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| <title>LD: Output Section Data</title> |
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| <p> |
| Next: <a href="Output-Section-Keywords.html#Output-Section-Keywords" accesskey="n" rel="next">Output Section Keywords</a>, Previous: <a href="Input-Section.html#Input-Section" accesskey="p" rel="prev">Input Section</a>, Up: <a href="SECTIONS.html#SECTIONS" accesskey="u" rel="up">SECTIONS</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p> |
| </div> |
| <hr> |
| <a name="Output-Section-Data-1"></a> |
| <h4 class="subsection">3.6.5 Output Section Data</h4> |
| <a name="index-data"></a> |
| <a name="index-section-data"></a> |
| <a name="index-output-section-data"></a> |
| <a name="index-BYTE_0028expression_0029"></a> |
| <a name="index-SHORT_0028expression_0029"></a> |
| <a name="index-LONG_0028expression_0029"></a> |
| <a name="index-QUAD_0028expression_0029"></a> |
| <a name="index-SQUAD_0028expression_0029"></a> |
| <p>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> |
| <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> |
| <p>For example, this will store the byte 1 followed by the four byte value |
| of the symbol ‘<samp>addr</samp>’: |
| </p><div class="smallexample"> |
| <pre class="smallexample">BYTE(1) |
| LONG(addr) |
| </pre></div> |
| |
| <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> |
| <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> |
| <p>Note—these commands only work inside a section description and not |
| between them, so the following will produce an error from the linker: |
| </p><div class="smallexample"> |
| <pre class="smallexample">SECTIONS { .text : { *(.text) } LONG(1) .data : { *(.data) } } </pre></div> |
| <p>whereas this will work: |
| </p><div class="smallexample"> |
| <pre class="smallexample">SECTIONS { .text : { *(.text) ; LONG(1) } .data : { *(.data) } } </pre></div> |
| |
| <a name="index-FILL_0028expression_0029"></a> |
| <a name="index-holes_002c-filling"></a> |
| <a name="index-unspecified-memory"></a> |
| <p>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> |
| <p>This example shows how to fill unspecified regions of memory with the |
| value ‘<samp>0x90</samp>’: |
| </p><div class="smallexample"> |
| <pre class="smallexample">FILL(0x90909090) |
| </pre></div> |
| |
| <p>The <code>FILL</code> command is similar to the ‘<samp>=<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. |
| </p> |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Output-Section-Keywords.html#Output-Section-Keywords" accesskey="n" rel="next">Output Section Keywords</a>, Previous: <a href="Input-Section.html#Input-Section" accesskey="p" rel="prev">Input Section</a>, Up: <a href="SECTIONS.html#SECTIONS" accesskey="u" rel="up">SECTIONS</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="LD-Index.html#LD-Index" title="Index" rel="index">Index</a>]</p> |
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