forked from NRZCode/ia32-64
102 lines
3.9 KiB
HTML
102 lines
3.9 KiB
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>CLAC
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— Clear AC Flag in EFLAGS Register</title></head><body><header><nav><ul><li><a href='index.html'>Index</a></li><li>December 2023</li></ul></nav></header><h1>CLAC
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— Clear AC Flag in EFLAGS Register</h1>
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<table>
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<tr>
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<th>Opcode/Instruction</th>
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<th>Op / En</th>
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<th>64/32 bit Mode Support</th>
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<th>CPUID Feature Flag</th>
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<th>Description</th></tr>
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<tr>
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<td>NP 0F 01 CA CLAC</td>
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<td>ZO</td>
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<td>V/V</td>
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<td>SMAP</td>
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<td>Clear the AC flag in the EFLAGS register.</td></tr></table>
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<h2 id="instruction-operand-encoding">Instruction Operand Encoding<a class="anchor" href="#instruction-operand-encoding">
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¶
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</a></h2>
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<table>
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<tr>
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<th>Op/En</th>
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<th>Operand 1</th>
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<th>Operand 2</th>
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<th>Operand 3</th>
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<th>Operand 4</th></tr>
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<tr>
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<td>ZO</td>
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<td>N/A</td>
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<td>N/A</td>
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<td>N/A</td>
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<td>N/A</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>Clears the AC flag bit in EFLAGS register. This disables any alignment checking of user-mode data accesses. Ifthe SMAP bit is set in the CR4 register, this disallows explicit supervisor-mode data accesses to user-mode pages.</p>
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<p>This instruction's operation is the same in non-64-bit modes and 64-bit mode. Attempts to execute CLAC when CPL > 0 cause #UD.</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>EFLAGS.AC := 0;
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</pre>
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<h2 id="flags-affected">Flags Affected<a class="anchor" href="#flags-affected">
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¶
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</a></h2>
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<p>AC cleared. Other flags are unaffected.</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="3">#UD</td>
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<td>If the LOCK prefix is used.</td></tr>
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<tr>
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<td>If the CPL > 0.</td></tr>
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<tr>
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<td>If CPUID.(EAX=07H, ECX=0H):EBX.SMAP[bit 20] = 0.</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 rowspan="2">#UD</td>
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<td>If the LOCK prefix is used.</td></tr>
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<tr>
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<td>If CPUID.(EAX=07H, ECX=0H):EBX.SMAP[bit 20] = 0.</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>#UD</td>
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<td>The CLAC instruction is not recognized in virtual-8086 mode.</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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<table>
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<tr>
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<td rowspan="3">#UD</td>
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<td>If the LOCK prefix is used.</td></tr>
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<tr>
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<td>If the CPL > 0.</td></tr>
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<tr>
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<td>If CPUID.(EAX=07H, ECX=0H):EBX.SMAP[bit 20] = 0.</td></tr></table>
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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 rowspan="3">#UD</td>
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<td>If the LOCK prefix is used.</td></tr>
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<tr>
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<td>If the CPL > 0.</td></tr>
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<tr>
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<td>If CPUID.(EAX=07H, ECX=0H):EBX.SMAP[bit 20] = 0.</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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