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<a name="Stack-smashing-protection"></a>
<h4 class="subsection">18.9.15 Stack smashing protection</h4>
<a name="index-stack-smashing-protection"></a>

<dl>
<dt><a name="index-TARGET_005fSTACK_005fPROTECT_005fGUARD"></a>Target Hook: <em>tree</em> <strong>TARGET_STACK_PROTECT_GUARD</strong> <em>(void)</em></dt>
<dd><p>This hook returns a <code>DECL</code> node for the external variable to use
for the stack protection guard.  This variable is initialized by the
runtime to some random value and is used to initialize the guard value
that is placed at the top of the local stack frame.  The type of this
variable must be <code>ptr_type_node</code>.
</p>
<p>The default version of this hook creates a variable called
&lsquo;<samp>__stack_chk_guard</samp>&rsquo;, which is normally defined in <samp>libgcc2.c</samp>.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSTACK_005fPROTECT_005fFAIL"></a>Target Hook: <em>tree</em> <strong>TARGET_STACK_PROTECT_FAIL</strong> <em>(void)</em></dt>
<dd><p>This hook returns a <code>CALL_EXPR</code> that alerts the runtime that the
stack protect guard variable has been modified.  This expression should
involve a call to a <code>noreturn</code> function.
</p>
<p>The default version of this hook invokes a function called
&lsquo;<samp>__stack_chk_fail</samp>&rsquo;, taking no arguments.  This function is
normally defined in <samp>libgcc2.c</samp>.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSTACK_005fPROTECT_005fRUNTIME_005fENABLED_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_STACK_PROTECT_RUNTIME_ENABLED_P</strong> <em>(void)</em></dt>
<dd><p>Returns true if the target wants GCC&rsquo;s default stack protect runtime support, otherwise return false.  The default implementation always returns true.
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fSUPPORTS_005fSPLIT_005fSTACK"></a>Common Target Hook: <em>bool</em> <strong>TARGET_SUPPORTS_SPLIT_STACK</strong> <em>(bool <var>report</var>, struct gcc_options *<var>opts</var>)</em></dt>
<dd><p>Whether this target supports splitting the stack when the options described in <var>opts</var> have been passed.  This is called after options have been parsed, so the target may reject splitting the stack in some configurations.  The default version of this hook returns false.  If <var>report</var> is true, this function may issue a warning or error; if <var>report</var> is false, it must simply return a value
</p></dd></dl>

<dl>
<dt><a name="index-TARGET_005fGET_005fVALID_005fOPTION_005fVALUES"></a>Common Target Hook: <em>vec&lt;const char *&gt;</em> <strong>TARGET_GET_VALID_OPTION_VALUES</strong> <em>(int <var>option_code</var>, const char *<var>prefix</var>)</em></dt>
<dd><p>The hook is used for options that have a non-trivial list of possible option values.  OPTION_CODE is option code of opt_code enum type.  PREFIX is used for bash completion and allows an implementation to return more specific completion based on the prefix.  All string values should be allocated from heap memory and consumers should release them.  The result will be pruned to cases with PREFIX if not NULL.
</p></dd></dl>

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