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220 lines
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220 lines
12 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Pointer Bounds Checker builtins - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="C-Extensions.html#C-Extensions" title="C Extensions">
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<link rel="prev" href="Object-Size-Checking.html#Object-Size-Checking" title="Object Size Checking">
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<link rel="next" href="Cilk-Plus-Builtins.html#Cilk-Plus-Builtins" title="Cilk Plus Builtins">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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</head>
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<body>
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<div class="node">
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<a name="Pointer-Bounds-Checker-builtins"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Cilk-Plus-Builtins.html#Cilk-Plus-Builtins">Cilk Plus Builtins</a>,
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Previous: <a rel="previous" accesskey="p" href="Object-Size-Checking.html#Object-Size-Checking">Object Size Checking</a>,
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Up: <a rel="up" accesskey="u" href="C-Extensions.html#C-Extensions">C Extensions</a>
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<hr>
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</div>
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<h3 class="section">6.55 Pointer Bounds Checker Built-in Functions</h3>
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<p><a name="index-Pointer-Bounds-Checker-builtins-3602"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fset_005fptr_005fbounds-3603"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fnarrow_005fptr_005fbounds-3604"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fcopy_005fptr_005fbounds-3605"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005finit_005fptr_005fbounds-3606"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fnull_005fptr_005fbounds-3607"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fstore_005fptr_005fbounds-3608"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005flbounds-3609"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fubounds-3610"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fbounds-3611"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005flbound-3612"></a><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005fubound-3613"></a>
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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><span class="option">-fno-check-pointer-bounds</span></samp>).
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The behavior may differ in such case as documented below.
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<div class="defun">
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— Built-in Function: void * <b>__builtin___bnd_set_ptr_bounds</b> (<var>const void *q, size_t size</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fset_005fptr_005fbounds-3614"></a></var><br>
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<blockquote>
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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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<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>
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void * <b>__builtin___bnd_narrow_ptr_bounds</b> (<var>const void *p, const void *q, size_t size</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fnarrow_005fptr_005fbounds-3615"></a></var><br>
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<blockquote>
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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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<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>
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void * <b>__builtin___bnd_copy_ptr_bounds</b> (<var>const void *q, const void *r</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fcopy_005fptr_005fbounds-3616"></a></var><br>
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<blockquote>
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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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<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>
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void * <b>__builtin___bnd_init_ptr_bounds</b> (<var>const void *q</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005finit_005fptr_005fbounds-3617"></a></var><br>
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<blockquote>
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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
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Bounds Checker off, the built-in function just returns the first argument.
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void * <b>__builtin___bnd_null_ptr_bounds</b> (<var>const void *q</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fnull_005fptr_005fbounds-3618"></a></var><br>
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<blockquote>
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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
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Bounds Checker off, the built-in function just returns the first argument.
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void <b>__builtin___bnd_store_ptr_bounds</b> (<var>const void **ptr_addr, const void *ptr_val</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fstore_005fptr_005fbounds-3619"></a></var><br>
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<blockquote>
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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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</blockquote></div>
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<div class="defun">
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— Built-in Function: void <b>__builtin___bnd_chk_ptr_lbounds</b> (<var>const void *q</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005flbounds-3620"></a></var><br>
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<blockquote>
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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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<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>
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void <b>__builtin___bnd_chk_ptr_ubounds</b> (<var>const void *q</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fubounds-3621"></a></var><br>
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<blockquote>
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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
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function call is ignored.
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</blockquote></div>
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<div class="defun">
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— Built-in Function: void <b>__builtin___bnd_chk_ptr_bounds</b> (<var>const void *q, size_t size</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fchk_005fptr_005fbounds-3622"></a></var><br>
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<blockquote>
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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
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off, the built-in function call is ignored.
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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>
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</blockquote></div>
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<div class="defun">
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— Built-in Function: const void * <b>__builtin___bnd_get_ptr_lbound</b> (<var>const void *q</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005flbound-3623"></a></var><br>
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<blockquote>
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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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<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);
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</pre>
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</blockquote></div>
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<div class="defun">
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— Built-in Function: const void * <b>__builtin___bnd_get_ptr_ubound</b> (<var>const void *q</var>)<var><a name="index-g_t_005f_005fbuiltin_005f_005f_005fbnd_005fget_005fptr_005fubound-3624"></a></var><br>
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<blockquote>
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<p>This built-in function returns the upper bound (which is a pointer) associated
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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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</blockquote></div>
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</body></html>
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