction set
–
All page crossers result in an unaligned reference fault.
Memory contents and register contents are not modified.
Summary of Contents for ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS VOLUME 3 REV 2.3
Page 1: ......
Page 11: ...x Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 13: ...1 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 33: ...1 22 Volume 1 Part 1 Introduction to the Intel Itanium Architecture ...
Page 57: ...1 46 Volume 1 Part 1 Execution Environment ...
Page 147: ...1 136 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 149: ...1 138 Volume 1 Part 2 About the Optimization Guide ...
Page 191: ...1 180 Volume 1 Part 2 Predication Control Flow and Instruction Stream ...
Page 230: ......
Page 248: ...236 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 250: ...2 2 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 264: ...2 16 Volume 2 Part 1 Intel Itanium System Environment ...
Page 380: ...2 132 Volume 2 Part 1 Interruptions ...
Page 398: ...2 150 Volume 2 Part 1 Register Stack Engine ...
Page 486: ...2 238 Volume 2 Part 1 IA 32 Interruption Vector Descriptions ...
Page 750: ...2 502 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 754: ...2 506 Volume 2 Part 2 About the System Programmer s Guide ...
Page 796: ...2 548 Volume 2 Part 2 Interruptions and Serialization ...
Page 808: ...2 560 Volume 2 Part 2 Context Management ...
Page 842: ...2 594 Volume 2 Part 2 Floating point System Software ...
Page 850: ...2 602 Volume 2 Part 2 IA 32 Application Support ...
Page 862: ...2 614 Volume 2 Part 2 External Interrupt Architecture ...
Page 870: ...2 622 Volume 2 Part 2 Performance Monitoring Support ...
Page 891: ......
Page 1099: ...3 200 Volume 3 Instruction Reference padd Interruptions Illegal Operation fault ...
Page 1295: ...3 396 Volume 3 Resource and Dependency Semantics ...
Page 1296: ......
Page 1302: ...402 Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1494: ...4 192 Volume 4 Base IA 32 Instruction Reference FWAIT Wait See entry for WAIT ...
Page 1647: ...Volume 4 Base IA 32 Instruction Reference 4 345 ROL ROR Rotate See entry for RCL RCR ROL ROR ...
Page 1884: ...4 582 Volume 4 IA 32 SSE Instruction Reference ...
Page 1885: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 Index ...
Page 1886: ...Index Intel Itanium Architecture Software Developer s Manual Rev 2 3 ...
Page 1898: ...INDEX Index 12 Index for Volumes 1 2 3 and 4 ...