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| <h4 class="subsection">9.12.3 Syntax</h4> |
| |
| <p>The opcode/operand syntax follows the ESA/390 Principles of Operation |
| manual; assembler directives and general syntax are loosely based on the |
| prevailing AT&T/SVR4/ELF/Solaris style notation. HLASM-style directives |
| are <em>not</em> supported for the most part, with the exception of those |
| described herein. |
| |
| <p>A leading dot in front of directives is optional, and the case of |
| directives is ignored; thus for example, .using and USING have the same |
| effect. |
| |
| <p>A colon may immediately follow a label definition. This is |
| simply for compatibility with how most assembly language programmers |
| write code. |
| |
| <p>‘<samp><span class="samp">#</span></samp>’ is the line comment character. |
| |
| <p>‘<samp><span class="samp">;</span></samp>’ can be used instead of a newline to separate statements. |
| |
| <p>Since ‘<samp><span class="samp">$</span></samp>’ has no special meaning, you may use it in symbol names. |
| |
| <p>Registers can be given the symbolic names r0..r15, fp0, fp2, fp4, fp6. |
| By using thesse symbolic names, <code>as</code> can detect simple |
| syntax errors. The name rarg or r.arg is a synonym for r11, rtca or r.tca |
| for r12, sp, r.sp, dsa r.dsa for r13, lr or r.lr for r14, rbase or r.base |
| for r3 and rpgt or r.pgt for r4. |
| |
| <p>‘<samp><span class="samp">*</span></samp>’ is the current location counter. Unlike ‘<samp><span class="samp">.</span></samp>’ it is always |
| relative to the last USING directive. Note that this means that |
| expressions cannot use multiplication, as any occurrence of ‘<samp><span class="samp">*</span></samp>’ |
| will be interpreted as a location counter. |
| |
| <p>All labels are relative to the last USING. Thus, branches to a label |
| always imply the use of base+displacement. |
| |
| <p>Many of the usual forms of address constants / address literals |
| are supported. Thus, |
| <pre class="example"> .using *,r3 |
| L r15,=A(some_routine) |
| LM r6,r7,=V(some_longlong_extern) |
| A r1,=F'12' |
| AH r0,=H'42' |
| ME r6,=E'3.1416' |
| MD r6,=D'3.14159265358979' |
| O r6,=XL4'cacad0d0' |
| .ltorg |
| </pre> |
| <p>should all behave as expected: that is, an entry in the literal |
| pool will be created (or reused if it already exists), and the |
| instruction operands will be the displacement into the literal pool |
| using the current base register (as last declared with the <code>.using</code> |
| directive). |
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