| <!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: Portability</title> |
| |
| <meta name="description" content="GNU Compiler Collection (GCC) Internals: Portability"> |
| <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Portability"> |
| <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="index.html#Top" rel="up" title="Top"> |
| <link href="Interface.html#Interface" rel="next" title="Interface"> |
| <link href="Contributing.html#Contributing" rel="prev" title="Contributing"> |
| <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="Portability"></a> |
| <div class="header"> |
| <p> |
| Next: <a href="Interface.html#Interface" accesskey="n" rel="next">Interface</a>, Previous: <a href="Contributing.html#Contributing" accesskey="p" rel="prev">Contributing</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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="GCC-and-Portability"></a> |
| <h2 class="chapter">2 GCC and Portability</h2> |
| <a name="index-portability"></a> |
| <a name="index-GCC-and-portability"></a> |
| |
| <p>GCC itself aims to be portable to any machine where <code>int</code> is at least |
| a 32-bit type. It aims to target machines with a flat (non-segmented) byte |
| addressed data address space (the code address space can be separate). |
| Target ABIs may have 8, 16, 32 or 64-bit <code>int</code> type. <code>char</code> |
| can be wider than 8 bits. |
| </p> |
| <p>GCC gets most of the information about the target machine from a machine |
| description which gives an algebraic formula for each of the machine’s |
| instructions. This is a very clean way to describe the target. But when |
| the compiler needs information that is difficult to express in this |
| fashion, ad-hoc parameters have been defined for machine descriptions. |
| The purpose of portability is to reduce the total work needed on the |
| compiler; it was not of interest for its own sake. |
| </p> |
| <a name="index-endianness"></a> |
| <a name="index-autoincrement-addressing_002c-availability"></a> |
| <a name="index-abort"></a> |
| <p>GCC does not contain machine dependent code, but it does contain code |
| that depends on machine parameters such as endianness (whether the most |
| significant byte has the highest or lowest address of the bytes in a word) |
| and the availability of autoincrement addressing. In the RTL-generation |
| pass, it is often necessary to have multiple strategies for generating code |
| for a particular kind of syntax tree, strategies that are usable for different |
| combinations of parameters. Often, not all possible cases have been |
| addressed, but only the common ones or only the ones that have been |
| encountered. As a result, a new target may require additional |
| strategies. You will know |
| if this happens because the compiler will call <code>abort</code>. Fortunately, |
| the new strategies can be added in a machine-independent fashion, and will |
| affect only the target machines that need them. |
| </p> |
| <hr> |
| <div class="header"> |
| <p> |
| Next: <a href="Interface.html#Interface" accesskey="n" rel="next">Interface</a>, Previous: <a href="Contributing.html#Contributing" accesskey="p" rel="prev">Contributing</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</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> |
