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105 lines
4.7 KiB
HTML
105 lines
4.7 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>Overview (Embed with GNU)</title>
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<meta name="description" content="Overview (Embed with GNU)">
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<meta name="keywords" content="Overview (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="GCC.html#GCC" rel="up" title="GCC">
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<link href="Options.html#Options" rel="next" title="Options">
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<link href="GCC.html#GCC" rel="prev" title="GCC">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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ul.no-bullet {list-style: none}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Overview"></a>
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<div class="header">
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<p>
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Next: <a href="Options.html#Options" accesskey="n" rel="next">Options</a>, Up: <a href="GCC.html#GCC" accesskey="u" rel="up">GCC</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="Compilation-passes"></a>
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<h3 class="section">2.1 Compilation passes</h3>
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<p>GCC by itself only compiles the C or C++ code into assembler. Typically
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GCC invokes all the passes required for you. These passes are cpp, cc1,
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gas, ld. <code>cpp</code> is the C preprocessor. This will merge in the
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include files, expand all macros definitions, and process all the
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<code>#ifdef</code> sections. To see the output of ccp, invoke gcc with the
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<code>-E</code> option, and the preprocessed file will be printed on the
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stdout. cc1 is the actual compiler pass that produces the assembler for
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the processed file. GCC is actually only a driver program for all the
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compiler passes. It will format command line options for the other passes.
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The usual command line GCC uses for the final link phase will have LD
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link in the startup code and additional libraries by default.
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</p>
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<p>GNU AS started it’s life to only function as a compiler pass, but
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these days it can also be used as a source level assembler. When used as
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a source level assembler, it has a companion assembler preprocessor
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called <code>gasp</code>. This has a syntax similar to most other assembler
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macros packages. GAS emits a relocatable object file from the assembler
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source. The object file contains the executable part of the application,
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and debug symbols.
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</p>
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<p>LD is responsible for resolving the addresses and symbols to something
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that will be fully self-contained. Some RTOS’s use relocatable object
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file formats like <code>a.out</code>, but more commonly the final image will
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only use absolute addresses for symbols. This enables code to be burned
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into PROMS as well. Although LD can produce an executable image, there
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is usually a hidden object file called <code>crt0.o</code> that is required as
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startup code. With this startup code and a memory map, the executable
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image will actually run on the target environment. <a href="Crt0.html#Crt0">Startup
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Files</a>.
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</p>
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<p>The startup code usually defines a special symbol like <code>_start</code>
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that is the default base address for the application, and the first
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symbol in the executable image. If you plan to use any routines from the
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standard C library, you’ll also need to implement the functions that
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this library is dependent on. <a href="Libraries.html#Libraries">Porting Newlib</a>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Options.html#Options" accesskey="n" rel="next">Options</a>, Up: <a href="GCC.html#GCC" accesskey="u" rel="up">GCC</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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