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<title>Debugging with GDB: Inline Functions</title>

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<a name="Inline-Functions"></a>
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<a name="Inline-Functions-1"></a>
<h3 class="section">11.1 Inline Functions</h3>
<a name="index-inline-functions_002c-debugging"></a>

<p><em>Inlining</em> is an optimization that inserts a copy of the function
body directly at each call site, instead of jumping to a shared
routine.  <small>GDB</small> displays inlined functions just like
non-inlined functions.  They appear in backtraces.  You can view their
arguments and local variables, step into them with <code>step</code>, skip
them with <code>next</code>, and escape from them with <code>finish</code>.
You can check whether a function was inlined by using the
<code>info frame</code> command.
</p>
<p>For <small>GDB</small> to support inlined functions, the compiler must
record information about inlining in the debug information &mdash;
<small>GCC</small> using the <small>DWARF 2</small> format does this, and several
other compilers do also.  <small>GDB</small> only supports inlined functions
when using <small>DWARF 2</small>.  Versions of <small>GCC</small> before 4.1
do not emit two required attributes (&lsquo;<samp>DW_AT_call_file</samp>&rsquo; and
&lsquo;<samp>DW_AT_call_line</samp>&rsquo;); <small>GDB</small> does not display inlined
function calls with earlier versions of <small>GCC</small>.  It instead
displays the arguments and local variables of inlined functions as
local variables in the caller.
</p>
<p>The body of an inlined function is directly included at its call site;
unlike a non-inlined function, there are no instructions devoted to
the call.  <small>GDB</small> still pretends that the call site and the
start of the inlined function are different instructions.  Stepping to
the call site shows the call site, and then stepping again shows
the first line of the inlined function, even though no additional
instructions are executed.
</p>
<p>This makes source-level debugging much clearer; you can see both the
context of the call and then the effect of the call.  Only stepping by
a single instruction using <code>stepi</code> or <code>nexti</code> does not do
this; single instruction steps always show the inlined body.
</p>
<p>There are some ways that <small>GDB</small> does not pretend that inlined
function calls are the same as normal calls:
</p>
<ul>
<li> Setting breakpoints at the call site of an inlined function may not
work, because the call site does not contain any code.  <small>GDB</small>
may incorrectly move the breakpoint to the next line of the enclosing
function, after the call.  This limitation will be removed in a future
version of <small>GDB</small>; until then, set a breakpoint on an earlier line
or inside the inlined function instead.

</li><li> <small>GDB</small> cannot locate the return value of inlined calls after
using the <code>finish</code> command.  This is a limitation of compiler-generated
debugging information; after <code>finish</code>, you can step to the next line
and print a variable where your program stored the return value.

</li></ul>

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