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<h4 class="subsection">3.6.5 Output Section Data</h4>
<p><a name="index-data-447"></a><a name="index-section-data-448"></a><a name="index-output-section-data-449"></a><a name="index-BYTE_0028_0040var_007bexpression_007d_0029-450"></a><a name="index-SHORT_0028_0040var_007bexpression_007d_0029-451"></a><a name="index-LONG_0028_0040var_007bexpression_007d_0029-452"></a><a name="index-QUAD_0028_0040var_007bexpression_007d_0029-453"></a><a name="index-SQUAD_0028_0040var_007bexpression_007d_0029-454"></a>You can include explicit bytes of data in an output section by using
<code>BYTE</code>, <code>SHORT</code>, <code>LONG</code>, <code>QUAD</code>, or <code>SQUAD</code> as
an output section command. Each keyword is followed by an expression in
parentheses providing the value to store (see <a href="Expressions.html#Expressions">Expressions</a>). The
value of the expression is stored at the current value of the location
counter.
<p>The <code>BYTE</code>, <code>SHORT</code>, <code>LONG</code>, and <code>QUAD</code> commands
store one, two, four, and eight bytes (respectively). After storing the
bytes, the location counter is incremented by the number of bytes
stored.
<p>For example, this will store the byte 1 followed by the four byte value
of the symbol ‘<samp><span class="samp">addr</span></samp>’:
<pre class="smallexample"> BYTE(1)
LONG(addr)
</pre>
<p>When using a 64 bit host or target, <code>QUAD</code> and <code>SQUAD</code> are the
same; they both store an 8 byte, or 64 bit, value. When both host and
target are 32 bits, an expression is computed as 32 bits. In this case
<code>QUAD</code> stores a 32 bit value zero extended to 64 bits, and
<code>SQUAD</code> stores a 32 bit value sign extended to 64 bits.
<p>If the object file format of the output file has an explicit endianness,
which is the normal case, the value will be stored in that endianness.
When the object file format does not have an explicit endianness, as is
true of, for example, S-records, the value will be stored in the
endianness of the first input object file.
<p>Note—these commands only work inside a section description and not
between them, so the following will produce an error from the linker:
<pre class="smallexample"> SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } }</pre>
<p>whereas this will work:
<pre class="smallexample"> SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } }</pre>
<p><a name="index-FILL_0028_0040var_007bexpression_007d_0029-455"></a><a name="index-holes_002c-filling-456"></a><a name="index-unspecified-memory-457"></a>You may use the <code>FILL</code> command to set the fill pattern for the
current section. It is followed by an expression in parentheses. Any
otherwise unspecified regions of memory within the section (for example,
gaps left due to the required alignment of input sections) are filled
with the value of the expression, repeated as
necessary. A <code>FILL</code> statement covers memory locations after the
point at which it occurs in the section definition; by including more
than one <code>FILL</code> statement, you can have different fill patterns in
different parts of an output section.
<p>This example shows how to fill unspecified regions of memory with the
value ‘<samp><span class="samp">0x90</span></samp>’:
<pre class="smallexample"> FILL(0x90909090)
</pre>
<p>The <code>FILL</code> command is similar to the ‘<samp><span class="samp">=</span><var>fillexp</var></samp>’ output
section attribute, but it only affects the
part of the section following the <code>FILL</code> command, rather than the
entire section. If both are used, the <code>FILL</code> command takes
precedence. See <a href="Output-Section-Fill.html#Output-Section-Fill">Output Section Fill</a>, for details on the fill
expression.
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