4:76
Volume 4: Base IA-32 Instruction Reference
CMPXCHG8B—Compare and Exchange 8 Bytes
Description
Compares the 64-bit value in EDX:EAX with the operand (destination operand). If the
values are equal, the 64-bit value in ECX:EBX is stored in the destination operand.
Otherwise, the value in the destination operand is loaded into EDX:EAX. The destination
operand is an 8-byte memory location. For the EDX:EAX and ECX:EBX register pairs,
EDX and ECX contain the high-order 32 bits and EAX and EBX contain the low-order 32
bits of a 64-bit value.
This instruction can be used with a LOCK prefix to allow the instruction to be executed
atomically. To simplify the interface to the processor’s bus, the destination operand
receives a write cycle without regard to the result of the comparison. The destination
operand is written back if the comparison fails; otherwise, the source operand is written
into the destination. (The processor never produces a locked read without also
producing a locked write.)
Operation
IF Itanium System Environment AND External_Atomic_Lock_Required AND DCR.lc
THEN IA-32_Intercept(LOCK,CMPXCHG);
IF (EDX:EAX = DEST)
ZF
1
DEST
ECX:EBX
ELSE
ZF
0
EDX:EAX
DEST
FI;
Flags Affected
The ZF flag is set if the destination operand and EDX:EAX are equal; otherwise it is
cleared. The CF, PF, AF, SF, and OF flags are unaffected.
Additional Itanium System Environment Exceptions
Itanium Reg Faults NaT Register Consumption Abort.
Itanium Mem FaultsVHPT Data Fault, Nested TLB Fault, Data TLB Fault, Alternate Data
TLB Fault, Data Page Not Present Fault, Data NaT Page Consumption
Abort, Data Key Miss Fault, Data Key Permission Fault, Data Access
Rights Fault, Data Access Bit Fault, Data Dirty Bit Fault
IA-32_Intercept
Lock Intercept
–
If an external atomic bus lock is required to
complete this operation and DCR.lc is 1, no atomic transaction
occurs, this instruction is faulted and an IA-32_Intercept(Lock) fault
is generated. The software lock handler is responsible for the
emulation of this instruction
Opcode
Instruction
Description
0F C7 /1 m64
CMPXCHG8B
m64
Compare EDX:EAX with
m64
. If equal, set ZF and load
ECX:EBX into
m64
. Else, clear ZF and load
m64
into
EDX:EAX.
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 ...