WAIT/FWAIT
Wait
| Opcode | Instruction | Op/En | 64-Bit Mode | Compat/Leg Mode | Description |
|---|---|---|---|---|---|
| 9B | WAIT | ZO | Valid | Valid | Check pending unmasked floating-point exceptions. |
| 9B | FWAIT | ZO | Valid | Valid | Check pending unmasked floating-point exceptions. |
Instruction Operand Encoding
| Op/En | Operand 1 | Operand 2 | Operand 3 | Operand 4 |
|---|---|---|---|---|
| ZO | N/A | N/A | N/A | N/A |
Description
Causes the processor to check for and handle pending, unmasked, floating-point exceptions before proceeding. (FWAIT is an alternate mnemonic for WAIT.)
This instruction is useful for synchronizing exceptions in critical sections of code. Coding a WAIT instruction after a floating-point instruction ensures that any unmasked floating-point exceptions the instruction may raise are handled before the processor can modify the instruction’s results. See the section titled “Floating-Point Exception Synchronization” in Chapter 8 of the Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, for more information on using the WAIT/FWAIT instruction.
This instruction’s operation is the same in non-64-bit modes and 64-bit mode.
Operation
CheckForPendingUnmaskedFloatingPointExceptions;
FPU Flags Affected
The C0, C1, C2, and C3 flags are undefined.
Floating-Point Exceptions
None.
Protected Mode Exceptions
| #NM | If CR0.MP[bit 1] = 1 and CR0.TS[bit 3] = 1. |
|---|---|
| #UD | If the LOCK prefix is used. |
Real-Address Mode Exceptions
Same exceptions as in protected mode.
Virtual-8086 Mode Exceptions
Same exceptions as in protected mode.
Compatibility Mode Exceptions
Same exceptions as in protected mode.
64-Bit Mode Exceptions
Same exceptions as in protected mode.
This UNOFFICIAL, mechanically-separated, non-verified reference is provided for convenience, but it may be incomplete or broken in various obvious or non-obvious ways. Refer to Intel® 64 and IA-32 Architectures Software Developer’s Manual for anything serious.