152 lines
6.3 KiB
HTML
152 lines
6.3 KiB
HTML
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>Symbol-table - Untitled</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="Untitled">
|
||
|
|
<meta name="generator" content="makeinfo 4.7">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="up" href="mmo.html#mmo" title="mmo">
|
||
|
|
<link rel="prev" href="File-layout.html#File-layout" title="File layout">
|
||
|
|
<link rel="next" href="mmo-section-mapping.html#mmo-section-mapping" title="mmo section mapping">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
This file documents the BFD library.
|
||
|
|
|
||
|
|
Copyright (C) 1991, 2000, 2001, 2003, 2006, 2007 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 1.1 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.-->
|
||
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
||
|
|
<style type="text/css"><!--
|
||
|
|
pre.display { font-family:inherit }
|
||
|
|
pre.format { font-family:inherit }
|
||
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallexample { font-size:smaller }
|
||
|
|
pre.smalllisp { font-size:smaller }
|
||
|
|
span.sc { font-variant:small-caps }
|
||
|
|
span.roman { font-family: serif; font-weight: normal; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div class="node">
|
||
|
|
<p>
|
||
|
|
<a name="Symbol_002dtable"></a>Next: <a rel="next" accesskey="n" href="mmo-section-mapping.html#mmo-section-mapping">mmo section mapping</a>,
|
||
|
|
Previous: <a rel="previous" accesskey="p" href="File-layout.html#File-layout">File layout</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="mmo.html#mmo">mmo</a>
|
||
|
|
<hr><br>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h4 class="subsection">3.5.2 Symbol table format</h4>
|
||
|
|
|
||
|
|
<p>From mmixal.w (or really, the generated mmixal.tex) in
|
||
|
|
<a href="http://www-cs-faculty.stanford.edu/~knuth/programs/mmix.tar.gz">http://www-cs-faculty.stanford.edu/~knuth/programs/mmix.tar.gz</a>):
|
||
|
|
“Symbols are stored and retrieved by means of a <span class="samp">ternary
|
||
|
|
search trie</span>, following ideas of Bentley and Sedgewick. (See
|
||
|
|
ACM–SIAM Symp. on Discrete Algorithms <span class="samp">8</span> (1997), 360–369;
|
||
|
|
R.Sedgewick, <span class="samp">Algorithms in C</span> (Reading, Mass.
|
||
|
|
Addison–Wesley, 1998), <span class="samp">15.4</span>.) 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.”
|
||
|
|
|
||
|
|
<p>So it'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>First, there'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:
|
||
|
|
|
||
|
|
<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 & 0xf).
|
||
|
|
|
||
|
|
(MMO3_REGQUAL_BITS)
|
||
|
|
j == 0xf: A register variable. The following
|
||
|
|
byte tells which register.
|
||
|
|
j <= 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 > 8: As with j <= 8, but add (0x20 << 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>
|
||
|
|
<p>Let's look again at the <code>lop_stab</code> for the trivial file
|
||
|
|
(see <a href="File-layout.html#File-layout">File layout</a>).
|
||
|
|
|
||
|
|
<pre class="example"> 0x980b0000 - lop_stab for ":Main" = 0, serial 1.
|
||
|
|
0x203a4040
|
||
|
|
0x10404020
|
||
|
|
0x4d206120
|
||
|
|
0x69016e00
|
||
|
|
0x81000000
|
||
|
|
</pre>
|
||
|
|
<p>This forms the trivial trie (note that the path between “:” and
|
||
|
|
“M” is redundant):
|
||
|
|
|
||
|
|
<pre class="example"> 203a ":"
|
||
|
|
40 /
|
||
|
|
40 /
|
||
|
|
10 \
|
||
|
|
40 /
|
||
|
|
40 /
|
||
|
|
204d "M"
|
||
|
|
2061 "a"
|
||
|
|
2069 "i"
|
||
|
|
016e "n" 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>
|
||
|
|
</body></html>
|
||
|
|
|