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<h4 class="subsection">21.4.4 MIPS</h4>

<p><a name="index-stack-on-Alpha-1401"></a><a name="index-stack-on-MIPS-1402"></a><a name="index-Alpha-stack-1403"></a><a name="index-MIPS-stack-1404"></a>Alpha- and MIPS-based computers use an unusual stack frame, which
sometimes requires <span class="sc">gdb</span> to search backward in the object code to
find the beginning of a function.

   <p><a name="index-response-time_002c-MIPS-debugging-1405"></a>To improve response time (especially for embedded applications, where
<span class="sc">gdb</span> may be restricted to a slow serial line for this search)
you may want to limit the size of this search, using one of these
commands:

     
<a name="index-g_t_0040code_007bheuristic_002dfence_002dpost_007d-_0028Alpha_002c-MIPS_0029-1406"></a>
<dl><dt><code>set heuristic-fence-post </code><var>limit</var><dd>Restrict <span class="sc">gdb</span> to examining at most <var>limit</var> bytes in its
search for the beginning of a function.  A value of <var>0</var> (the
default) means there is no limit.  However, except for <var>0</var>, the
larger the limit the more bytes <code>heuristic-fence-post</code> must search
and therefore the longer it takes to run.  You should only need to use
this command when debugging a stripped executable.

     <br><dt><code>show heuristic-fence-post</code><dd>Display the current limit. 
</dl>

<p class="noindent">These commands are available <em>only</em> when <span class="sc">gdb</span> is configured
for debugging programs on Alpha or MIPS processors.

   <p>Several MIPS-specific commands are available when debugging MIPS
programs:

     <dl>
<dt><code>set mips abi </code><var>arg</var><dd><a name="index-set-mips-abi-1407"></a><a name="index-set-ABI-for-MIPS-1408"></a>Tell <span class="sc">gdb</span> which MIPS ABI is used by the inferior.  Possible
values of <var>arg</var> are:

          <dl>
<dt>&lsquo;<samp><span class="samp">auto</span></samp>&rsquo;<dd>The default ABI associated with the current binary (this is the
default). 
<br><dt>&lsquo;<samp><span class="samp">o32</span></samp>&rsquo;<br><dt>&lsquo;<samp><span class="samp">o64</span></samp>&rsquo;<br><dt>&lsquo;<samp><span class="samp">n32</span></samp>&rsquo;<br><dt>&lsquo;<samp><span class="samp">n64</span></samp>&rsquo;<br><dt>&lsquo;<samp><span class="samp">eabi32</span></samp>&rsquo;<br><dt>&lsquo;<samp><span class="samp">eabi64</span></samp>&rsquo;<dd></dl>

     <br><dt><code>show mips abi</code><dd><a name="index-show-mips-abi-1409"></a>Show the MIPS ABI used by <span class="sc">gdb</span> to debug the inferior.

     <br><dt><code>set mips compression </code><var>arg</var><dd><a name="index-set-mips-compression-1410"></a><a name="index-MIPS-code-compression-1411"></a>Tell <span class="sc">gdb</span> which MIPS compressed ISA encoding is used by the
inferior.  <span class="sc">gdb</span> uses this for code disassembly and other
internal interpretation purposes.  This setting is only referred to
when no executable has been associated with the debugging session or
the executable does not provide information about the encoding it uses. 
Otherwise this setting is automatically updated from information
provided by the executable.

     <p>Possible values of <var>arg</var> are &lsquo;<samp><span class="samp">mips16</span></samp>&rsquo; and &lsquo;<samp><span class="samp">micromips</span></samp>&rsquo;. 
The default compressed ISA encoding is &lsquo;<samp><span class="samp">mips16</span></samp>&rsquo;, as executables
containing MIPS16 code frequently are not identified as such.

     <p>This setting is &ldquo;sticky&rdquo;; that is, it retains its value across
debugging sessions until reset either explicitly with this command or
implicitly from an executable.

     <p>The compiler and/or assembler typically add symbol table annotations to
identify functions compiled for the MIPS16 or microMIPS ISAs.  If these
function-scope annotations are present, <span class="sc">gdb</span> uses them in
preference to the global compressed ISA encoding setting.

     <br><dt><code>show mips compression</code><dd><a name="index-show-mips-compression-1412"></a>Show the MIPS compressed ISA encoding used by <span class="sc">gdb</span> to debug the
inferior.

     <br><dt><code>set mipsfpu</code><dt><code>show mipsfpu</code><dd>See <a href="MIPS-Embedded.html#MIPS-Embedded">set mipsfpu</a>.

     <br><dt><code>set mips mask-address </code><var>arg</var><dd><a name="index-set-mips-mask_002daddress-1413"></a><a name="index-MIPS-addresses_002c-masking-1414"></a>This command determines whether the most-significant 32 bits of 64-bit
MIPS addresses are masked off.  The argument <var>arg</var> can be
&lsquo;<samp><span class="samp">on</span></samp>&rsquo;, &lsquo;<samp><span class="samp">off</span></samp>&rsquo;, or &lsquo;<samp><span class="samp">auto</span></samp>&rsquo;.  The latter is the default
setting, which lets <span class="sc">gdb</span> determine the correct value.

     <br><dt><code>show mips mask-address</code><dd><a name="index-show-mips-mask_002daddress-1415"></a>Show whether the upper 32 bits of MIPS addresses are masked off or
not.

     <br><dt><code>set remote-mips64-transfers-32bit-regs</code><dd><a name="index-set-remote_002dmips64_002dtransfers_002d32bit_002dregs-1416"></a>This command controls compatibility with 64-bit MIPS targets that
transfer data in 32-bit quantities.  If you have an old MIPS 64 target
that transfers 32 bits for some registers, like <span class="sc">sr</span> and <span class="sc">fsr</span>,
and 64 bits for other registers, set this option to &lsquo;<samp><span class="samp">on</span></samp>&rsquo;.

     <br><dt><code>show remote-mips64-transfers-32bit-regs</code><dd><a name="index-show-remote_002dmips64_002dtransfers_002d32bit_002dregs-1417"></a>Show the current setting of compatibility with older MIPS 64 targets.

     <br><dt><code>set debug mips</code><dd><a name="index-set-debug-mips-1418"></a>This command turns on and off debugging messages for the MIPS-specific
target code in <span class="sc">gdb</span>.

     <br><dt><code>show debug mips</code><dd><a name="index-show-debug-mips-1419"></a>Show the current setting of MIPS debugging messages. 
</dl>

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