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<title>ABI (Debugging with GDB)</title>

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<a name="ABI"></a>
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<hr>
<a name="Configuring-the-Current-ABI"></a>
<h3 class="section">22.7 Configuring the Current ABI</h3>

<p><small>GDB</small> can determine the <em>ABI</em> (Application Binary Interface) of your
application automatically.  However, sometimes you need to override its
conclusions.  Use these commands to manage <small>GDB</small>&rsquo;s view of the
current ABI.
</p>
<a name="index-OS-ABI"></a>
<a name="index-set-osabi"></a>
<a name="index-show-osabi"></a>
<a name="index-Newlib-OS-ABI-and-its-influence-on-the-longjmp-handling"></a>

<p>One <small>GDB</small> configuration can debug binaries for multiple operating
system targets, either via remote debugging or native emulation.
<small>GDB</small> will autodetect the <em>OS ABI</em> (Operating System ABI) in use,
but you can override its conclusion using the <code>set osabi</code> command.
One example where this is useful is in debugging of binaries which use
an alternate C library (e.g. <small>UCLIBC</small> for <small>GNU</small>/Linux) which does
not have the same identifying marks that the standard C library for your
platform provides.
</p>
<p>When <small>GDB</small> is debugging the AArch64 architecture, it provides a
&ldquo;Newlib&rdquo; OS ABI.  This is useful for handling <code>setjmp</code> and
<code>longjmp</code> when debugging binaries that use the <small>NEWLIB</small> C library.
The &ldquo;Newlib&rdquo; OS ABI can be selected by <code>set osabi Newlib</code>.
</p>
<dl compact="compact">
<dt><code>show osabi</code></dt>
<dd><p>Show the OS ABI currently in use.
</p>
</dd>
<dt><code>set osabi</code></dt>
<dd><p>With no argument, show the list of registered available OS ABI&rsquo;s.
</p>
</dd>
<dt><code>set osabi <var>abi</var></code></dt>
<dd><p>Set the current OS ABI to <var>abi</var>.
</p></dd>
</dl>

<a name="index-float-promotion"></a>

<p>Generally, the way that an argument of type <code>float</code> is passed to a
function depends on whether the function is prototyped.  For a prototyped
(i.e. ANSI/ISO style) function, <code>float</code> arguments are passed unchanged,
according to the architecture&rsquo;s convention for <code>float</code>.  For unprototyped
(i.e. K&amp;R style) functions, <code>float</code> arguments are first promoted to type
<code>double</code> and then passed.
</p>
<p>Unfortunately, some forms of debug information do not reliably indicate whether
a function is prototyped.  If <small>GDB</small> calls a function that is not marked
as prototyped, it consults <kbd>set coerce-float-to-double</kbd>.
</p>
<dl compact="compact">
<dd><a name="index-set-coerce_002dfloat_002dto_002ddouble"></a>
</dd>
<dt><code>set coerce-float-to-double</code></dt>
<dt><code>set coerce-float-to-double on</code></dt>
<dd><p>Arguments of type <code>float</code> will be promoted to <code>double</code> when passed
to an unprototyped function.  This is the default setting.
</p>
</dd>
<dt><code>set coerce-float-to-double off</code></dt>
<dd><p>Arguments of type <code>float</code> will be passed directly to unprototyped
functions.
</p>
<a name="index-show-coerce_002dfloat_002dto_002ddouble"></a>
</dd>
<dt><code>show coerce-float-to-double</code></dt>
<dd><p>Show the current setting of promoting <code>float</code> to <code>double</code>.
</p></dd>
</dl>

<a name="index-set-cp_002dabi"></a>
<a name="index-show-cp_002dabi"></a>
<p><small>GDB</small> needs to know the ABI used for your program&rsquo;s C<tt>++</tt>
objects.  The correct C<tt>++</tt> ABI depends on which C<tt>++</tt> compiler was
used to build your application.  <small>GDB</small> only fully supports
programs with a single C<tt>++</tt> ABI; if your program contains code using
multiple C<tt>++</tt> ABI&rsquo;s or if <small>GDB</small> can not identify your
program&rsquo;s ABI correctly, you can tell <small>GDB</small> which ABI to use.
Currently supported ABI&rsquo;s include &ldquo;gnu-v2&rdquo;, for <code>g++</code> versions
before 3.0, &ldquo;gnu-v3&rdquo;, for <code>g++</code> versions 3.0 and later, and
&ldquo;hpaCC&rdquo; for the HP ANSI C<tt>++</tt> compiler.  Other C<tt>++</tt> compilers may
use the &ldquo;gnu-v2&rdquo; or &ldquo;gnu-v3&rdquo; ABI&rsquo;s as well.  The default setting is
&ldquo;auto&rdquo;.
</p>
<dl compact="compact">
<dt><code>show cp-abi</code></dt>
<dd><p>Show the C<tt>++</tt> ABI currently in use.
</p>
</dd>
<dt><code>set cp-abi</code></dt>
<dd><p>With no argument, show the list of supported C<tt>++</tt> ABI&rsquo;s.
</p>
</dd>
<dt><code>set cp-abi <var>abi</var></code></dt>
<dt><code>set cp-abi auto</code></dt>
<dd><p>Set the current C<tt>++</tt> ABI to <var>abi</var>, or return to automatic detection.
</p></dd>
</dl>

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