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| <h4 class="subsection">9.25.1 Command-line Options</h4> |
| |
| <p><a name="index-options_002c-MMIX-1312"></a><a name="index-MMIX-options-1313"></a>The MMIX version of <code>as</code> has some machine-dependent options. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dfixed_002dspecial_002dregister_002dnames_007d-command-line-option_002c-MMIX-1314"></a>When ‘<samp><span class="samp">--fixed-special-register-names</span></samp>’ is specified, only the register |
| names specified in <a href="MMIX_002dRegs.html#MMIX_002dRegs">MMIX-Regs</a> are recognized in the instructions |
| <code>PUT</code> and <code>GET</code>. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dglobalize_002dsymbols_007d-command-line-option_002c-MMIX-1315"></a>You can use the ‘<samp><span class="samp">--globalize-symbols</span></samp>’ to make all symbols global. |
| This option is useful when splitting up a <code>mmixal</code> program into |
| several files. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dgnu_002dsyntax_007d-command-line-option_002c-MMIX-1316"></a>The ‘<samp><span class="samp">--gnu-syntax</span></samp>’ turns off most syntax compatibility with |
| <code>mmixal</code>. Its usability is currently doubtful. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002drelax_007d-command-line-option_002c-MMIX-1317"></a>The ‘<samp><span class="samp">--relax</span></samp>’ option is not fully supported, but will eventually make |
| the object file prepared for linker relaxation. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dno_002dpredefined_002dsyms_007d-command-line-option_002c-MMIX-1318"></a>If you want to avoid inadvertently calling a predefined symbol and would |
| rather get an error, for example when using <code>as</code> with a |
| compiler or other machine-generated code, specify |
| ‘<samp><span class="samp">--no-predefined-syms</span></samp>’. This turns off built-in predefined |
| definitions of all such symbols, including rounding-mode symbols, segment |
| symbols, ‘<samp><span class="samp">BIT</span></samp>’ symbols, and <code>TRAP</code> symbols used in <code>mmix</code> |
| “system calls”. It also turns off predefined special-register names, |
| except when used in <code>PUT</code> and <code>GET</code> instructions. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dno_002dexpand_007d-command-line-option_002c-MMIX-1319"></a>By default, some instructions are expanded to fit the size of the operand |
| or an external symbol (see <a href="MMIX_002dExpand.html#MMIX_002dExpand">MMIX-Expand</a>). By passing |
| ‘<samp><span class="samp">--no-expand</span></samp>’, no such expansion will be done, instead causing errors |
| at link time if the operand does not fit. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dno_002dmerge_002dgregs_007d-command-line-option_002c-MMIX-1320"></a>The <code>mmixal</code> documentation (see <a href="mmixsite.html#mmixsite">mmixsite</a>) specifies that global |
| registers allocated with the ‘<samp><span class="samp">GREG</span></samp>’ directive (see <a href="MMIX_002dgreg.html#MMIX_002dgreg">MMIX-greg</a>) and |
| initialized to the same non-zero value, will refer to the same global |
| register. This isn't strictly enforceable in <code>as</code> since the |
| final addresses aren't known until link-time, but it will do an effort |
| unless the ‘<samp><span class="samp">--no-merge-gregs</span></samp>’ option is specified. (Register merging |
| isn't yet implemented in <code>ld</code>.) |
| |
| <p><a name="index-g_t_0040samp_007b_002dx_007d-command-line-option_002c-MMIX-1321"></a><code>as</code> will warn every time it expands an instruction to fit an |
| operand unless the option ‘<samp><span class="samp">-x</span></samp>’ is specified. It is believed that |
| this behaviour is more useful than just mimicking <code>mmixal</code>'s |
| behaviour, in which instructions are only expanded if the ‘<samp><span class="samp">-x</span></samp>’ option |
| is specified, and assembly fails otherwise, when an instruction needs to |
| be expanded. It needs to be kept in mind that <code>mmixal</code> is both an |
| assembler and linker, while <code>as</code> will expand instructions |
| that at link stage can be contracted. (Though linker relaxation isn't yet |
| implemented in <code>ld</code>.) The option ‘<samp><span class="samp">-x</span></samp>’ also imples |
| ‘<samp><span class="samp">--linker-allocated-gregs</span></samp>’. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dno_002dpushj_002dstubs_007d-command-line-option_002c-MMIX-1322"></a><a name="index-g_t_0040samp_007b_002d_002dno_002dstubs_007d-command-line-option_002c-MMIX-1323"></a>If instruction expansion is enabled, <code>as</code> can expand a |
| ‘<samp><span class="samp">PUSHJ</span></samp>’ instruction into a series of instructions. The shortest |
| expansion is to not expand it, but just mark the call as redirectable to a |
| stub, which <code>ld</code> creates at link-time, but only if the |
| original ‘<samp><span class="samp">PUSHJ</span></samp>’ instruction is found not to reach the target. The |
| stub consists of the necessary instructions to form a jump to the target. |
| This happens if <code>as</code> can assert that the ‘<samp><span class="samp">PUSHJ</span></samp>’ |
| instruction can reach such a stub. The option ‘<samp><span class="samp">--no-pushj-stubs</span></samp>’ |
| disables this shorter expansion, and the longer series of instructions is |
| then created at assembly-time. The option ‘<samp><span class="samp">--no-stubs</span></samp>’ is a synonym, |
| intended for compatibility with future releases, where generation of stubs |
| for other instructions may be implemented. |
| |
| <p><a name="index-g_t_0040samp_007b_002d_002dlinker_002dallocated_002dgregs_007d-command-line-option_002c-MMIX-1324"></a>Usually a two-operand-expression (see <a href="GREG_002dbase.html#GREG_002dbase">GREG-base</a>) without a matching |
| ‘<samp><span class="samp">GREG</span></samp>’ directive is treated as an error by <code>as</code>. When |
| the option ‘<samp><span class="samp">--linker-allocated-gregs</span></samp>’ is in effect, they are instead |
| passed through to the linker, which will allocate as many global registers |
| as is needed. |
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