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toolchain-gcc-arm-embedded/share/doc/gcc-arm-none-eabi/html/ld.html/Input-Section-Basics.html

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  1. <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

  2. <html>

  3. <!-- This file documents the GNU linker LD

  4. (GNU Arm Embedded Toolchain 10-2020-q4-major)

  5. version 2.35.1.

  6. 

  7. Copyright (C) 1991-2020 Free Software Foundation, Inc.

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  18. <title>Input Section Basics (LD)</title>

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  27. <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">

  28. <link href="Input-Section.html#Input-Section" rel="up" title="Input Section">

  29. <link href="Input-Section-Wildcards.html#Input-Section-Wildcards" rel="next" title="Input Section Wildcards">

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  62. <body lang="en">

  63. <a name="Input-Section-Basics"></a>

  64. <div class="header">

  65. <p>

  66. Next: <a href="Input-Section-Wildcards.html#Input-Section-Wildcards" accesskey="n" rel="next">Input Section Wildcards</a>, Up: <a href="Input-Section.html#Input-Section" accesskey="u" rel="up">Input Section</a> &nbsp; [<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>

  67. </div>

  68. <hr>

  69. <a name="Input-Section-Basics-1"></a>

  70. <h4 class="subsubsection">3.6.4.1 Input Section Basics</h4>

  71. <a name="index-input-section-basics"></a>

  72. <p>An input section description consists of a file name optionally followed

  73. by a list of section names in parentheses.

  74. </p>

  75. <p>The file name and the section name may be wildcard patterns, which we

  76. describe further below (see <a href="Input-Section-Wildcards.html#Input-Section-Wildcards">Input Section Wildcards</a>).

  77. </p>

  78. <p>The most common input section description is to include all input

  79. sections with a particular name in the output section.  For example, to

  80. include all input &lsquo;<samp>.text</samp>&rsquo; sections, you would write:

  81. </p><div class="smallexample">

  82. <pre class="smallexample">*(.text)

  83. </pre></div>

  84. <p>Here the &lsquo;<samp>*</samp>&rsquo; is a wildcard which matches any file name.  To exclude a list

  85. <a name="index-EXCLUDE_005fFILE"></a>

  86. of files from matching the file name wildcard, EXCLUDE_FILE may be used to

  87. match all files except the ones specified in the EXCLUDE_FILE list.  For

  88. example:

  89. </p><div class="smallexample">

  90. <pre class="smallexample">EXCLUDE_FILE (*crtend.o *otherfile.o) *(.ctors)

  91. </pre></div>

  92. <p>will cause all .ctors sections from all files except <samp>crtend.o</samp>

  93. and <samp>otherfile.o</samp> to be included.  The EXCLUDE_FILE can also be

  94. placed inside the section list, for example:

  95. </p><div class="smallexample">

  96. <pre class="smallexample">*(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors)

  97. </pre></div>

  98. <p>The result of this is identically to the previous example.  Supporting

  99. two syntaxes for EXCLUDE_FILE is useful if the section list contains

  100. more than one section, as described below.

  101. </p>

  102. <p>There are two ways to include more than one section:

  103. </p><div class="smallexample">

  104. <pre class="smallexample">*(.text .rdata)

  105. *(.text) *(.rdata)

  106. </pre></div>

  107. <p>The difference between these is the order in which the &lsquo;<samp>.text</samp>&rsquo; and

  108. &lsquo;<samp>.rdata</samp>&rsquo; input sections will appear in the output section.  In the

  109. first example, they will be intermingled, appearing in the same order as

  110. they are found in the linker input.  In the second example, all

  111. &lsquo;<samp>.text</samp>&rsquo; input sections will appear first, followed by all

  112. &lsquo;<samp>.rdata</samp>&rsquo; input sections.

  113. </p>

  114. <p>When using EXCLUDE_FILE with more than one section, if the exclusion

  115. is within the section list then the exclusion only applies to the

  116. immediately following section, for example:

  117. </p><div class="smallexample">

  118. <pre class="smallexample">*(EXCLUDE_FILE (*somefile.o) .text .rdata)

  119. </pre></div>

  120. <p>will cause all &lsquo;<samp>.text</samp>&rsquo; sections from all files except

  121. <samp>somefile.o</samp> to be included, while all &lsquo;<samp>.rdata</samp>&rsquo; sections

  122. from all files, including <samp>somefile.o</samp>, will be included.  To

  123. exclude the &lsquo;<samp>.rdata</samp>&rsquo; sections from <samp>somefile.o</samp> the example

  124. could be modified to:

  125. </p><div class="smallexample">

  126. <pre class="smallexample">*(EXCLUDE_FILE (*somefile.o) .text EXCLUDE_FILE (*somefile.o) .rdata)

  127. </pre></div>

  128. <p>Alternatively, placing the EXCLUDE_FILE outside of the section list,

  129. before the input file selection, will cause the exclusion to apply for

  130. all sections.  Thus the previous example can be rewritten as:

  131. </p><div class="smallexample">

  132. <pre class="smallexample">EXCLUDE_FILE (*somefile.o) *(.text .rdata)

  133. </pre></div>

  134. 

  135. <p>You can specify a file name to include sections from a particular file.

  136. You would do this if one or more of your files contain special data that

  137. needs to be at a particular location in memory.  For example:

  138. </p><div class="smallexample">

  139. <pre class="smallexample">data.o(.data)

  140. </pre></div>

  141. 

  142. <p>To refine the sections that are included based on the section flags

  143. of an input section, INPUT_SECTION_FLAGS may be used.

  144. </p>

  145. <p>Here is a simple example for using Section header flags for ELF sections:

  146. </p>

  147. <div class="smallexample">

  148. <pre class="smallexample">SECTIONS {

  149.   .text : { INPUT_SECTION_FLAGS (SHF_MERGE &amp; SHF_STRINGS) *(.text) }

  150.   .text2 :  { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) }

  151. }

  152. </pre></div>

  153. 

  154. <p>In this example, the output section &lsquo;<samp>.text</samp>&rsquo; will be comprised of any

  155. input section matching the name *(.text) whose section header flags

  156. <code>SHF_MERGE</code> and <code>SHF_STRINGS</code> are set.  The output section

  157. &lsquo;<samp>.text2</samp>&rsquo; will be comprised of any input section matching the name *(.text)

  158. whose section header flag <code>SHF_WRITE</code> is clear.

  159. </p>

  160. <p>You can also specify files within archives by writing a pattern

  161. matching the archive, a colon, then the pattern matching the file,

  162. with no whitespace around the colon.

  163. </p>

  164. <dl compact="compact">

  165. <dt>&lsquo;<samp>archive:file</samp>&rsquo;</dt>

  166. <dd><p>matches file within archive

  167. </p></dd>

  168. <dt>&lsquo;<samp>archive:</samp>&rsquo;</dt>

  169. <dd><p>matches the whole archive

  170. </p></dd>

  171. <dt>&lsquo;<samp>:file</samp>&rsquo;</dt>

  172. <dd><p>matches file but not one in an archive

  173. </p></dd>

  174. </dl>

  175. 

  176. <p>Either one or both of &lsquo;<samp>archive</samp>&rsquo; and &lsquo;<samp>file</samp>&rsquo; can contain shell

  177. wildcards.  On DOS based file systems, the linker will assume that a

  178. single letter followed by a colon is a drive specifier, so

  179. &lsquo;<samp>c:myfile.o</samp>&rsquo; is a simple file specification, not &lsquo;<samp>myfile.o</samp>&rsquo;

  180. within an archive called &lsquo;<samp>c</samp>&rsquo;.  &lsquo;<samp>archive:file</samp>&rsquo; filespecs may

  181. also be used within an <code>EXCLUDE_FILE</code> list, but may not appear in

  182. other linker script contexts.  For instance, you cannot extract a file

  183. from an archive by using &lsquo;<samp>archive:file</samp>&rsquo; in an <code>INPUT</code>

  184. command.

  185. </p>

  186. <p>If you use a file name without a list of sections, then all sections in

  187. the input file will be included in the output section.  This is not

  188. commonly done, but it may by useful on occasion.  For example:

  189. </p><div class="smallexample">

  190. <pre class="smallexample">data.o

  191. </pre></div>

  192. 

  193. <p>When you use a file name which is not an &lsquo;<samp>archive:file</samp>&rsquo; specifier

  194. and does not contain any wild card

  195. characters, the linker will first see if you also specified the file

  196. name on the linker command line or in an <code>INPUT</code> command.  If you

  197. did not, the linker will attempt to open the file as an input file, as

  198. though it appeared on the command line.  Note that this differs from an

  199. <code>INPUT</code> command, because the linker will not search for the file in

  200. the archive search path.

  201. </p>

  202. <hr>

  203. <div class="header">

  204. <p>

  205. Next: <a href="Input-Section-Wildcards.html#Input-Section-Wildcards" accesskey="n" rel="next">Input Section Wildcards</a>, Up: <a href="Input-Section.html#Input-Section" accesskey="u" rel="up">Input Section</a> &nbsp; [<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>

  206. </div>

  207. 

  208. 

  209. 

  210. </body>

  211. </html>