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| <title>LD: Miscellaneous Commands</title> |
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| <a name="Miscellaneous-Commands"></a> |
| <div class="header"> |
| <p> |
| Previous: <a href="REGION_005fALIAS.html#REGION_005fALIAS" accesskey="p" rel="prev">REGION_ALIAS</a>, Up: <a href="Simple-Commands.html#Simple-Commands" accesskey="u" rel="up">Simple Commands</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="Other-Linker-Script-Commands"></a> |
| <h4 class="subsection">3.4.5 Other Linker Script Commands</h4> |
| <p>There are a few other linker scripts commands. |
| </p> |
| <dl compact="compact"> |
| <dt><code>ASSERT(<var>exp</var>, <var>message</var>)</code></dt> |
| <dd><a name="index-ASSERT"></a> |
| <a name="index-assertion-in-linker-script"></a> |
| <p>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>. |
| </p> |
| <p>Note that assertions are checked before the final stages of linking |
| take place. This means that expressions involving symbols PROVIDEd |
| inside section definitions will fail if the user has not set values |
| for those symbols. The only exception to this rule is PROVIDEd |
| symbols that just reference dot. Thus an assertion like this: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample"> .stack : |
| { |
| PROVIDE (__stack = .); |
| PROVIDE (__stack_size = 0x100); |
| ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack"); |
| } |
| </pre></div> |
| |
| <p>will fail if <code>__stack_size</code> is not defined elsewhere. Symbols |
| PROVIDEd outside of section definitions are evaluated earlier, so they |
| can be used inside ASSERTions. Thus: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample"> PROVIDE (__stack_size = 0x100); |
| .stack : |
| { |
| PROVIDE (__stack = .); |
| ASSERT ((__stack > (_end + __stack_size)), "Error: No room left for the stack"); |
| } |
| </pre></div> |
| |
| <p>will work. |
| </p> |
| </dd> |
| <dt><code>EXTERN(<var>symbol</var> <var>symbol</var> …)</code></dt> |
| <dd><a name="index-EXTERN"></a> |
| <a name="index-undefined-symbol-in-linker-script"></a> |
| <p>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>-u</samp>’ command-line option. |
| </p> |
| </dd> |
| <dt><code>FORCE_COMMON_ALLOCATION</code></dt> |
| <dd><a name="index-FORCE_005fCOMMON_005fALLOCATION"></a> |
| <a name="index-common-allocation-in-linker-script"></a> |
| <p>This command has the same effect as the ‘<samp>-d</samp>’ command-line option: |
| to make <code>ld</code> assign space to common symbols even if a relocatable |
| output file is specified (‘<samp>-r</samp>’). |
| </p> |
| </dd> |
| <dt><code>INHIBIT_COMMON_ALLOCATION</code></dt> |
| <dd><a name="index-INHIBIT_005fCOMMON_005fALLOCATION"></a> |
| <a name="index-common-allocation-in-linker-script-1"></a> |
| <p>This command has the same effect as the ‘<samp>--no-define-common</samp>’ |
| command-line option: to make <code>ld</code> omit the assignment of addresses |
| to common symbols even for a non-relocatable output file. |
| </p> |
| </dd> |
| <dt><code>INSERT [ AFTER | BEFORE ] <var>output_section</var></code></dt> |
| <dd><a name="index-INSERT"></a> |
| <a name="index-insert-user-script-into-default-script"></a> |
| <p>This command is typically used in a script specified by ‘<samp>-T</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>-T</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>-T</samp>’ scripts are parsed before the default |
| linker script, statements in the ‘<samp>-T</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>-T</samp>’ output sections before those in the default script. Here |
| is an example of how a ‘<samp>-T</samp>’ script using <code>INSERT</code> might look: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">SECTIONS |
| { |
| OVERLAY : |
| { |
| .ov1 { ov1*(.text) } |
| .ov2 { ov2*(.text) } |
| } |
| } |
| INSERT AFTER .text; |
| </pre></div> |
| |
| </dd> |
| <dt><code>NOCROSSREFS(<var>section</var> <var>section</var> …)</code></dt> |
| <dd><a name="index-NOCROSSREFS_0028sections_0029"></a> |
| <a name="index-cross-references"></a> |
| <p>This command may be used to tell <code>ld</code> to issue an error about any |
| references among certain output sections. |
| </p> |
| <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> |
| <p>The <code>NOCROSSREFS</code> command takes a list of output section names. If |
| <code>ld</code> 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. |
| </p> |
| </dd> |
| <dt><code>OUTPUT_ARCH(<var>bfdarch</var>)</code></dt> |
| <dd><a name="index-OUTPUT_005fARCH_0028bfdarch_0029"></a> |
| <a name="index-machine-architecture"></a> |
| <a name="index-architecture"></a> |
| <p>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>-f</samp>’ option. |
| </p> |
| </dd> |
| <dt><code>LD_FEATURE(<var>string</var>)</code></dt> |
| <dd><a name="index-LD_005fFEATURE_0028string_0029"></a> |
| <p>This command may be used to modify <code>ld</code> behavior. If |
| <var>string</var> is <code>"SANE_EXPR"</code> then absolute symbols and numbers |
| in a script are simply treated as numbers everywhere. |
| See <a href="Expression-Section.html#Expression-Section">Expression Section</a>. |
| </p></dd> |
| </dl> |
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