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| <h4 class="subsection">3.4.5 Other Linker Script Commands</h4> |
| |
| <p>There are a few other linker scripts commands. |
| |
| <dl> |
| <dt><code>ASSERT(</code><var>exp</var><code>, </code><var>message</var><code>)</code><dd><a name="index-ASSERT-371"></a><a name="index-assertion-in-linker-script-372"></a>Ensure that <var>exp</var> is non-zero. If it is zero, then exit the linker |
| with an error code, and print <var>message</var>. |
| |
| <br><dt><code>EXTERN(</code><var>symbol</var> <var>symbol</var><code> ...)</code><dd><a name="index-EXTERN-373"></a><a name="index-undefined-symbol-in-linker-script-374"></a>Force <var>symbol</var> to be entered in the output file as an undefined |
| symbol. Doing this may, for example, trigger linking of additional |
| modules from standard libraries. You may list several <var>symbol</var>s for |
| each <code>EXTERN</code>, and you may use <code>EXTERN</code> multiple times. This |
| command has the same effect as the ‘<samp><span class="samp">-u</span></samp>’ command-line option. |
| |
| <br><dt><code>FORCE_COMMON_ALLOCATION</code><dd><a name="index-FORCE_005fCOMMON_005fALLOCATION-375"></a><a name="index-common-allocation-in-linker-script-376"></a>This command has the same effect as the ‘<samp><span class="samp">-d</span></samp>’ command-line option: |
| to make <samp><span class="command">ld</span></samp> assign space to common symbols even if a relocatable |
| output file is specified (‘<samp><span class="samp">-r</span></samp>’). |
| |
| <br><dt><code>INHIBIT_COMMON_ALLOCATION</code><dd><a name="index-INHIBIT_005fCOMMON_005fALLOCATION-377"></a><a name="index-common-allocation-in-linker-script-378"></a>This command has the same effect as the ‘<samp><span class="samp">--no-define-common</span></samp>’ |
| command-line option: to make <code>ld</code> omit the assignment of addresses |
| to common symbols even for a non-relocatable output file. |
| |
| <br><dt><code>INSERT [ AFTER | BEFORE ] </code><var>output_section</var><dd><a name="index-INSERT-379"></a><a name="index-insert-user-script-into-default-script-380"></a>This command is typically used in a script specified by ‘<samp><span class="samp">-T</span></samp>’ to |
| augment the default <code>SECTIONS</code> with, for example, overlays. It |
| inserts all prior linker script statements after (or before) |
| <var>output_section</var>, and also causes ‘<samp><span class="samp">-T</span></samp>’ to not override the |
| default linker script. The exact insertion point is as for orphan |
| sections. See <a href="Location-Counter.html#Location-Counter">Location Counter</a>. The insertion happens after the |
| linker has mapped input sections to output sections. Prior to the |
| insertion, since ‘<samp><span class="samp">-T</span></samp>’ scripts are parsed before the default |
| linker script, statements in the ‘<samp><span class="samp">-T</span></samp>’ script occur before the |
| default linker script statements in the internal linker representation |
| of the script. In particular, input section assignments will be made |
| to ‘<samp><span class="samp">-T</span></samp>’ output sections before those in the default script. Here |
| is an example of how a ‘<samp><span class="samp">-T</span></samp>’ script using <code>INSERT</code> might look: |
| |
| <pre class="smallexample"> SECTIONS |
| { |
| OVERLAY : |
| { |
| .ov1 { ov1*(.text) } |
| .ov2 { ov2*(.text) } |
| } |
| } |
| INSERT AFTER .text; |
| </pre> |
| <br><dt><code>NOCROSSREFS(</code><var>section</var> <var>section</var><code> ...)</code><dd><a name="index-NOCROSSREFS_0028_0040var_007bsections_007d_0029-381"></a><a name="index-cross-references-382"></a>This command may be used to tell <samp><span class="command">ld</span></samp> to issue an error about any |
| references among certain output sections. |
| |
| <p>In certain types of programs, particularly on embedded systems when |
| using overlays, when one section is loaded into memory, another section |
| will not be. Any direct references between the two sections would be |
| errors. For example, it would be an error if code in one section called |
| a function defined in the other section. |
| |
| <p>The <code>NOCROSSREFS</code> command takes a list of output section names. If |
| <samp><span class="command">ld</span></samp> detects any cross references between the sections, it reports |
| an error and returns a non-zero exit status. Note that the |
| <code>NOCROSSREFS</code> command uses output section names, not input section |
| names. |
| |
| <br><dt><code>OUTPUT_ARCH(</code><var>bfdarch</var><code>)</code><dd><a name="index-OUTPUT_005fARCH_0028_0040var_007bbfdarch_007d_0029-383"></a><a name="index-machine-architecture-384"></a><a name="index-architecture-385"></a>Specify a particular output machine architecture. The argument is one |
| of the names used by the BFD library (see <a href="BFD.html#BFD">BFD</a>). You can see the |
| architecture of an object file by using the <code>objdump</code> program with |
| the ‘<samp><span class="samp">-f</span></samp>’ option. |
| </dl> |
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