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123 lines
6.1 KiB
HTML
123 lines
6.1 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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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Libgloss (Embed with GNU)</title>
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<meta name="description" content="Libgloss (Embed with GNU)">
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<meta name="keywords" content="Libgloss (Embed with GNU)">
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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="leds_002ec.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="index.html#Top" rel="up" title="Top">
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<link href="Supported-targets.html#Supported-targets" rel="next" title="Supported targets">
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<link href="index.html#Top" rel="prev" title="Top">
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</head>
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<body lang="en">
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<a name="Libgloss"></a>
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<div class="header">
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<p>
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Next: <a href="GCC.html#GCC" accesskey="n" rel="next">GCC</a>, Previous: <a href="index.html#Top" accesskey="p" rel="prev">Top</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="leds_002ec.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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</div>
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<hr>
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<a name="Libgloss-1"></a>
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<h2 class="chapter">1 Libgloss</h2>
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<p>Libgloss is a library for all the details that usually get glossed over.
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This library refers to things like startup code, and usually I/O support
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for <code>gcc</code> and <code>C library</code>. The C library used through out
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this manual is <code>newlib</code>. Newlib is a ANSI conforming C library
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developed by Cygnus Support. Libgloss could easily be made to
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support other C libraries, and it can be used standalone as well. The
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standalone configuration is typically used when bringing up new
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hardware, or on small systems.
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</p>
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<p>For a long time, these details were part of newlib. This approach worked
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well when a complete tool chain only had to support one system. A tool
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chain refers to the series of compiler passes required to produce a
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binary file that will run on an embedded system. For C, the passes are
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cpp, gcc, gas, ld. Cpp is the preprocessor, which process all the header
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files and macros. Gcc is the compiler, which produces assembler from the
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processed C files. Gas assembles the code into object files, and then ld
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combines the object files and binds the code to addresses and produces
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the final executable image.
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</p>
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<p>Most of the time a tool chain does only have to support one target
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execution environment. An example of this would be a tool chain for the
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AMD 29k processor family. All of the execution environments for this
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processor have the same interface, the same memory map, and the same
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I/O code. In this case all of the support code is under newlib/libc/sys.
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Libgloss’s creation was forced initially because of the <code>cpu32</code>
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processor family. There are many different execution environments for
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this line, and they vary wildly. newlib itself has only a few
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dependencies that it needs for each target. These are explained later in
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this doc. The hardware dependent part of newlib was reorganized into a
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separate directory structure within newlib called the stub dirs. It was
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initially called this because most of the routines newlib needs for a
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target were simple stubs that do nothing, but return a value to the
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application. They only exist so the linker can produce a final
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executable image. This work was done during the early part of 1993.
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</p>
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<p>After a while it became apparent that this approach of isolating the
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hardware and systems files together made sense. Around this same time
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the stub dirs were made to run standalone, mostly so it could also be
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used to support GDB’s remote debugging needs. At this time it was
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decided to move the stub dirs out of newlib and into it’s own separate
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library so it could be used standalone, and be included in various other
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GNU tools without having to bring in all of newlib, which is large. The
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new library is called Libgloss, for Gnu Low-level OS support.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Supported-targets.html#Supported-targets" accesskey="1">Supported targets</a>:</td><td> </td><td align="left" valign="top">What targets libgloss currently
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supports.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Building-libgloss.html#Building-libgloss" accesskey="2">Building libgloss</a>:</td><td> </td><td align="left" valign="top">How to configure and built libgloss
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for a target.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Board-support.html#Board-support" accesskey="3">Board support</a>:</td><td> </td><td align="left" valign="top">How to add support for a new board.
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="GCC.html#GCC" accesskey="n" rel="next">GCC</a>, Previous: <a href="index.html#Top" accesskey="p" rel="prev">Top</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="leds_002ec.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>]</p>
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</div>
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</body>
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</html>
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