| <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> |
| <html> |
| <!-- Copyright (C) 1988-2015 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 5.2, http://www.gnu.org/software/texinfo/ --> |
| <head> |
| <title>GNU Compiler Collection (GCC) Internals: Anchored Addresses</title> |
| |
| <meta name="description" content="GNU Compiler Collection (GCC) Internals: Anchored Addresses"> |
| <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Anchored Addresses"> |
| <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="Option-Index.html#Option-Index" rel="index" title="Option Index"> |
| <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> |
| <link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros"> |
| <link href="Condition-Code.html#Condition-Code" rel="next" title="Condition Code"> |
| <link href="Addressing-Modes.html#Addressing-Modes" rel="prev" title="Addressing Modes"> |
| <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" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> |
| <a name="Anchored-Addresses"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Condition-Code.html#Condition-Code" accesskey="n" rel="next">Condition Code</a>, Previous: <a href="Addressing-Modes.html#Addressing-Modes" accesskey="p" rel="prev">Addressing Modes</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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> |
| </div> |
| <hr> |
| <a name="Anchored-Addresses-1"></a> |
| <h3 class="section">17.15 Anchored Addresses</h3> |
| <a name="index-anchored-addresses"></a> |
| <a name="index-_002dfsection_002danchors-1"></a> |
| |
| <p>GCC usually addresses every static object as a separate entity. |
| For example, if we have: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">static int a, b, c; |
| int foo (void) { return a + b + c; } |
| </pre></div> |
| |
| <p>the code for <code>foo</code> will usually calculate three separate symbolic |
| addresses: those of <code>a</code>, <code>b</code> and <code>c</code>. On some targets, |
| it would be better to calculate just one symbolic address and access |
| the three variables relative to it. The equivalent pseudocode would |
| be something like: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">int foo (void) |
| { |
| register int *xr = &x; |
| return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; |
| } |
| </pre></div> |
| |
| <p>(which isn’t valid C). We refer to shared addresses like <code>x</code> as |
| “section anchors”. Their use is controlled by <samp>-fsection-anchors</samp>. |
| </p> |
| <p>The hooks below describe the target properties that GCC needs to know |
| in order to make effective use of section anchors. It won’t use |
| section anchors at all unless either <code>TARGET_MIN_ANCHOR_OFFSET</code> |
| or <code>TARGET_MAX_ANCHOR_OFFSET</code> is set to a nonzero value. |
| </p> |
| <dl> |
| <dt><a name="index-TARGET_005fMIN_005fANCHOR_005fOFFSET"></a>Target Hook: <em>HOST_WIDE_INT</em> <strong>TARGET_MIN_ANCHOR_OFFSET</strong></dt> |
| <dd><p>The minimum offset that should be applied to a section anchor. |
| On most targets, it should be the smallest offset that can be |
| applied to a base register while still giving a legitimate address |
| for every mode. The default value is 0. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fMAX_005fANCHOR_005fOFFSET"></a>Target Hook: <em>HOST_WIDE_INT</em> <strong>TARGET_MAX_ANCHOR_OFFSET</strong></dt> |
| <dd><p>Like <code>TARGET_MIN_ANCHOR_OFFSET</code>, but the maximum (inclusive) |
| offset that should be applied to section anchors. The default |
| value is 0. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fASM_005fOUTPUT_005fANCHOR"></a>Target Hook: <em>void</em> <strong>TARGET_ASM_OUTPUT_ANCHOR</strong> <em>(rtx <var>x</var>)</em></dt> |
| <dd><p>Write the assembly code to define section anchor <var>x</var>, which is a |
| <code>SYMBOL_REF</code> for which ‘<samp>SYMBOL_REF_ANCHOR_P (<var>x</var>)</samp>’ is true. |
| The hook is called with the assembly output position set to the beginning |
| of <code>SYMBOL_REF_BLOCK (<var>x</var>)</code>. |
| </p> |
| <p>If <code>ASM_OUTPUT_DEF</code> is available, the hook’s default definition uses |
| it to define the symbol as ‘<samp>. + SYMBOL_REF_BLOCK_OFFSET (<var>x</var>)</samp>’. |
| If <code>ASM_OUTPUT_DEF</code> is not available, the hook’s default definition |
| is <code>NULL</code>, which disables the use of section anchors altogether. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-TARGET_005fUSE_005fANCHORS_005fFOR_005fSYMBOL_005fP"></a>Target Hook: <em>bool</em> <strong>TARGET_USE_ANCHORS_FOR_SYMBOL_P</strong> <em>(const_rtx <var>x</var>)</em></dt> |
| <dd><p>Return true if GCC should attempt to use anchors to access <code>SYMBOL_REF</code> |
| <var>x</var>. You can assume ‘<samp>SYMBOL_REF_HAS_BLOCK_INFO_P (<var>x</var>)</samp>’ and |
| ‘<samp>!SYMBOL_REF_ANCHOR_P (<var>x</var>)</samp>’. |
| </p> |
| <p>The default version is correct for most targets, but you might need to |
| intercept this hook to handle things like target-specific attributes |
| or target-specific sections. |
| </p></dd></dl> |
| |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Condition-Code.html#Condition-Code" accesskey="n" rel="next">Condition Code</a>, Previous: <a href="Addressing-Modes.html#Addressing-Modes" accesskey="p" rel="prev">Addressing Modes</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</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> |
| </div> |
| |
| |
| |
| </body> |
| </html> |
