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3-420 Vol. 2A FXSAVE—Save x87 FPU, MMX Technology, SSE, and SSE2 State
INSTRUCTION SET REFERENCE, A-M
Table 3-49. Field Definitions
Field Definition
FCW x87 FPU Control Word (16 bits). See Figure 8-6 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1, for the layout of the
x87 FPU control word.
FSW x87 FPU Status Word (16 bits). See Figure 8-4 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1, for the layout of the
x87 FPU status word.
FTW x87 FPU Tag Word (8 bits). The tag information saved here is abridged, as
described in the following paragraphs. See Figure 8-7 in the Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 1, for the layout
of the x87 FPU tag word.
FOP x87 FPU Opcode (16 bits). The lower 11 bits of this field contain the
opcode, upper 5 bits are reserved. See Figure 8-8 in the Intel® 64 and IA-32
Architectures Software Developer’s Manual, Volume 1, for the layout of the
x87 FPU opcode field.
FPU IP x87 FPU Instruction Pointer Offset (32 bits). The contents of this field
differ depending on the current addressing mode (32-bit or 16-bit) of the
processor when the FXSAVE instruction was executed:
32-bit mode — 32-bit IP offset.
16-bit mode — low 16 bits are IP offset; high 16 bits are reserved.
See “x87 FPU Instruction and Operand (Data) Pointers” in Chapter 8 of the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1,
for a description of the x87 FPU instruction pointer.
CS x87 FPU Instruction Pointer Selector (16 bits).
FPU DP x87 FPU Instruction Operand (Data) Pointer Offset (32 bits). The contents
of this field differ depending on the current addressing mode (32-bit or 16-
bit) of the processor when the FXSAVE instruction was executed:
32-bit mode — 32-bit IP offset.
16-bit mode — low 16 bits are IP offset; high 16 bits are reserved.
See “x87 FPU Instruction and Operand (Data) Pointers” in Chapter 8 of the
Intel® 64 and IA-32 Architectures Software Developer’s Manual, Volume 1,
for a description of the x87 FPU operand pointer.
DS x87 FPU Instruction Operand (Data) Pointer Selector (16 bits).