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<a name="Macros-Affecting-All-Debugging-Formats"></a>
<h4 class="subsection">18.21.1 Macros Affecting All Debugging Formats</h4>

<p>These macros affect all debugging formats.
</p>
<dl>
<dt><a name="index-DBX_005fREGISTER_005fNUMBER"></a>Macro: <strong>DBX_REGISTER_NUMBER</strong> <em>(<var>regno</var>)</em></dt>
<dd><p>A C expression that returns the DBX register number for the compiler
register number <var>regno</var>.  In the default macro provided, the value
of this expression will be <var>regno</var> itself.  But sometimes there are
some registers that the compiler knows about and DBX does not, or vice
versa.  In such cases, some register may need to have one number in the
compiler and another for DBX.
</p>
<p>If two registers have consecutive numbers inside GCC, and they can be
used as a pair to hold a multiword value, then they <em>must</em> have
consecutive numbers after renumbering with <code>DBX_REGISTER_NUMBER</code>.
Otherwise, debuggers will be unable to access such a pair, because they
expect register pairs to be consecutive in their own numbering scheme.
</p>
<p>If you find yourself defining <code>DBX_REGISTER_NUMBER</code> in way that
does not preserve register pairs, then what you must do instead is
redefine the actual register numbering scheme.
</p></dd></dl>

<dl>
<dt><a name="index-DEBUGGER_005fAUTO_005fOFFSET"></a>Macro: <strong>DEBUGGER_AUTO_OFFSET</strong> <em>(<var>x</var>)</em></dt>
<dd><p>A C expression that returns the integer offset value for an automatic
variable having address <var>x</var> (an RTL expression).  The default
computation assumes that <var>x</var> is based on the frame-pointer and
gives the offset from the frame-pointer.  This is required for targets
that produce debugging output for DBX and allow the frame-pointer to be
eliminated when the <samp>-g</samp> option is used.
</p></dd></dl>

<dl>
<dt><a name="index-DEBUGGER_005fARG_005fOFFSET"></a>Macro: <strong>DEBUGGER_ARG_OFFSET</strong> <em>(<var>offset</var>, <var>x</var>)</em></dt>
<dd><p>A C expression that returns the integer offset value for an argument
having address <var>x</var> (an RTL expression).  The nominal offset is
<var>offset</var>.
</p></dd></dl>

<dl>
<dt><a name="index-PREFERRED_005fDEBUGGING_005fTYPE"></a>Macro: <strong>PREFERRED_DEBUGGING_TYPE</strong></dt>
<dd><p>A C expression that returns the type of debugging output GCC should
produce when the user specifies just <samp>-g</samp>.  Define
this if you have arranged for GCC to support more than one format of
debugging output.  Currently, the allowable values are <code>DBX_DEBUG</code>,
<code>DWARF2_DEBUG</code>, <code>XCOFF_DEBUG</code>, <code>VMS_DEBUG</code>,
and <code>VMS_AND_DWARF2_DEBUG</code>.
</p>
<p>When the user specifies <samp>-ggdb</samp>, GCC normally also uses the
value of this macro to select the debugging output format, but with two
exceptions.  If <code>DWARF2_DEBUGGING_INFO</code> is defined, GCC uses the
value <code>DWARF2_DEBUG</code>.  Otherwise, if <code>DBX_DEBUGGING_INFO</code> is
defined, GCC uses <code>DBX_DEBUG</code>.
</p>
<p>The value of this macro only affects the default debugging output; the
user can always get a specific type of output by using <samp>-gstabs</samp>,
<samp>-gdwarf-2</samp>, <samp>-gxcoff</samp>, or <samp>-gvms</samp>.
</p></dd></dl>

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