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82 lines
3.9 KiB
HTML
82 lines
3.9 KiB
HTML
4 years ago
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<html lang="en">
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<title>Object Attributes - Using as</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="Using as">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="prev" href="Pseudo-Ops.html#Pseudo-Ops" title="Pseudo Ops">
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<link rel="next" href="Machine-Dependencies.html#Machine-Dependencies" title="Machine Dependencies">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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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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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled ``GNU Free Documentation License''.
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<style type="text/css"><!--
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Object-Attributes"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Machine-Dependencies.html#Machine-Dependencies">Machine Dependencies</a>,
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Previous: <a rel="previous" accesskey="p" href="Pseudo-Ops.html#Pseudo-Ops">Pseudo Ops</a>,
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Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
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<hr>
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</div>
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<h2 class="chapter">8 Object Attributes</h2>
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<p><a name="index-object-attributes-520"></a>
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<samp><span class="command">as</span></samp> assembles source files written for a specific architecture
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into object files for that architecture. But not all object files are alike.
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Many architectures support incompatible variations. For instance, floating
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point arguments might be passed in floating point registers if the object file
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requires hardware floating point support—or floating point arguments might be
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passed in integer registers if the object file supports processors with no
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hardware floating point unit. Or, if two objects are built for different
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generations of the same architecture, the combination may require the
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newer generation at run-time.
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<p>This information is useful during and after linking. At link time,
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<samp><span class="command">ld</span></samp> can warn about incompatible object files. After link
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time, tools like <samp><span class="command">gdb</span></samp> can use it to process the linked file
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correctly.
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<p>Compatibility information is recorded as a series of object attributes. Each
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attribute has a <dfn>vendor</dfn>, <dfn>tag</dfn>, and <dfn>value</dfn>. The vendor is a
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string, and indicates who sets the meaning of the tag. The tag is an integer,
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and indicates what property the attribute describes. The value may be a string
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or an integer, and indicates how the property affects this object. Missing
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attributes are the same as attributes with a zero value or empty string value.
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<p>Object attributes were developed as part of the ABI for the ARM Architecture.
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The file format is documented in <cite>ELF for the ARM Architecture</cite>.
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<ul class="menu">
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<li><a accesskey="1" href="GNU-Object-Attributes.html#GNU-Object-Attributes">GNU Object Attributes</a>: <span class="sc">gnu</span> Object Attributes
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<li><a accesskey="2" href="Defining-New-Object-Attributes.html#Defining-New-Object-Attributes">Defining New Object Attributes</a>: Defining New Object Attributes
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</ul>
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</body></html>
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