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<title>Using the GNU Compiler Collection (GCC): Pointer Bounds Checker builtins</title>

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<a name="Pointer-Bounds-Checker-builtins"></a>
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<p>
Next: <a href="Cilk-Plus-Builtins.html#Cilk-Plus-Builtins" accesskey="n" rel="next">Cilk Plus Builtins</a>, Previous: <a href="Object-Size-Checking.html#Object-Size-Checking" accesskey="p" rel="prev">Object Size Checking</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Pointer-Bounds-Checker-Built_002din-Functions"></a>
<h3 class="section">6.57 Pointer Bounds Checker Built-in Functions</h3>
<a name="index-Pointer-Bounds-Checker-builtins"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fset_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fnarrow_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fcopy_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005finit_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fnull_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fstore_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005flbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fubounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fbounds"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005flbound"></a>
<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005fubound"></a>

<p>GCC provides a set of built-in functions to control Pointer Bounds Checker
instrumentation.  Note that all Pointer Bounds Checker builtins can be used
even if you compile with Pointer Bounds Checker off
(<samp>-fno-check-pointer-bounds</samp>).
The behavior may differ in such case as documented below.
</p>
<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fset_005fptr_005fbounds-1"></a>Built-in Function: <em>void *</em> <strong>__builtin___bnd_set_ptr_bounds</strong> <em>(const void *<var>q</var>, size_t <var>size</var>)</em></dt>
<dd>
<p>This built-in function returns a new pointer with the value of <var>q</var>, and
associate it with the bounds [<var>q</var>, <var>q</var>+<var>size</var>-1].  With Pointer
Bounds Checker off, the built-in function just returns the first argument.
</p>
<div class="smallexample">
<pre class="smallexample">extern void *__wrap_malloc (size_t n)
{
  void *p = (void *)__real_malloc (n);
  if (!p) return __builtin___bnd_null_ptr_bounds (p);
  return __builtin___bnd_set_ptr_bounds (p, n);
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fnarrow_005fptr_005fbounds-1"></a>Built-in Function: <em>void *</em> <strong>__builtin___bnd_narrow_ptr_bounds</strong> <em>(const void *<var>p</var>, const void *<var>q</var>, size_t  <var>size</var>)</em></dt>
<dd>
<p>This built-in function returns a new pointer with the value of <var>p</var>
and associates it with the narrowed bounds formed by the intersection
of bounds associated with <var>q</var> and the bounds
[<var>p</var>, <var>p</var> + <var>size</var> - 1].
With Pointer Bounds Checker off, the built-in function just returns the first
argument.
</p>
<div class="smallexample">
<pre class="smallexample">void init_objects (object *objs, size_t size)
{
  size_t i;
  /* Initialize objects one-by-one passing pointers with bounds of 
     an object, not the full array of objects.  */
  for (i = 0; i &lt; size; i++)
    init_object (__builtin___bnd_narrow_ptr_bounds (objs + i, objs,
                                                    sizeof(object)));
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fcopy_005fptr_005fbounds-1"></a>Built-in Function: <em>void *</em> <strong>__builtin___bnd_copy_ptr_bounds</strong> <em>(const void *<var>q</var>, const void *<var>r</var>)</em></dt>
<dd>
<p>This built-in function returns a new pointer with the value of <var>q</var>,
and associates it with the bounds already associated with pointer <var>r</var>.
With Pointer Bounds Checker off, the built-in function just returns the first
argument.
</p>
<div class="smallexample">
<pre class="smallexample">/* Here is a way to get pointer to object's field but
   still with the full object's bounds.  */
int *field_ptr = __builtin___bnd_copy_ptr_bounds (&amp;objptr-&gt;int_field, 
                                                  objptr);
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005finit_005fptr_005fbounds-1"></a>Built-in Function: <em>void *</em> <strong>__builtin___bnd_init_ptr_bounds</strong> <em>(const void *<var>q</var>)</em></dt>
<dd>
<p>This built-in function returns a new pointer with the value of <var>q</var>, and
associates it with INIT (allowing full memory access) bounds. With Pointer
Bounds Checker off, the built-in function just returns the first argument.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fnull_005fptr_005fbounds-1"></a>Built-in Function: <em>void *</em> <strong>__builtin___bnd_null_ptr_bounds</strong> <em>(const void *<var>q</var>)</em></dt>
<dd>
<p>This built-in function returns a new pointer with the value of <var>q</var>, and
associates it with NULL (allowing no memory access) bounds. With Pointer
Bounds Checker off, the built-in function just returns the first argument.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fstore_005fptr_005fbounds-1"></a>Built-in Function: <em>void</em> <strong>__builtin___bnd_store_ptr_bounds</strong> <em>(const void **<var>ptr_addr</var>, const void *<var>ptr_val</var>)</em></dt>
<dd>
<p>This built-in function stores the bounds associated with pointer <var>ptr_val</var>
and location <var>ptr_addr</var> into Bounds Table.  This can be useful to propagate
bounds from legacy code without touching the associated pointer&rsquo;s memory when
pointers are copied as integers.  With Pointer Bounds Checker off, the built-in
function call is ignored.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005flbounds-1"></a>Built-in Function: <em>void</em> <strong>__builtin___bnd_chk_ptr_lbounds</strong> <em>(const void *<var>q</var>)</em></dt>
<dd>
<p>This built-in function checks if the pointer <var>q</var> is within the lower
bound of its associated bounds.  With Pointer Bounds Checker off, the built-in
function call is ignored.
</p>
<div class="smallexample">
<pre class="smallexample">extern void *__wrap_memset (void *dst, int c, size_t len)
{
  if (len &gt; 0)
    {
      __builtin___bnd_chk_ptr_lbounds (dst);
      __builtin___bnd_chk_ptr_ubounds ((char *)dst + len - 1);
      __real_memset (dst, c, len);
    }
  return dst;
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fubounds-1"></a>Built-in Function: <em>void</em> <strong>__builtin___bnd_chk_ptr_ubounds</strong> <em>(const void *<var>q</var>)</em></dt>
<dd>
<p>This built-in function checks if the pointer <var>q</var> is within the upper
bound of its associated bounds.  With Pointer Bounds Checker off, the built-in
function call is ignored.
</p>
</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fbounds-1"></a>Built-in Function: <em>void</em> <strong>__builtin___bnd_chk_ptr_bounds</strong> <em>(const void *<var>q</var>, size_t <var>size</var>)</em></dt>
<dd>
<p>This built-in function checks if [<var>q</var>, <var>q</var> + <var>size</var> - 1] is within
the lower and upper bounds associated with <var>q</var>.  With Pointer Bounds Checker
off, the built-in function call is ignored.
</p>
<div class="smallexample">
<pre class="smallexample">extern void *__wrap_memcpy (void *dst, const void *src, size_t n)
{
  if (n &gt; 0)
    {
      __bnd_chk_ptr_bounds (dst, n);
      __bnd_chk_ptr_bounds (src, n);
      __real_memcpy (dst, src, n);
    }
  return dst;
}
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005flbound-1"></a>Built-in Function: <em>const void *</em> <strong>__builtin___bnd_get_ptr_lbound</strong> <em>(const void *<var>q</var>)</em></dt>
<dd>
<p>This built-in function returns the lower bound associated
with the pointer <var>q</var>, as a pointer value.  
This is useful for debugging using <code>printf</code>.
With Pointer Bounds Checker off, the built-in function returns 0.
</p>
<div class="smallexample">
<pre class="smallexample">void *lb = __builtin___bnd_get_ptr_lbound (q);
void *ub = __builtin___bnd_get_ptr_ubound (q);
printf (&quot;q = %p  lb(q) = %p  ub(q) = %p&quot;, q, lb, ub);
</pre></div>

</dd></dl>

<dl>
<dt><a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005fubound-1"></a>Built-in Function: <em>const void *</em> <strong>__builtin___bnd_get_ptr_ubound</strong> <em>(const void *<var>q</var>)</em></dt>
<dd>
<p>This built-in function returns the upper bound (which is a pointer) associated
with the pointer <var>q</var>.  With Pointer Bounds Checker off,
the built-in function returns -1.
</p>
</dd></dl>

<hr>
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