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<title>MMIX-Opts - Using as</title>
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This file documents the GNU Assembler "as".
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Copyright (C) 1991-2015 Free Software Foundation, Inc.
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<a name="MMIX-Opts"></a>
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<a name="MMIX_002dOpts"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="MMIX_002dExpand.html#MMIX_002dExpand">MMIX-Expand</a>,
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Up: <a rel="up" accesskey="u" href="MMIX_002dDependent.html#MMIX_002dDependent">MMIX-Dependent</a>
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<h4 class="subsection">9.28.1 Command-line Options</h4>
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<p><a name="index-options_002c-MMIX-1559"></a><a name="index-MMIX-options-1560"></a>The MMIX version of <code>as</code> has some machine-dependent options.
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<p><a name="index-g_t_0040samp_007b_002d_002dfixed_002dspecial_002dregister_002dnames_007d-command-line-option_002c-MMIX-1561"></a>When ‘<samp><span class="samp">--fixed-special-register-names</span></samp>’ is specified, only the register
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names specified in <a href="MMIX_002dRegs.html#MMIX_002dRegs">MMIX-Regs</a> are recognized in the instructions
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<code>PUT</code> and <code>GET</code>.
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<p><a name="index-g_t_0040samp_007b_002d_002dglobalize_002dsymbols_007d-command-line-option_002c-MMIX-1562"></a>You can use the ‘<samp><span class="samp">--globalize-symbols</span></samp>’ to make all symbols global.
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This option is useful when splitting up a <code>mmixal</code> program into
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several files.
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<p><a name="index-g_t_0040samp_007b_002d_002dgnu_002dsyntax_007d-command-line-option_002c-MMIX-1563"></a>The ‘<samp><span class="samp">--gnu-syntax</span></samp>’ turns off most syntax compatibility with
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<code>mmixal</code>. Its usability is currently doubtful.
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<p><a name="index-g_t_0040samp_007b_002d_002drelax_007d-command-line-option_002c-MMIX-1564"></a>The ‘<samp><span class="samp">--relax</span></samp>’ option is not fully supported, but will eventually make
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the object file prepared for linker relaxation.
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<p><a name="index-g_t_0040samp_007b_002d_002dno_002dpredefined_002dsyms_007d-command-line-option_002c-MMIX-1565"></a>If you want to avoid inadvertently calling a predefined symbol and would
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rather get an error, for example when using <code>as</code> with a
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compiler or other machine-generated code, specify
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‘<samp><span class="samp">--no-predefined-syms</span></samp>’. This turns off built-in predefined
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definitions of all such symbols, including rounding-mode symbols, segment
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symbols, ‘<samp><span class="samp">BIT</span></samp>’ symbols, and <code>TRAP</code> symbols used in <code>mmix</code>
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“system calls”. It also turns off predefined special-register names,
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except when used in <code>PUT</code> and <code>GET</code> instructions.
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<p><a name="index-g_t_0040samp_007b_002d_002dno_002dexpand_007d-command-line-option_002c-MMIX-1566"></a>By default, some instructions are expanded to fit the size of the operand
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or an external symbol (see <a href="MMIX_002dExpand.html#MMIX_002dExpand">MMIX-Expand</a>). By passing
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‘<samp><span class="samp">--no-expand</span></samp>’, no such expansion will be done, instead causing errors
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at link time if the operand does not fit.
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<p><a name="index-g_t_0040samp_007b_002d_002dno_002dmerge_002dgregs_007d-command-line-option_002c-MMIX-1567"></a>The <code>mmixal</code> documentation (see <a href="mmixsite.html#mmixsite">mmixsite</a>) specifies that global
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registers allocated with the ‘<samp><span class="samp">GREG</span></samp>’ directive (see <a href="MMIX_002dgreg.html#MMIX_002dgreg">MMIX-greg</a>) and
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initialized to the same non-zero value, will refer to the same global
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register. This isn't strictly enforceable in <code>as</code> since the
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final addresses aren't known until link-time, but it will do an effort
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unless the ‘<samp><span class="samp">--no-merge-gregs</span></samp>’ option is specified. (Register merging
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isn't yet implemented in <code>ld</code>.)
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<p><a name="index-g_t_0040samp_007b_002dx_007d-command-line-option_002c-MMIX-1568"></a><code>as</code> will warn every time it expands an instruction to fit an
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operand unless the option ‘<samp><span class="samp">-x</span></samp>’ is specified. It is believed that
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this behaviour is more useful than just mimicking <code>mmixal</code>'s
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behaviour, in which instructions are only expanded if the ‘<samp><span class="samp">-x</span></samp>’ option
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is specified, and assembly fails otherwise, when an instruction needs to
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be expanded. It needs to be kept in mind that <code>mmixal</code> is both an
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assembler and linker, while <code>as</code> will expand instructions
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that at link stage can be contracted. (Though linker relaxation isn't yet
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implemented in <code>ld</code>.) The option ‘<samp><span class="samp">-x</span></samp>’ also imples
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‘<samp><span class="samp">--linker-allocated-gregs</span></samp>’.
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<p><a name="index-g_t_0040samp_007b_002d_002dno_002dpushj_002dstubs_007d-command-line-option_002c-MMIX-1569"></a><a name="index-g_t_0040samp_007b_002d_002dno_002dstubs_007d-command-line-option_002c-MMIX-1570"></a>If instruction expansion is enabled, <code>as</code> can expand a
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‘<samp><span class="samp">PUSHJ</span></samp>’ instruction into a series of instructions. The shortest
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expansion is to not expand it, but just mark the call as redirectable to a
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stub, which <code>ld</code> creates at link-time, but only if the
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original ‘<samp><span class="samp">PUSHJ</span></samp>’ instruction is found not to reach the target. The
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stub consists of the necessary instructions to form a jump to the target.
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This happens if <code>as</code> can assert that the ‘<samp><span class="samp">PUSHJ</span></samp>’
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instruction can reach such a stub. The option ‘<samp><span class="samp">--no-pushj-stubs</span></samp>’
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disables this shorter expansion, and the longer series of instructions is
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then created at assembly-time. The option ‘<samp><span class="samp">--no-stubs</span></samp>’ is a synonym,
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intended for compatibility with future releases, where generation of stubs
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for other instructions may be implemented.
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<p><a name="index-g_t_0040samp_007b_002d_002dlinker_002dallocated_002dgregs_007d-command-line-option_002c-MMIX-1571"></a>Usually a two-operand-expression (see <a href="GREG_002dbase.html#GREG_002dbase">GREG-base</a>) without a matching
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‘<samp><span class="samp">GREG</span></samp>’ directive is treated as an error by <code>as</code>. When
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the option ‘<samp><span class="samp">--linker-allocated-gregs</span></samp>’ is in effect, they are instead
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passed through to the linker, which will allocate as many global registers
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as is needed.
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