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<title>Debugging with GDB: ABI</title>
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<a name="ABI"></a>
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<div class="header">
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<p>
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Next: <a href="Auto_002dloading.html#Auto_002dloading" accesskey="n" rel="next">Auto-loading</a>, Previous: <a href="Numbers.html#Numbers" accesskey="p" rel="previous">Numbers</a>, Up: <a href="Controlling-GDB.html#Controlling-GDB" accesskey="u" rel="up">Controlling GDB</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="Configuring-the-Current-ABI"></a>
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<h3 class="section">22.7 Configuring the Current ABI</h3>
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<p><small>GDB</small> can determine the <em>ABI</em> (Application Binary Interface) of your
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application automatically. However, sometimes you need to override its
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conclusions. Use these commands to manage <small>GDB</small>’s view of the
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current ABI.
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</p>
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<a name="index-OS-ABI"></a>
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<a name="index-set-osabi"></a>
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<a name="index-show-osabi"></a>
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<a name="index-Newlib-OS-ABI-and-its-influence-on-the-longjmp-handling"></a>
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<p>One <small>GDB</small> configuration can debug binaries for multiple operating
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system targets, either via remote debugging or native emulation.
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<small>GDB</small> will autodetect the <em>OS ABI</em> (Operating System ABI) in use,
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but you can override its conclusion using the <code>set osabi</code> command.
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One example where this is useful is in debugging of binaries which use
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an alternate C library (e.g. <small>UCLIBC</small> for <small>GNU</small>/Linux) which does
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not have the same identifying marks that the standard C library for your
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platform provides.
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</p>
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<p>When <small>GDB</small> is debugging the AArch64 architecture, it provides a
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“Newlib” OS ABI. This is useful for handling <code>setjmp</code> and
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<code>longjmp</code> when debugging binaries that use the <small>NEWLIB</small> C library.
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The “Newlib” OS ABI can be selected by <code>set osabi Newlib</code>.
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</p>
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<dl compact="compact">
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<dt><code>show osabi</code></dt>
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<dd><p>Show the OS ABI currently in use.
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</p>
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</dd>
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<dt><code>set osabi</code></dt>
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<dd><p>With no argument, show the list of registered available OS ABI’s.
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</p>
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</dd>
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<dt><code>set osabi <var>abi</var></code></dt>
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<dd><p>Set the current OS ABI to <var>abi</var>.
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</p></dd>
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</dl>
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<a name="index-float-promotion"></a>
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<p>Generally, the way that an argument of type <code>float</code> is passed to a
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function depends on whether the function is prototyped. For a prototyped
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(i.e. ANSI/ISO style) function, <code>float</code> arguments are passed unchanged,
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according to the architecture’s convention for <code>float</code>. For unprototyped
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(i.e. K&R style) functions, <code>float</code> arguments are first promoted to type
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<code>double</code> and then passed.
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</p>
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<p>Unfortunately, some forms of debug information do not reliably indicate whether
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a function is prototyped. If <small>GDB</small> calls a function that is not marked
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as prototyped, it consults <kbd>set coerce-float-to-double</kbd>.
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</p>
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<dl compact="compact">
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<dd><a name="index-set-coerce_002dfloat_002dto_002ddouble"></a>
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</dd>
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<dt><code>set coerce-float-to-double</code></dt>
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<dt><code>set coerce-float-to-double on</code></dt>
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<dd><p>Arguments of type <code>float</code> will be promoted to <code>double</code> when passed
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to an unprototyped function. This is the default setting.
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</p>
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</dd>
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<dt><code>set coerce-float-to-double off</code></dt>
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<dd><p>Arguments of type <code>float</code> will be passed directly to unprototyped
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functions.
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</p>
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<a name="index-show-coerce_002dfloat_002dto_002ddouble"></a>
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</dd>
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<dt><code>show coerce-float-to-double</code></dt>
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<dd><p>Show the current setting of promoting <code>float</code> to <code>double</code>.
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</p></dd>
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</dl>
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<a name="index-set-cp_002dabi"></a>
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<a name="index-show-cp_002dabi"></a>
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<p><small>GDB</small> needs to know the ABI used for your program’s C<tt>++</tt>
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objects. The correct C<tt>++</tt> ABI depends on which C<tt>++</tt> compiler was
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used to build your application. <small>GDB</small> only fully supports
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programs with a single C<tt>++</tt> ABI; if your program contains code using
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multiple C<tt>++</tt> ABI’s or if <small>GDB</small> can not identify your
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program’s ABI correctly, you can tell <small>GDB</small> which ABI to use.
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Currently supported ABI’s include “gnu-v2”, for <code>g++</code> versions
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before 3.0, “gnu-v3”, for <code>g++</code> versions 3.0 and later, and
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“hpaCC” for the HP ANSI C<tt>++</tt> compiler. Other C<tt>++</tt> compilers may
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use the “gnu-v2” or “gnu-v3” ABI’s as well. The default setting is
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“auto”.
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</p>
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<dl compact="compact">
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<dt><code>show cp-abi</code></dt>
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<dd><p>Show the C<tt>++</tt> ABI currently in use.
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</p>
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</dd>
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<dt><code>set cp-abi</code></dt>
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<dd><p>With no argument, show the list of supported C<tt>++</tt> ABI’s.
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</p>
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</dd>
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<dt><code>set cp-abi <var>abi</var></code></dt>
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<dt><code>set cp-abi auto</code></dt>
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<dd><p>Set the current C<tt>++</tt> ABI to <var>abi</var>, or return to automatic detection.
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</p></dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Auto_002dloading.html#Auto_002dloading" accesskey="n" rel="next">Auto-loading</a>, Previous: <a href="Numbers.html#Numbers" accesskey="p" rel="previous">Numbers</a>, Up: <a href="Controlling-GDB.html#Controlling-GDB" accesskey="u" rel="up">Controlling GDB</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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