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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gcc/Qualifiers-implementation.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
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diff --git a/share/doc/gcc/Qualifiers-implementation.html b/share/doc/gcc/Qualifiers-implementation.html new file mode 100644 index 0000000..68517ce --- /dev/null +++ b/share/doc/gcc/Qualifiers-implementation.html @@ -0,0 +1,138 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Qualifiers implementation</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Qualifiers implementation"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Qualifiers implementation"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C-Implementation.html#C-Implementation" rel="up" title="C Implementation"> +<link href="Declarators-implementation.html#Declarators-implementation" rel="next" title="Declarators implementation"> +<link href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" rel="previous" title="Structures unions enumerations and bit-fields implementation"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Qualifiers-implementation"></a> +<div class="header"> +<p> +Next: <a href="Declarators-implementation.html#Declarators-implementation" accesskey="n" rel="next">Declarators implementation</a>, Previous: <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" accesskey="p" rel="previous">Structures unions enumerations and bit-fields implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Qualifiers"></a> +<h3 class="section">4.10 Qualifiers</h3> + +<ul> +<li> <cite>What constitutes an access to an object that has volatile-qualified +type (C90 6.5.3, C99 and C11 6.7.3).</cite> + +<p>Such an object is normally accessed by pointers and used for accessing +hardware. In most expressions, it is intuitively obvious what is a read +and what is a write. For example +</p> +<div class="smallexample"> +<pre class="smallexample">volatile int *dst = <var>somevalue</var>; +volatile int *src = <var>someothervalue</var>; +*dst = *src; +</pre></div> + +<p>will cause a read of the volatile object pointed to by <var>src</var> and store the +value into the volatile object pointed to by <var>dst</var>. There is no +guarantee that these reads and writes are atomic, especially for objects +larger than <code>int</code>. +</p> +<p>However, if the volatile storage is not being modified, and the value of +the volatile storage is not used, then the situation is less obvious. +For example +</p> +<div class="smallexample"> +<pre class="smallexample">volatile int *src = <var>somevalue</var>; +*src; +</pre></div> + +<p>According to the C standard, such an expression is an rvalue whose type +is the unqualified version of its original type, i.e. <code>int</code>. Whether +GCC interprets this as a read of the volatile object being pointed to or +only as a request to evaluate the expression for its side effects depends +on this type. +</p> +<p>If it is a scalar type, or on most targets an aggregate type whose only +member object is of a scalar type, or a union type whose member objects +are of scalar types, the expression is interpreted by GCC as a read of +the volatile object; in the other cases, the expression is only evaluated +for its side effects. +</p> +<p>When an object of an aggregate type, with the same size and alignment as a +scalar type <code>S</code>, is the subject of a volatile access by an assignment +expression or an atomic function, the access to it is performed as if the +object’s declared type were <code>volatile S</code>. +</p> +</li></ul> + +<hr> +<div class="header"> +<p> +Next: <a href="Declarators-implementation.html#Declarators-implementation" accesskey="n" rel="next">Declarators implementation</a>, Previous: <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" accesskey="p" rel="previous">Structures unions enumerations and bit-fields implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |