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113 lines
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<title>s390 Operand Modifier - 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="s390-Operand-Modifier"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="s390-Instruction-Marker.html#s390-Instruction-Marker">s390 Instruction Marker</a>,
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Previous: <a rel="previous" accesskey="p" href="s390-Aliases.html#s390-Aliases">s390 Aliases</a>,
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Up: <a rel="up" accesskey="u" href="s390-Syntax.html#s390-Syntax">s390 Syntax</a>
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<h5 class="subsubsection">9.38.3.6 Instruction Operand Modifier</h5>
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<p><a name="index-instruction-operand-modifier_002c-s390-1901"></a><a name="index-s390-instruction-operand-modifier-1902"></a>
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If a symbol modifier is attached to a symbol in an expression for an
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instruction operand field, the symbol term is replaced with a reference
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to an object in the global offset table (GOT) or the procedure linkage
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table (PLT). The following expressions are allowed:
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‘<samp><span class="samp">symbol@modifier + constant</span></samp>’,
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‘<samp><span class="samp">symbol@modifier + label + constant</span></samp>’, and
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‘<samp><span class="samp">symbol@modifier - label + constant</span></samp>’.
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The term ‘<samp><span class="samp">symbol</span></samp>’ is the symbol that will be entered into the GOT or
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PLT, ‘<samp><span class="samp">label</span></samp>’ is a local label, and ‘<samp><span class="samp">constant</span></samp>’ is an arbitrary
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expression that the assembler can evaluate to a constant value.
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<p>The term ‘<samp><span class="samp">(symbol + constant1)@modifier +/- label + constant2</span></samp>’
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is also accepted but a warning message is printed and the term is
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converted to ‘<samp><span class="samp">symbol@modifier +/- label + constant1 + constant2</span></samp>’.
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<dl>
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<dt><code>@got</code><dt><code>@got12</code><dd>The @got modifier can be used for displacement fields, 16-bit immediate
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fields and 32-bit pc-relative immediate fields. The @got12 modifier is
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synonym to @got. The symbol is added to the GOT. For displacement
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fields and 16-bit immediate fields the symbol term is replaced with
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the offset from the start of the GOT to the GOT slot for the symbol.
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For a 32-bit pc-relative field the pc-relative offset to the GOT
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slot from the current instruction address is used.
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<br><dt><code>@gotent</code><dd>The @gotent modifier can be used for 32-bit pc-relative immediate fields.
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The symbol is added to the GOT and the symbol term is replaced with
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the pc-relative offset from the current instruction to the GOT slot for the
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symbol.
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<br><dt><code>@gotoff</code><dd>The @gotoff modifier can be used for 16-bit immediate fields. The symbol
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term is replaced with the offset from the start of the GOT to the
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address of the symbol.
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<br><dt><code>@gotplt</code><dd>The @gotplt modifier can be used for displacement fields, 16-bit immediate
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fields, and 32-bit pc-relative immediate fields. A procedure linkage
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table entry is generated for the symbol and a jump slot for the symbol
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is added to the GOT. For displacement fields and 16-bit immediate
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fields the symbol term is replaced with the offset from the start of the
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GOT to the jump slot for the symbol. For a 32-bit pc-relative field
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the pc-relative offset to the jump slot from the current instruction
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address is used.
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<br><dt><code>@plt</code><dd>The @plt modifier can be used for 16-bit and 32-bit pc-relative immediate
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fields. A procedure linkage table entry is generated for the symbol.
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The symbol term is replaced with the relative offset from the current
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instruction to the PLT entry for the symbol.
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<br><dt><code>@pltoff</code><dd>The @pltoff modifier can be used for 16-bit immediate fields. The symbol
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term is replaced with the offset from the start of the PLT to the address
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of the symbol.
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<br><dt><code>@gotntpoff</code><dd>The @gotntpoff modifier can be used for displacement fields. The symbol
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is added to the static TLS block and the negated offset to the symbol
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in the static TLS block is added to the GOT. The symbol term is replaced
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with the offset to the GOT slot from the start of the GOT.
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<br><dt><code>@indntpoff</code><dd>The @indntpoff modifier can be used for 32-bit pc-relative immediate
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fields. The symbol is added to the static TLS block and the negated offset
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to the symbol in the static TLS block is added to the GOT. The symbol term
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is replaced with the pc-relative offset to the GOT slot from the current
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instruction address.
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</dl>
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<p>For more information about the thread local storage modifiers
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‘<samp><span class="samp">gotntpoff</span></samp>’ and ‘<samp><span class="samp">indntpoff</span></samp>’ see the ELF extension documentation
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‘<samp><span class="samp">ELF Handling For Thread-Local Storage</span></samp>’.
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