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<h2 class="chapter">8 Object Attributes</h2>
<p><a name="index-object-attributes-504"></a>
<span class="command">as</span> 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,
<span class="command">ld</span> can warn about incompatible object files. After link
time, tools like <span class="command">gdb</span> 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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