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| <h4 class="subsection">9.13.15 Specifying CPU Architecture</h4> |
| |
| <p><a name="index-arch-directive_002c-i386-990"></a><a name="index-i386-arch-directive-991"></a><a name="index-arch-directive_002c-x86_002d64-992"></a><a name="index-x86_002d64-arch-directive-993"></a> |
| <code>as</code> may be told to assemble for a particular CPU |
| (sub-)architecture with the <code>.arch </code><var>cpu_type</var> directive. This |
| directive enables a warning when gas detects an instruction that is not |
| supported on the CPU specified. The choices for <var>cpu_type</var> are: |
| |
| <p><table summary=""><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">i8086</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">i186</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">i286</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">i386</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">i486</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">i586</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">i686</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">pentium</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">pentiumpro</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">pentiumii</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">pentiumiii</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">pentium4</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">prescott</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">nocona</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">core</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">core2</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">corei7</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">l1om</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">k6</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">k6_2</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">athlon</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">k8</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">amdfam10</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">bdver1</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">generic32</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">generic64</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.mmx</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse2</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse3</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.ssse3</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse4.1</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse4.2</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse4</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.avx</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.vmx</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.smx</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.ept</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.clflush</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.movbe</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.xsave</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.xsaveopt</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.aes</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.pclmul</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.fma</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.fsgsbase</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.rdrnd</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.f16c</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.3dnow</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.3dnowa</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse4a</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.sse5</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.syscall</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.rdtscp</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.svme</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.abm</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.lwp</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.fma4</span></samp>’ </td><td valign="top" width="20%">‘<samp><span class="samp">.xop</span></samp>’ |
| <br></td></tr><tr align="left"><td valign="top" width="20%">‘<samp><span class="samp">.padlock</span></samp>’ |
| <br></td></tr></table> |
| |
| <p>Apart from the warning, there are only two other effects on |
| <code>as</code> operation; Firstly, if you specify a CPU other than |
| ‘<samp><span class="samp">i486</span></samp>’, then shift by one instructions such as ‘<samp><span class="samp">sarl $1, %eax</span></samp>’ |
| will automatically use a two byte opcode sequence. The larger three |
| byte opcode sequence is used on the 486 (and when no architecture is |
| specified) because it executes faster on the 486. Note that you can |
| explicitly request the two byte opcode by writing ‘<samp><span class="samp">sarl %eax</span></samp>’. |
| Secondly, if you specify ‘<samp><span class="samp">i8086</span></samp>’, ‘<samp><span class="samp">i186</span></samp>’, or ‘<samp><span class="samp">i286</span></samp>’, |
| <em>and</em> ‘<samp><span class="samp">.code16</span></samp>’ or ‘<samp><span class="samp">.code16gcc</span></samp>’ then byte offset |
| conditional jumps will be promoted when necessary to a two instruction |
| sequence consisting of a conditional jump of the opposite sense around |
| an unconditional jump to the target. |
| |
| <p>Following the CPU architecture (but not a sub-architecture, which are those |
| starting with a dot), you may specify ‘<samp><span class="samp">jumps</span></samp>’ or ‘<samp><span class="samp">nojumps</span></samp>’ to |
| control automatic promotion of conditional jumps. ‘<samp><span class="samp">jumps</span></samp>’ is the |
| default, and enables jump promotion; All external jumps will be of the long |
| variety, and file-local jumps will be promoted as necessary. |
| (see <a href="i386_002dJumps.html#i386_002dJumps">i386-Jumps</a>) ‘<samp><span class="samp">nojumps</span></samp>’ leaves external conditional jumps as |
| byte offset jumps, and warns about file-local conditional jumps that |
| <code>as</code> promotes. |
| Unconditional jumps are treated as for ‘<samp><span class="samp">jumps</span></samp>’. |
| |
| <p>For example |
| |
| <pre class="smallexample"> .arch i8086,nojumps |
| </pre> |
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