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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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<div class="header">
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<p>
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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> [<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>
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<a name="Pointer-Bounds-Checker-Built_002din-Functions"></a>
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<h3 class="section">6.56 Pointer Bounds Checker Built-in Functions</h3>
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<a name="index-Pointer-Bounds-Checker-builtins"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fset_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fnarrow_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fcopy_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005finit_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fnull_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fstore_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005flbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fubounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fbounds"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005flbound"></a>
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<a name="index-_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005fubound"></a>
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<p>GCC provides a set of built-in functions to control Pointer Bounds Checker
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instrumentation. Note that all Pointer Bounds Checker builtins can be used
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even if you compile with Pointer Bounds Checker off
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(<samp>-fno-check-pointer-bounds</samp>).
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The behavior may differ in such case as documented below.
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</p>
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<dl>
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<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>
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<dd>
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<p>This built-in function returns a new pointer with the value of <var>q</var>, and
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associate it with the bounds [<var>q</var>, <var>q</var>+<var>size</var>-1]. With Pointer
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Bounds Checker off, the built-in function just returns the first argument.
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</p>
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<div class="smallexample">
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<pre class="smallexample">extern void *__wrap_malloc (size_t n)
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{
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void *p = (void *)__real_malloc (n);
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if (!p) return __builtin___bnd_null_ptr_bounds (p);
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return __builtin___bnd_set_ptr_bounds (p, n);
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}
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</pre></div>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function returns a new pointer with the value of <var>p</var>
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and associates it with the narrowed bounds formed by the intersection
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of bounds associated with <var>q</var> and the bounds
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[<var>p</var>, <var>p</var> + <var>size</var> - 1].
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With Pointer Bounds Checker off, the built-in function just returns the first
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argument.
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</p>
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<div class="smallexample">
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<pre class="smallexample">void init_objects (object *objs, size_t size)
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{
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size_t i;
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/* Initialize objects one-by-one passing pointers with bounds of
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an object, not the full array of objects. */
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for (i = 0; i < size; i++)
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init_object (__builtin___bnd_narrow_ptr_bounds (objs + i, objs,
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sizeof(object)));
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}
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</pre></div>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function returns a new pointer with the value of <var>q</var>,
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and associates it with the bounds already associated with pointer <var>r</var>.
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With Pointer Bounds Checker off, the built-in function just returns the first
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argument.
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</p>
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<div class="smallexample">
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<pre class="smallexample">/* Here is a way to get pointer to object's field but
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still with the full object's bounds. */
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int *field_ptr = __builtin___bnd_copy_ptr_bounds (&objptr->int_field,
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objptr);
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</pre></div>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function returns a new pointer with the value of <var>q</var>, and
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associates it with INIT (allowing full memory access) bounds. With Pointer
|
Bounds Checker off, the built-in function just returns the first argument.
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</p>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function returns a new pointer with the value of <var>q</var>, and
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associates it with NULL (allowing no memory access) bounds. With Pointer
|
Bounds Checker off, the built-in function just returns the first argument.
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</p>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function stores the bounds associated with pointer <var>ptr_val</var>
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and location <var>ptr_addr</var> into Bounds Table. This can be useful to propagate
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bounds from legacy code without touching the associated pointer’s memory when
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pointers are copied as integers. With Pointer Bounds Checker off, the built-in
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function call is ignored.
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</p>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function checks if the pointer <var>q</var> is within the lower
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bound of its associated bounds. With Pointer Bounds Checker off, the built-in
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function call is ignored.
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</p>
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<div class="smallexample">
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<pre class="smallexample">extern void *__wrap_memset (void *dst, int c, size_t len)
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{
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if (len > 0)
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{
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__builtin___bnd_chk_ptr_lbounds (dst);
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__builtin___bnd_chk_ptr_ubounds ((char *)dst + len - 1);
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__real_memset (dst, c, len);
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}
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return dst;
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}
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</pre></div>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function checks if the pointer <var>q</var> is within the upper
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bound of its associated bounds. With Pointer Bounds Checker off, the built-in
|
function call is ignored.
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</p>
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</dd></dl>
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<dl>
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<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>
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<dd>
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<p>This built-in function checks if [<var>q</var>, <var>q</var> + <var>size</var> - 1] is within
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the lower and upper bounds associated with <var>q</var>. With Pointer Bounds Checker
|
off, the built-in function call is ignored.
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</p>
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<div class="smallexample">
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<pre class="smallexample">extern void *__wrap_memcpy (void *dst, const void *src, size_t n)
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{
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if (n > 0)
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{
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__bnd_chk_ptr_bounds (dst, n);
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__bnd_chk_ptr_bounds (src, n);
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__real_memcpy (dst, src, n);
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}
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return dst;
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}
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</pre></div>
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</dd></dl>
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<dl>
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<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>
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<p>This built-in function returns the lower bound associated
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with the pointer <var>q</var>, as a pointer value.
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This is useful for debugging using <code>printf</code>.
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With Pointer Bounds Checker off, the built-in function returns 0.
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</p>
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<div class="smallexample">
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<pre class="smallexample">void *lb = __builtin___bnd_get_ptr_lbound (q);
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void *ub = __builtin___bnd_get_ptr_ubound (q);
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printf ("q = %p lb(q) = %p ub(q) = %p", q, lb, ub);
|
</pre></div>
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</dd></dl>
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<dl>
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<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,
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the built-in function returns -1.
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</p>
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</dd></dl>
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<hr>
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<div class="header">
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<p>
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