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| <a name="Input-Section-Basics"></a> |
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| <h5 class="subsubsection">3.6.4.1 Input Section Basics</h5> |
| |
| <p><a name="index-input-section-basics-457"></a>An input section description consists of a file name optionally followed |
| by a list of section names in parentheses. |
| |
| <p>The file name and the section name may be wildcard patterns, which we |
| describe further below (see <a href="Input-Section-Wildcards.html#Input-Section-Wildcards">Input Section Wildcards</a>). |
| |
| <p>The most common input section description is to include all input |
| sections with a particular name in the output section. For example, to |
| include all input ‘<samp><span class="samp">.text</span></samp>’ sections, you would write: |
| <pre class="smallexample"> *(.text) |
| </pre> |
| <p class="noindent">Here the ‘<samp><span class="samp">*</span></samp>’ is a wildcard which matches any file name. To exclude a list |
| <a name="index-EXCLUDE_005fFILE-458"></a>of files from matching the file name wildcard, EXCLUDE_FILE may be used to |
| match all files except the ones specified in the EXCLUDE_FILE list. For |
| example: |
| <pre class="smallexample"> EXCLUDE_FILE (*crtend.o *otherfile.o) *(.ctors) |
| </pre> |
| <p class="noindent">will cause all .ctors sections from all files except <samp><span class="file">crtend.o</span></samp> |
| and <samp><span class="file">otherfile.o</span></samp> to be included. The EXCLUDE_FILE can also be |
| placed inside the section list, for example: |
| <pre class="smallexample"> *(EXCLUDE_FILE (*crtend.o *otherfile.o) .ctors) |
| </pre> |
| <p class="noindent">The result of this is identically to the previous example. Supporting |
| two syntaxes for EXCLUDE_FILE is useful if the section list contains |
| more than one section, as described below. |
| |
| <p>There are two ways to include more than one section: |
| <pre class="smallexample"> *(.text .rdata) |
| *(.text) *(.rdata) |
| </pre> |
| <p class="noindent">The difference between these is the order in which the ‘<samp><span class="samp">.text</span></samp>’ and |
| ‘<samp><span class="samp">.rdata</span></samp>’ input sections will appear in the output section. In the |
| first example, they will be intermingled, appearing in the same order as |
| they are found in the linker input. In the second example, all |
| ‘<samp><span class="samp">.text</span></samp>’ input sections will appear first, followed by all |
| ‘<samp><span class="samp">.rdata</span></samp>’ input sections. |
| |
| <p>When using EXCLUDE_FILE with more than one section, if the exclusion |
| is within the section list then the exclusion only applies to the |
| immediately following section, for example: |
| <pre class="smallexample"> *(EXCLUDE_FILE (*somefile.o) .text .rdata) |
| </pre> |
| <p class="noindent">will cause all ‘<samp><span class="samp">.text</span></samp>’ sections from all files except |
| <samp><span class="file">somefile.o</span></samp> to be included, while all ‘<samp><span class="samp">.rdata</span></samp>’ sections |
| from all files, including <samp><span class="file">somefile.o</span></samp>, will be included. To |
| exclude the ‘<samp><span class="samp">.rdata</span></samp>’ sections from <samp><span class="file">somefile.o</span></samp> the example |
| could be modified to: |
| <pre class="smallexample"> *(EXCLUDE_FILE (*somefile.o) .text EXCLUDE_FILE (*somefile.o) .rdata) |
| </pre> |
| <p class="noindent">Alternatively, placing the EXCLUDE_FILE outside of the section list, |
| before the input file selection, will cause the exclusion to apply for |
| all sections. Thus the previous example can be rewritten as: |
| <pre class="smallexample"> EXCLUDE_FILE (*somefile.o) *(.text .rdata) |
| </pre> |
| <p>You can specify a file name to include sections from a particular file. |
| You would do this if one or more of your files contain special data that |
| needs to be at a particular location in memory. For example: |
| <pre class="smallexample"> data.o(.data) |
| </pre> |
| <p>To refine the sections that are included based on the section flags |
| of an input section, INPUT_SECTION_FLAGS may be used. |
| |
| <p>Here is a simple example for using Section header flags for ELF sections: |
| |
| <pre class="smallexample"> SECTIONS { |
| .text : { INPUT_SECTION_FLAGS (SHF_MERGE & SHF_STRINGS) *(.text) } |
| .text2 : { INPUT_SECTION_FLAGS (!SHF_WRITE) *(.text) } |
| } |
| </pre> |
| <p>In this example, the output section ‘<samp><span class="samp">.text</span></samp>’ will be comprised of any |
| input section matching the name *(.text) whose section header flags |
| <code>SHF_MERGE</code> and <code>SHF_STRINGS</code> are set. The output section |
| ‘<samp><span class="samp">.text2</span></samp>’ will be comprised of any input section matching the name *(.text) |
| whose section header flag <code>SHF_WRITE</code> is clear. |
| |
| <p>You can also specify files within archives by writing a pattern |
| matching the archive, a colon, then the pattern matching the file, |
| with no whitespace around the colon. |
| |
| <dl> |
| <dt>‘<samp><span class="samp">archive:file</span></samp>’<dd>matches file within archive |
| <br><dt>‘<samp><span class="samp">archive:</span></samp>’<dd>matches the whole archive |
| <br><dt>‘<samp><span class="samp">:file</span></samp>’<dd>matches file but not one in an archive |
| </dl> |
| |
| <p>Either one or both of ‘<samp><span class="samp">archive</span></samp>’ and ‘<samp><span class="samp">file</span></samp>’ can contain shell |
| wildcards. On DOS based file systems, the linker will assume that a |
| single letter followed by a colon is a drive specifier, so |
| ‘<samp><span class="samp">c:myfile.o</span></samp>’ is a simple file specification, not ‘<samp><span class="samp">myfile.o</span></samp>’ |
| within an archive called ‘<samp><span class="samp">c</span></samp>’. ‘<samp><span class="samp">archive:file</span></samp>’ filespecs may |
| also be used within an <code>EXCLUDE_FILE</code> list, but may not appear in |
| other linker script contexts. For instance, you cannot extract a file |
| from an archive by using ‘<samp><span class="samp">archive:file</span></samp>’ in an <code>INPUT</code> |
| command. |
| |
| <p>If you use a file name without a list of sections, then all sections in |
| the input file will be included in the output section. This is not |
| commonly done, but it may by useful on occasion. For example: |
| <pre class="smallexample"> data.o |
| </pre> |
| <p>When you use a file name which is not an ‘<samp><span class="samp">archive:file</span></samp>’ specifier |
| and does not contain any wild card |
| characters, the linker will first see if you also specified the file |
| name on the linker command line or in an <code>INPUT</code> command. If you |
| did not, the linker will attempt to open the file as an input file, as |
| though it appeared on the command line. Note that this differs from an |
| <code>INPUT</code> command, because the linker will not search for the file in |
| the archive search path. |
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