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238 lines
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HTML
238 lines
10 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 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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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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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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You have freedom to copy and modify this GNU Manual, like GNU
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>ARM Function Attributes (Using the GNU Compiler Collection (GCC))</title>
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<meta name="description" content="ARM Function Attributes (Using the GNU Compiler Collection (GCC))">
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<meta name="keywords" content="ARM Function Attributes (Using the GNU Compiler Collection (GCC))">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Function-Attributes.html#Function-Attributes" rel="up" title="Function Attributes">
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<link href="AVR-Function-Attributes.html#AVR-Function-Attributes" rel="next" title="AVR Function Attributes">
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<link href="ARC-Function-Attributes.html#ARC-Function-Attributes" rel="prev" title="ARC Function Attributes">
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</style>
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</head>
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<body lang="en">
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<a name="ARM-Function-Attributes"></a>
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<div class="header">
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<p>
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Next: <a href="AVR-Function-Attributes.html#AVR-Function-Attributes" accesskey="n" rel="next">AVR Function Attributes</a>, Previous: <a href="ARC-Function-Attributes.html#ARC-Function-Attributes" accesskey="p" rel="prev">ARC 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="ARM-Function-Attributes-1"></a>
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<h4 class="subsection">6.31.4 ARM Function Attributes</h4>
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<p>These function attributes are supported for ARM targets:
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</p>
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<dl compact="compact">
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<dt><code>interrupt</code></dt>
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<dd><a name="index-interrupt-function-attribute_002c-ARM"></a>
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<p>Use this attribute to indicate
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that the specified function is an interrupt handler. The compiler generates
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function entry and exit sequences suitable for use in an interrupt handler
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when this attribute is present.
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</p>
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<p>You can specify the kind of interrupt to be handled by
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adding an optional parameter to the interrupt attribute like this:
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</p>
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<div class="smallexample">
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<pre class="smallexample">void f () __attribute__ ((interrupt ("IRQ")));
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</pre></div>
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<p>Permissible values for this parameter are: <code>IRQ</code>, <code>FIQ</code>,
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<code>SWI</code>, <code>ABORT</code> and <code>UNDEF</code>.
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</p>
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<p>On ARMv7-M the interrupt type is ignored, and the attribute means the function
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may be called with a word-aligned stack pointer.
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</p>
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</dd>
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<dt><code>isr</code></dt>
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<dd><a name="index-isr-function-attribute_002c-ARM"></a>
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<p>Use this attribute on ARM to write Interrupt Service Routines. This is an
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alias to the <code>interrupt</code> attribute above.
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</p>
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</dd>
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<dt><code>long_call</code></dt>
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<dt><code>short_call</code></dt>
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<dd><a name="index-long_005fcall-function-attribute_002c-ARM"></a>
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<a name="index-short_005fcall-function-attribute_002c-ARM"></a>
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<a name="index-indirect-calls_002c-ARM"></a>
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<p>These attributes specify how a particular function is called.
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These attributes override the
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<samp>-mlong-calls</samp> (see <a href="ARM-Options.html#ARM-Options">ARM Options</a>)
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command-line switch and <code>#pragma long_calls</code> settings. For ARM, the
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<code>long_call</code> attribute indicates that the function might be far
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away from the call site and require a different (more expensive)
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calling sequence. The <code>short_call</code> attribute always places
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the offset to the function from the call site into the ‘<samp>BL</samp>’
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instruction directly.
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</p>
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</dd>
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<dt><code>naked</code></dt>
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<dd><a name="index-naked-function-attribute_002c-ARM"></a>
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<p>This attribute allows the compiler to construct the
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requisite function declaration, while allowing the body of the
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function to be assembly code. The specified function will not have
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prologue/epilogue sequences generated by the compiler. Only basic
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<code>asm</code> statements can safely be included in naked functions
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(see <a href="Basic-Asm.html#Basic-Asm">Basic Asm</a>). While using extended <code>asm</code> or a mixture of
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basic <code>asm</code> and C code may appear to work, they cannot be
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depended upon to work reliably and are not supported.
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</p>
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</dd>
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<dt><code>pcs</code></dt>
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<dd><a name="index-pcs-function-attribute_002c-ARM"></a>
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<p>The <code>pcs</code> attribute can be used to control the calling convention
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used for a function on ARM. The attribute takes an argument that specifies
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the calling convention to use.
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</p>
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<p>When compiling using the AAPCS ABI (or a variant of it) then valid
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values for the argument are <code>"aapcs"</code> and <code>"aapcs-vfp"</code>. In
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order to use a variant other than <code>"aapcs"</code> then the compiler must
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be permitted to use the appropriate co-processor registers (i.e., the
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VFP registers must be available in order to use <code>"aapcs-vfp"</code>).
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For example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">/* Argument passed in r0, and result returned in r0+r1. */
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double f2d (float) __attribute__((pcs("aapcs")));
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</pre></div>
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<p>Variadic functions always use the <code>"aapcs"</code> calling convention and
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the compiler rejects attempts to specify an alternative.
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</p>
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</dd>
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<dt><code>target (<var>options</var>)</code></dt>
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<dd><a name="index-target-function-attribute-1"></a>
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<p>As discussed in <a href="Common-Function-Attributes.html#Common-Function-Attributes">Common Function Attributes</a>, this attribute
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allows specification of target-specific compilation options.
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</p>
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<p>On ARM, the following options are allowed:
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</p>
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<dl compact="compact">
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<dt>‘<samp>thumb</samp>’</dt>
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<dd><a name="index-target_0028_0022thumb_0022_0029-function-attribute_002c-ARM"></a>
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<p>Force code generation in the Thumb (T16/T32) ISA, depending on the
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architecture level.
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</p>
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</dd>
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<dt>‘<samp>arm</samp>’</dt>
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<dd><a name="index-target_0028_0022arm_0022_0029-function-attribute_002c-ARM"></a>
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<p>Force code generation in the ARM (A32) ISA.
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</p>
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<p>Functions from different modes can be inlined in the caller’s mode.
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</p>
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</dd>
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<dt>‘<samp>fpu=</samp>’</dt>
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<dd><a name="index-target_0028_0022fpu_003d_0022_0029-function-attribute_002c-ARM"></a>
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<p>Specifies the fpu 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>-mfpu=</samp>
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command-line option.
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</p>
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</dd>
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<dt>‘<samp>arch=</samp>’</dt>
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<dd><a name="index-arch_003d-function-attribute_002c-ARM"></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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<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("arch=armv8-a+crc")))
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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>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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</dd>
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</dl>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="AVR-Function-Attributes.html#AVR-Function-Attributes" accesskey="n" rel="next">AVR Function Attributes</a>, Previous: <a href="ARC-Function-Attributes.html#ARC-Function-Attributes" accesskey="p" rel="prev">ARC 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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</body>
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