Object-Attributes.html 5.7 KB

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  60. Next: <a href="Machine-Dependencies.html#Machine-Dependencies" accesskey="n" rel="next">Machine Dependencies</a>, Previous: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="p" rel="prev">Pseudo Ops</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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  63. <a name="Object-Attributes-1"></a>
  64. <h2 class="chapter">8 Object Attributes</h2>
  65. <a name="index-object-attributes"></a>
  66. <p><code>as</code> assembles source files written for a specific architecture
  67. into object files for that architecture. But not all object files are alike.
  68. Many architectures support incompatible variations. For instance, floating
  69. point arguments might be passed in floating point registers if the object file
  70. requires hardware floating point support&mdash;or floating point arguments might be
  71. passed in integer registers if the object file supports processors with no
  72. hardware floating point unit. Or, if two objects are built for different
  73. generations of the same architecture, the combination may require the
  74. newer generation at run-time.
  75. </p>
  76. <p>This information is useful during and after linking. At link time,
  77. <code>ld</code> can warn about incompatible object files. After link
  78. time, tools like <code>gdb</code> can use it to process the linked file
  79. correctly.
  80. </p>
  81. <p>Compatibility information is recorded as a series of object attributes. Each
  82. attribute has a <em>vendor</em>, <em>tag</em>, and <em>value</em>. The vendor is a
  83. string, and indicates who sets the meaning of the tag. The tag is an integer,
  84. and indicates what property the attribute describes. The value may be a string
  85. or an integer, and indicates how the property affects this object. Missing
  86. attributes are the same as attributes with a zero value or empty string value.
  87. </p>
  88. <p>Object attributes were developed as part of the ABI for the ARM Architecture.
  89. The file format is documented in <cite>ELF for the ARM Architecture</cite>.
  90. </p>
  91. <table class="menu" border="0" cellspacing="0">
  92. <tr><td align="left" valign="top">&bull; <a href="GNU-Object-Attributes.html#GNU-Object-Attributes" accesskey="1">GNU Object Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top"><small>GNU</small> Object Attributes
  93. </td></tr>
  94. <tr><td align="left" valign="top">&bull; <a href="Defining-New-Object-Attributes.html#Defining-New-Object-Attributes" accesskey="2">Defining New Object Attributes</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">Defining New Object Attributes
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