144 lines
6.8 KiB
HTML
144 lines
6.8 KiB
HTML
<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml" xmlns:svg="http://www.w3.org/2000/svg" xmlns:x86="http://www.felixcloutier.com/x86"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><link rel="stylesheet" type="text/css" href="style.css"></link><title>FRSTOR
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— Restore x87 FPU State</title></head><body><header><nav><ul><li><a href='index.html'>Index</a></li><li>December 2023</li></ul></nav></header><h1>FRSTOR
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— Restore x87 FPU State</h1>
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<table>
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<tr>
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<th>Opcode </th>
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<th></th>
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<th>Mode</th>
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<th>Leg Mode</th>
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<th>Description</th></tr>
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<tr>
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<td>DD /4 </td>
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<td></td>
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<td></td>
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<td></td>
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<td>Load FPU state from m94byte or m108byte.</td></tr></table>
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<h2 id="description">Description<a class="anchor" href="#description">
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¶
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</a></h2>
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<p>Loads the FPU state (operating environment and register stack) from the memory area specified with the source operand. This state data is typically written to the specified memory location by a previous FSAVE/FNSAVE instruction.</p>
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<p>The FPU operating environment consists of the FPU control word, status word, tag word, instruction pointer, data pointer, and last opcode. Figures 8-9 through 8-12 in the Intel<sup>®</sup> 64 and IA-32 Architectures Software Developer’s Manual, Volume 1, show the layout in memory of the stored environment, depending on the operating mode of the processor (protected or real) and the current operand-size attribute (16-bit or 32-bit). In virtual-8086 mode, the real mode layouts are used. The contents of the FPU register stack are stored in the 80 bytes immediately following the operating environment image.</p>
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<p>The FRSTOR instruction should be executed in the same operating mode as the corresponding FSAVE/FNSAVE instruction.</p>
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<p>If one or more unmasked exception bits are set in the new FPU status word, a floating-point exception will be generated upon execution of the next floating-point instruction (except for the no-wait floating-point instructions, see the section titled “Software Exception Handling” in Chapter 8 of the Intel<sup>®</sup> 64 and IA-32 Architectures Software Developer’s Manual, Volume 1). To avoid raising exceptions when loading a new operating environment, clear all the exception flags in the FPU status word that is being loaded.</p>
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<p>This instruction’s operation is the same in non-64-bit modes and 64-bit mode.</p>
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<h2 id="operation">Operation<a class="anchor" href="#operation">
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¶
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</a></h2>
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<pre>FPUControlWord := SRC[FPUControlWord];
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FPUStatusWord := SRC[FPUStatusWord];
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FPUTagWord := SRC[FPUTagWord];
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FPUDataPointer := SRC[FPUDataPointer];
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FPUInstructionPointer := SRC[FPUInstructionPointer];
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FPULastInstructionOpcode := SRC[FPULastInstructionOpcode];
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ST(0) := SRC[ST(0)];
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ST(1) := SRC[ST(1)];
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ST(2) := SRC[ST(2)];
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ST(3) := SRC[ST(3)];
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ST(4) := SRC[ST(4)];
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ST(5) := SRC[ST(5)];
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ST(6) := SRC[ST(6)];
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ST(7) := SRC[ST(7)];
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</pre>
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<h2 id="fpu-flags-affected">FPU Flags Affected<a class="anchor" href="#fpu-flags-affected">
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¶
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</a></h2>
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<p>The C0, C1, C2, C3 flags are loaded.</p>
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<h2 class="exceptions" id="floating-point-exceptions">Floating-Point Exceptions<a class="anchor" href="#floating-point-exceptions">
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¶
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</a></h2>
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<p>None; however, if an unmasked exception is loaded in the status word, it is generated upon execution of the next “waiting” floating-point instruction.</p>
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<h2 class="exceptions" id="protected-mode-exceptions">Protected Mode Exceptions<a class="anchor" href="#protected-mode-exceptions">
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¶
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</a></h2>
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<table>
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<tr>
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<td rowspan="2">#GP(0)</td>
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<td>If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.</td></tr>
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<tr>
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<td>If the DS, ES, FS, or GS register is used to access memory and it contains a NULL segment selector.</td></tr>
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<tr>
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<td>#SS(0)</td>
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<td>If a memory operand effective address is outside the SS segment limit.</td></tr>
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<tr>
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<td>#NM</td>
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<td>CR0.EM[bit 2] or CR0.TS[bit 3] = 1.</td></tr>
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<tr>
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<td>#PF(fault-code)</td>
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<td>If a page fault occurs.</td></tr>
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<tr>
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<td>#AC(0)</td>
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<td>If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.</td></tr>
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<tr>
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<td>#UD</td>
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<td>If the LOCK prefix is used.</td></tr></table>
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<h2 class="exceptions" id="real-address-mode-exceptions">Real-Address Mode Exceptions<a class="anchor" href="#real-address-mode-exceptions">
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¶
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</a></h2>
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<table>
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<tr>
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<td>#GP</td>
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<td>If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.</td></tr>
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<tr>
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<td>#SS</td>
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<td>If a memory operand effective address is outside the SS segment limit.</td></tr>
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<tr>
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<td>#NM</td>
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<td>CR0.EM[bit 2] or CR0.TS[bit 3] = 1.</td></tr>
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<tr>
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<td>#UD</td>
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<td>If the LOCK prefix is used.</td></tr></table>
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<h2 class="exceptions" id="virtual-8086-mode-exceptions">Virtual-8086 Mode Exceptions<a class="anchor" href="#virtual-8086-mode-exceptions">
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¶
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</a></h2>
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<table>
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<tr>
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<td>#GP(0)</td>
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<td>If a memory operand effective address is outside the CS, DS, ES, FS, or GS segment limit.</td></tr>
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<tr>
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<td>#SS(0)</td>
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<td>If a memory operand effective address is outside the SS segment limit.</td></tr>
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<tr>
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<td>#NM</td>
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<td>CR0.EM[bit 2] or CR0.TS[bit 3] = 1.</td></tr>
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<tr>
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<td>#PF(fault-code)</td>
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<td>If a page fault occurs.</td></tr>
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<tr>
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<td>#AC(0)</td>
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<td>If alignment checking is enabled and an unaligned memory reference is made.</td></tr>
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<tr>
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<td>#UD</td>
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<td>If the LOCK prefix is used.</td></tr></table>
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<h2 class="exceptions" id="compatibility-mode-exceptions">Compatibility Mode Exceptions<a class="anchor" href="#compatibility-mode-exceptions">
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¶
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</a></h2>
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<p>Same exceptions as in protected mode.</p>
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<h2 class="exceptions" id="64-bit-mode-exceptions">64-Bit Mode Exceptions<a class="anchor" href="#64-bit-mode-exceptions">
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¶
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</a></h2>
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<table>
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<tr>
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<td>#SS(0)</td>
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<td>If a memory address referencing the SS segment is in a non-canonical form.</td></tr>
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<tr>
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<td>#GP(0)</td>
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<td>If the memory address is in a non-canonical form.</td></tr>
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<tr>
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<td>#NM</td>
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<td>CR0.EM[bit 2] or CR0.TS[bit 3] = 1.</td></tr>
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<tr>
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<td>#PF(fault-code)</td>
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<td>If a page fault occurs.</td></tr>
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<tr>
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<td>#AC(0)</td>
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<td>If alignment checking is enabled and an unaligned memory reference is made while the current privilege level is 3.</td></tr>
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<tr>
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<td>#UD</td>
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<td>If the LOCK prefix is used.</td></tr></table><footer><p>
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This UNOFFICIAL, mechanically-separated, non-verified reference is provided for convenience, but it may be
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inc<span style="opacity: 0.2">omp</span>lete or b<sub>r</sub>oke<sub>n</sub> in various obvious or non-obvious
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ways. Refer to <a href="https://software.intel.com/en-us/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-1-2a-2b-2c-2d-3a-3b-3c-3d-and-4">Intel® 64 and IA-32 Architectures Software Developer’s Manual</a> for anything serious.
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</p></footer></body></html>
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