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| <h2 class="chapter">8 Object Attributes</h2> |
| |
| <p><a name="index-object-attributes-505"></a> |
| <samp><span class="command">as</span></samp> assembles source files written for a specific architecture |
| into object files for that architecture. But not all object files are alike. |
| Many architectures support incompatible variations. For instance, floating |
| point arguments might be passed in floating point registers if the object file |
| requires hardware floating point support—or floating point arguments might be |
| passed in integer registers if the object file supports processors with no |
| hardware floating point unit. Or, if two objects are built for different |
| generations of the same architecture, the combination may require the |
| newer generation at run-time. |
| |
| <p>This information is useful during and after linking. At link time, |
| <samp><span class="command">ld</span></samp> can warn about incompatible object files. After link |
| time, tools like <samp><span class="command">gdb</span></samp> can use it to process the linked file |
| correctly. |
| |
| <p>Compatibility information is recorded as a series of object attributes. Each |
| attribute has a <dfn>vendor</dfn>, <dfn>tag</dfn>, and <dfn>value</dfn>. The vendor is a |
| string, and indicates who sets the meaning of the tag. The tag is an integer, |
| and indicates what property the attribute describes. The value may be a string |
| or an integer, and indicates how the property affects this object. Missing |
| attributes are the same as attributes with a zero value or empty string value. |
| |
| <p>Object attributes were developed as part of the ABI for the ARM Architecture. |
| The file format is documented in <cite>ELF for the ARM Architecture</cite>. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="GNU-Object-Attributes.html#GNU-Object-Attributes">GNU Object Attributes</a>: <span class="sc">gnu</span> Object Attributes |
| <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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