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<title>Using the GNU Compiler Collection (GCC): AArch64 Function Attributes</title>
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<a name="AArch64-Function-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="ARC-Function-Attributes.html#ARC-Function-Attributes" accesskey="n" rel="next">ARC 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> [<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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</div>
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<hr>
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<a name="AArch64-Function-Attributes-1"></a>
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<h4 class="subsection">6.31.2 AArch64 Function Attributes</h4>
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<p>The following target-specific function attributes are available for the
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AArch64 target. For the most part, these options mirror the behavior of
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similar command-line options (see <a href="AArch64-Options.html#AArch64-Options">AArch64 Options</a>), but on a
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per-function basis.
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</p>
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<dl compact="compact">
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<dt><code>general-regs-only</code></dt>
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<dd><a name="index-general_002dregs_002donly-function-attribute_002c-AArch64"></a>
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<p>Indicates that no floating-point or Advanced SIMD registers should be
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used when generating code for this function. If the function explicitly
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uses floating-point code, then the compiler gives an error. This is
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the same behavior as that of the command-line option
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<samp>-mgeneral-regs-only</samp>.
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</p>
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</dd>
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<dt><code>fix-cortex-a53-835769</code></dt>
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<dd><a name="index-fix_002dcortex_002da53_002d835769-function-attribute_002c-AArch64"></a>
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<p>Indicates that the workaround for the Cortex-A53 erratum 835769 should be
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applied to this function. To explicitly disable the workaround for this
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function specify the negated form: <code>no-fix-cortex-a53-835769</code>.
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This corresponds to the behavior of the command line options
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<samp>-mfix-cortex-a53-835769</samp> and <samp>-mno-fix-cortex-a53-835769</samp>.
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</p>
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</dd>
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<dt><code>cmodel=</code></dt>
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<dd><a name="index-cmodel_003d-function-attribute_002c-AArch64"></a>
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<p>Indicates that code should be generated for a particular code model for
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this function. The behavior and permissible arguments are the same as
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for the command line option <samp>-mcmodel=</samp>.
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</p>
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</dd>
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<dt><code>strict-align</code></dt>
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<dd><a name="index-strict_002dalign-function-attribute_002c-AArch64"></a>
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<p>Indicates that the compiler should not assume that unaligned memory references
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are handled by the system. The behavior is the same as for the command-line
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option <samp>-mstrict-align</samp>.
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</p>
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</dd>
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<dt><code>omit-leaf-frame-pointer</code></dt>
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<dd><a name="index-omit_002dleaf_002dframe_002dpointer-function-attribute_002c-AArch64"></a>
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<p>Indicates that the frame pointer should be omitted for a leaf function call.
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To keep the frame pointer, the inverse attribute
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<code>no-omit-leaf-frame-pointer</code> can be specified. These attributes have
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the same behavior as the command-line options <samp>-momit-leaf-frame-pointer</samp>
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and <samp>-mno-omit-leaf-frame-pointer</samp>.
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</p>
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</dd>
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<dt><code>tls-dialect=</code></dt>
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<dd><a name="index-tls_002ddialect_003d-function-attribute_002c-AArch64"></a>
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<p>Specifies the TLS dialect to use for this function. The behavior and
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permissible arguments are the same as for the command-line option
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<samp>-mtls-dialect=</samp>.
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</p>
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</dd>
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<dt><code>arch=</code></dt>
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<dd><a name="index-arch_003d-function-attribute_002c-AArch64"></a>
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<p>Specifies the architecture version and architectural extensions to use
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for this function. The behavior and permissible arguments are the same as
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for the <samp>-march=</samp> command-line option.
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</p>
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</dd>
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<dt><code>tune=</code></dt>
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<dd><a name="index-tune_003d-function-attribute_002c-AArch64"></a>
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<p>Specifies the core for which to tune the performance of this function.
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The behavior and permissible arguments are the same as for the <samp>-mtune=</samp>
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command-line option.
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</p>
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</dd>
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<dt><code>cpu=</code></dt>
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<dd><a name="index-cpu_003d-function-attribute_002c-AArch64"></a>
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<p>Specifies the core for which to tune the performance of this function and also
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whose architectural features to use. The behavior and valid arguments are the
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same as for the <samp>-mcpu=</samp> command-line option.
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</p>
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</dd>
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</dl>
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<p>The above target attributes can be specified as follows:
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</p>
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<div class="smallexample">
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<pre class="smallexample">__attribute__((target("<var>attr-string</var>")))
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int
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f (int a)
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{
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return a + 5;
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}
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</pre></div>
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<p>where <code><var>attr-string</var></code> is one of the attribute strings specified above.
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</p>
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<p>Additionally, the architectural extension string may be specified on its
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own. This can be used to turn on and off particular architectural extensions
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without having to specify a particular architecture version or core. Example:
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</p>
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<div class="smallexample">
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<pre class="smallexample">__attribute__((target("+crc+nocrypto")))
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int
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foo (int a)
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{
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return a + 5;
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}
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</pre></div>
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<p>In this example <code>target("+crc+nocrypto")</code> enables the <code>crc</code>
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extension and disables the <code>crypto</code> extension for the function <code>foo</code>
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without modifying an existing <samp>-march=</samp> or <samp>-mcpu</samp> option.
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</p>
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<p>Multiple target function attributes can be specified by separating them with
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a comma. For example:
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</p><div class="smallexample">
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<pre class="smallexample">__attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53")))
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int
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foo (int a)
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{
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return a + 5;
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}
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</pre></div>
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<p>is valid and compiles function <code>foo</code> for ARMv8-A with <code>crc</code>
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and <code>crypto</code> extensions and tunes it for <code>cortex-a53</code>.
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</p>
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<a name="Inlining-rules"></a>
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<h4 class="subsubsection">6.31.2.1 Inlining rules</h4>
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<p>Specifying target attributes on individual functions or performing link-time
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optimization across translation units compiled with different target options
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can affect function inlining rules:
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</p>
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<p>In particular, a caller function can inline a callee function only if the
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architectural features available to the callee are a subset of the features
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available to the caller.
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For example: A function <code>foo</code> compiled with <samp>-march=armv8-a+crc</samp>,
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or tagged with the equivalent <code>arch=armv8-a+crc</code> attribute,
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can inline a function <code>bar</code> compiled with <samp>-march=armv8-a+nocrc</samp>
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because the all the architectural features that function <code>bar</code> requires
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are available to function <code>foo</code>. Conversely, function <code>bar</code> cannot
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inline function <code>foo</code>.
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</p>
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<p>Additionally inlining a function compiled with <samp>-mstrict-align</samp> into a
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function compiled without <code>-mstrict-align</code> is not allowed.
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However, inlining a function compiled without <samp>-mstrict-align</samp> into a
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function compiled with <samp>-mstrict-align</samp> is allowed.
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</p>
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<p>Note that CPU tuning options and attributes such as the <samp>-mcpu=</samp>,
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<samp>-mtune=</samp> do not inhibit inlining unless the CPU specified by the
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<samp>-mcpu=</samp> option or the <code>cpu=</code> attribute conflicts with the
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architectural feature rules specified above.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="ARC-Function-Attributes.html#ARC-Function-Attributes" accesskey="n" rel="next">ARC 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> [<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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