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<title>ESA/390 Syntax - 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="ESA%2f390-Syntax"></a>
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<a name="ESA_002f390-Syntax"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="ESA_002f390-Floating-Point.html#ESA_002f390-Floating-Point">ESA/390 Floating Point</a>,
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Previous: <a rel="previous" accesskey="p" href="ESA_002f390-Options.html#ESA_002f390-Options">ESA/390 Options</a>,
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Up: <a rel="up" accesskey="u" href="ESA_002f390_002dDependent.html#ESA_002f390_002dDependent">ESA/390-Dependent</a>
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<h4 class="subsection">9.14.3 Syntax</h4>
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<p>The opcode/operand syntax follows the ESA/390 Principles of Operation
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manual; assembler directives and general syntax are loosely based on the
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prevailing AT&T/SVR4/ELF/Solaris style notation. HLASM-style directives
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are <em>not</em> supported for the most part, with the exception of those
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described herein.
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<p>A leading dot in front of directives is optional, and the case of
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directives is ignored; thus for example, .using and USING have the same
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effect.
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<p>A colon may immediately follow a label definition. This is
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simply for compatibility with how most assembly language programmers
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write code.
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<p>‘<samp><span class="samp">#</span></samp>’ is the line comment character.
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<p>‘<samp><span class="samp">;</span></samp>’ can be used instead of a newline to separate statements.
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<p>Since ‘<samp><span class="samp">$</span></samp>’ has no special meaning, you may use it in symbol names.
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<p>Registers can be given the symbolic names r0..r15, fp0, fp2, fp4, fp6.
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By using thesse symbolic names, <code>as</code> can detect simple
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syntax errors. The name rarg or r.arg is a synonym for r11, rtca or r.tca
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for r12, sp, r.sp, dsa r.dsa for r13, lr or r.lr for r14, rbase or r.base
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for r3 and rpgt or r.pgt for r4.
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<p>‘<samp><span class="samp">*</span></samp>’ is the current location counter. Unlike ‘<samp><span class="samp">.</span></samp>’ it is always
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relative to the last USING directive. Note that this means that
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expressions cannot use multiplication, as any occurrence of ‘<samp><span class="samp">*</span></samp>’
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will be interpreted as a location counter.
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<p>All labels are relative to the last USING. Thus, branches to a label
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always imply the use of base+displacement.
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<p>Many of the usual forms of address constants / address literals
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are supported. Thus,
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<pre class="example"> .using *,r3
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L r15,=A(some_routine)
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LM r6,r7,=V(some_longlong_extern)
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A r1,=F'12'
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AH r0,=H'42'
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ME r6,=E'3.1416'
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MD r6,=D'3.14159265358979'
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O r6,=XL4'cacad0d0'
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.ltorg
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</pre>
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<p>should all behave as expected: that is, an entry in the literal
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pool will be created (or reused if it already exists), and the
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instruction operands will be the displacement into the literal pool
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using the current base register (as last declared with the <code>.using</code>
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directive).
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