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<a name="AArch64-Function-Attributes"></a>
<div class="header">
<p>
Next: <a href="AMD-GCN-Function-Attributes.html#AMD-GCN-Function-Attributes" accesskey="n" rel="next">AMD GCN Function Attributes</a>, Previous: <a href="Common-Function-Attributes.html#Common-Function-Attributes" accesskey="p" rel="prev">Common Function Attributes</a>, Up: <a href="Function-Attributes.html#Function-Attributes" accesskey="u" rel="up">Function Attributes</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>
</div>
<hr>
<a name="AArch64-Function-Attributes-1"></a>
<h4 class="subsection">6.33.2 AArch64 Function Attributes</h4>

<p>The following target-specific function attributes are available for the
AArch64 target.  For the most part, these options mirror the behavior of
similar command-line options (see <a href="AArch64-Options.html#AArch64-Options">AArch64 Options</a>), but on a
per-function basis.
</p>
<dl compact="compact">
<dt><code>general-regs-only</code></dt>
<dd><a name="index-general_002dregs_002donly-function-attribute_002c-AArch64"></a>
<p>Indicates that no floating-point or Advanced SIMD registers should be
used when generating code for this function.  If the function explicitly
uses floating-point code, then the compiler gives an error.  This is
the same behavior as that of the command-line option
<samp>-mgeneral-regs-only</samp>.
</p>
</dd>
<dt><code>fix-cortex-a53-835769</code></dt>
<dd><a name="index-fix_002dcortex_002da53_002d835769-function-attribute_002c-AArch64"></a>
<p>Indicates that the workaround for the Cortex-A53 erratum 835769 should be
applied to this function.  To explicitly disable the workaround for this
function specify the negated form: <code>no-fix-cortex-a53-835769</code>.
This corresponds to the behavior of the command line options
<samp>-mfix-cortex-a53-835769</samp> and <samp>-mno-fix-cortex-a53-835769</samp>.
</p>
</dd>
<dt><code>cmodel=</code></dt>
<dd><a name="index-cmodel_003d-function-attribute_002c-AArch64"></a>
<p>Indicates that code should be generated for a particular code model for
this function.  The behavior and permissible arguments are the same as
for the command line option <samp>-mcmodel=</samp>.
</p>
</dd>
<dt><code>strict-align</code></dt>
<dt><code>no-strict-align</code></dt>
<dd><a name="index-strict_002dalign-function-attribute_002c-AArch64"></a>
<p><code>strict-align</code> indicates that the compiler should not assume that unaligned
memory references are handled by the system.  To allow the compiler to assume
that aligned memory references are handled by the system, the inverse attribute
<code>no-strict-align</code> can be specified.  The behavior is same as for the
command-line option <samp>-mstrict-align</samp> and <samp>-mno-strict-align</samp>.
</p>
</dd>
<dt><code>omit-leaf-frame-pointer</code></dt>
<dd><a name="index-omit_002dleaf_002dframe_002dpointer-function-attribute_002c-AArch64"></a>
<p>Indicates that the frame pointer should be omitted for a leaf function call.
To keep the frame pointer, the inverse attribute
<code>no-omit-leaf-frame-pointer</code> can be specified.  These attributes have
the same behavior as the command-line options <samp>-momit-leaf-frame-pointer</samp>
and <samp>-mno-omit-leaf-frame-pointer</samp>.
</p>
</dd>
<dt><code>tls-dialect=</code></dt>
<dd><a name="index-tls_002ddialect_003d-function-attribute_002c-AArch64"></a>
<p>Specifies the TLS dialect to use for this function.  The behavior and
permissible arguments are the same as for the command-line option
<samp>-mtls-dialect=</samp>.
</p>
</dd>
<dt><code>arch=</code></dt>
<dd><a name="index-arch_003d-function-attribute_002c-AArch64"></a>
<p>Specifies the architecture version and architectural extensions to use
for this function.  The behavior and permissible arguments are the same as
for the <samp>-march=</samp> command-line option.
</p>
</dd>
<dt><code>tune=</code></dt>
<dd><a name="index-tune_003d-function-attribute_002c-AArch64"></a>
<p>Specifies the core for which to tune the performance of this function.
The behavior and permissible arguments are the same as for the <samp>-mtune=</samp>
command-line option.
</p>
</dd>
<dt><code>cpu=</code></dt>
<dd><a name="index-cpu_003d-function-attribute_002c-AArch64"></a>
<p>Specifies the core for which to tune the performance of this function and also
whose architectural features to use.  The behavior and valid arguments are the
same as for the <samp>-mcpu=</samp> command-line option.
</p>
</dd>
<dt><code>sign-return-address</code></dt>
<dd><a name="index-sign_002dreturn_002daddress-function-attribute_002c-AArch64"></a>
<p>Select the function scope on which return address signing will be applied.  The
behavior and permissible arguments are the same as for the command-line option
<samp>-msign-return-address=</samp>.  The default value is <code>none</code>.  This
attribute is deprecated.  The <code>branch-protection</code> attribute should
be used instead.
</p>
</dd>
<dt><code>branch-protection</code></dt>
<dd><a name="index-branch_002dprotection-function-attribute_002c-AArch64"></a>
<p>Select the function scope on which branch protection will be applied.  The
behavior and permissible arguments are the same as for the command-line option
<samp>-mbranch-protection=</samp>.  The default value is <code>none</code>.
</p>
</dd>
<dt><code>outline-atomics</code></dt>
<dd><a name="index-outline_002datomics-function-attribute_002c-AArch64"></a>
<p>Enable or disable calls to out-of-line helpers to implement atomic operations.
This corresponds to the behavior of the command line options
<samp>-moutline-atomics</samp> and <samp>-mno-outline-atomics</samp>.
</p>
</dd>
</dl>

<p>The above target attributes can be specified as follows:
</p>
<div class="smallexample">
<pre class="smallexample">__attribute__((target(&quot;<var>attr-string</var>&quot;)))
int
f (int a)
{
  return a + 5;
}
</pre></div>

<p>where <code><var>attr-string</var></code> is one of the attribute strings specified above.
</p>
<p>Additionally, the architectural extension string may be specified on its
own.  This can be used to turn on and off particular architectural extensions
without having to specify a particular architecture version or core.  Example:
</p>
<div class="smallexample">
<pre class="smallexample">__attribute__((target(&quot;+crc+nocrypto&quot;)))
int
foo (int a)
{
  return a + 5;
}
</pre></div>

<p>In this example <code>target(&quot;+crc+nocrypto&quot;)</code> enables the <code>crc</code>
extension and disables the <code>crypto</code> extension for the function <code>foo</code>
without modifying an existing <samp>-march=</samp> or <samp>-mcpu</samp> option.
</p>
<p>Multiple target function attributes can be specified by separating them with
a comma.  For example:
</p><div class="smallexample">
<pre class="smallexample">__attribute__((target(&quot;arch=armv8-a+crc+crypto,tune=cortex-a53&quot;)))
int
foo (int a)
{
  return a + 5;
}
</pre></div>

<p>is valid and compiles function <code>foo</code> for ARMv8-A with <code>crc</code>
and <code>crypto</code> extensions and tunes it for <code>cortex-a53</code>.
</p>
<a name="Inlining-rules"></a>
<h4 class="subsubsection">6.33.2.1 Inlining rules</h4>
<p>Specifying target attributes on individual functions or performing link-time
optimization across translation units compiled with different target options
can affect function inlining rules:
</p>
<p>In particular, a caller function can inline a callee function only if the
architectural features available to the callee are a subset of the features
available to the caller.
For example: A function <code>foo</code> compiled with <samp>-march=armv8-a+crc</samp>,
or tagged with the equivalent <code>arch=armv8-a+crc</code> attribute,
can inline a function <code>bar</code> compiled with <samp>-march=armv8-a+nocrc</samp>
because the all the architectural features that function <code>bar</code> requires
are available to function <code>foo</code>.  Conversely, function <code>bar</code> cannot
inline function <code>foo</code>.
</p>
<p>Additionally inlining a function compiled with <samp>-mstrict-align</samp> into a
function compiled without <code>-mstrict-align</code> is not allowed.
However, inlining a function compiled without <samp>-mstrict-align</samp> into a
function compiled with <samp>-mstrict-align</samp> is allowed.
</p>
<p>Note that CPU tuning options and attributes such as the <samp>-mcpu=</samp>,
<samp>-mtune=</samp> do not inhibit inlining unless the CPU specified by the
<samp>-mcpu=</samp> option or the <code>cpu=</code> attribute conflicts with the
architectural feature rules specified above.
</p>
<hr>
<div class="header">
<p>
Next: <a href="AMD-GCN-Function-Attributes.html#AMD-GCN-Function-Attributes" accesskey="n" rel="next">AMD GCN Function Attributes</a>, Previous: <a href="Common-Function-Attributes.html#Common-Function-Attributes" accesskey="p" rel="prev">Common Function Attributes</a>, Up: <a href="Function-Attributes.html#Function-Attributes" accesskey="u" rel="up">Function Attributes</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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