visus
/
toolchain-gcc-arm-embedded


			
							<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This file documents the BFD library.

Copyright (C) 1991-2020 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 "GNU General Public License" and "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 6.5, http://www.gnu.org/software/texinfo/ -->
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Symbol-table (Untitled Document)</title>

<meta name="description" content="Symbol-table (Untitled Document)">
<meta name="keywords" content="Symbol-table (Untitled Document)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
<link href="index.html#Top" rel="start" title="Top">
<link href="BFD-Index.html#BFD-Index" rel="index" title="BFD Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
<link href="mmo.html#mmo" rel="up" title="mmo">
<link href="mmo-section-mapping.html#mmo-section-mapping" rel="next" title="mmo section mapping">
<link href="File-layout.html#File-layout" rel="prev" title="File layout">
<style type="text/css">
<!--
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
div.lisp {margin-left: 3.2em}
div.smalldisplay {margin-left: 3.2em}
div.smallexample {margin-left: 3.2em}
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.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
ul.no-bullet {list-style: none}
-->
</style>


</head>

<body lang="en">
<a name="Symbol_002dtable"></a>
<div class="header">
<p>
Next: <a href="mmo-section-mapping.html#mmo-section-mapping" accesskey="n" rel="next">mmo section mapping</a>, Previous: <a href="File-layout.html#File-layout" accesskey="p" rel="prev">File layout</a>, Up: <a href="mmo.html#mmo" accesskey="u" rel="up">mmo</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Symbol-table-format"></a>
<h4 class="subsection">3.5.2 Symbol table format</h4>
<p>From mmixal.w (or really, the generated mmixal.tex) in the
MMIXware package which also contains the <code>mmix</code> simulator:
&ldquo;Symbols are stored and retrieved by means of a &lsquo;<samp>ternary
search trie</samp>&rsquo;, following ideas of Bentley and Sedgewick. (See
ACM&ndash;SIAM Symp. on Discrete Algorithms &lsquo;<samp>8</samp>&rsquo; (1997), 360&ndash;369;
R.Sedgewick, &lsquo;<samp>Algorithms in C</samp>&rsquo; (Reading, Mass.
Addison&ndash;Wesley, 1998), &lsquo;<samp>15.4</samp>&rsquo;.)  Each trie node stores a
character, and there are branches to subtries for the cases where
a given character is less than, equal to, or greater than the
character in the trie.  There also is a pointer to a symbol table
entry if a symbol ends at the current node.&rdquo;
</p>
<p>So it&rsquo;s a tree encoded as a stream of bytes.  The stream of bytes
acts on a single virtual global symbol, adding and removing
characters and signalling complete symbol points.  Here, we read
the stream and create symbols at the completion points.
</p>
<p>First, there&rsquo;s a control byte <code>m</code>.  If any of the listed bits
in <code>m</code> is nonzero, we execute what stands at the right, in
the listed order:
</p>
<div class="example">
<pre class="example"> (MMO3_LEFT)
 0x40 - Traverse left trie.
        (Read a new command byte and recurse.)

 (MMO3_SYMBITS)
 0x2f - Read the next byte as a character and store it in the
        current character position; increment character position.
        Test the bits of <code>m</code>:

        (MMO3_WCHAR)
        0x80 - The character is 16-bit (so read another byte,
               merge into current character.

        (MMO3_TYPEBITS)
        0xf  - We have a complete symbol; parse the type, value
               and serial number and do what should be done
               with a symbol.  The type and length information
               is in j = (m &amp; 0xf).

               (MMO3_REGQUAL_BITS)
               j == 0xf: A register variable.  The following
                         byte tells which register.
               j &lt;= 8:   An absolute symbol.  Read j bytes as the
                         big-endian number the symbol equals.
                         A j = 2 with two zero bytes denotes an
                         unknown symbol.
               j &gt; 8:    As with j &lt;= 8, but add (0x20 &lt;&lt; 56)
                         to the value in the following j - 8
                         bytes.

               Then comes the serial number, as a variant of
               uleb128, but better named ubeb128:
               Read bytes and shift the previous value left 7
               (multiply by 128).  Add in the new byte, repeat
               until a byte has bit 7 set.  The serial number
               is the computed value minus 128.

        (MMO3_MIDDLE)
        0x20 - Traverse middle trie.  (Read a new command byte
               and recurse.)  Decrement character position.

 (MMO3_RIGHT)
 0x10 - Traverse right trie.  (Read a new command byte and
        recurse.)
</pre></div>

<p>Let&rsquo;s look again at the <code>lop_stab</code> for the trivial file
(see <a href="File-layout.html#File-layout">File layout</a>).
</p>
<div class="example">
<pre class="example"> 0x980b0000 - lop_stab for &quot;:Main&quot; = 0, serial 1.
 0x203a4040
 0x10404020
 0x4d206120
 0x69016e00
 0x81000000
</pre></div>

<p>This forms the trivial trie (note that the path between &ldquo;:&rdquo; and
&ldquo;M&rdquo; is redundant):
</p>
<div class="example">
<pre class="example"> 203a     &quot;:&quot;
 40       /
 40      /
 10      \
 40      /
 40     /
 204d  &quot;M&quot;
 2061  &quot;a&quot;
 2069  &quot;i&quot;
 016e  &quot;n&quot; is the last character in a full symbol, and
       with a value represented in one byte.
 00    The value is 0.
 81    The serial number is 1.
</pre></div>

<hr>
<div class="header">
<p>
Next: <a href="mmo-section-mapping.html#mmo-section-mapping" accesskey="n" rel="next">mmo section mapping</a>, Previous: <a href="File-layout.html#File-layout" accesskey="p" rel="prev">File layout</a>, Up: <a href="mmo.html#mmo" accesskey="u" rel="up">mmo</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="BFD-Index.html#BFD-Index" title="Index" rel="index">Index</a>]</p>
</div>


</body>
</html>