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lua-notes.html
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<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1"/>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name="generator" content="Docutils 0.13.1: http://docutils.sourceforge.net/" />
<title>Lua 源码阅读笔记</title>
<link rel="stylesheet" href="style.css" type="text/css" />
<script type="text/javascript" src="script.js"></script>
</head>
<body>
<div class="document" id="lua">
<div id="top"></div>
<h1 class="title">Lua 源码阅读笔记</h1>
<style>
.document h2:before { content:""; }
.document h2:after { content:" :"; }
.document h2 { font-weight: bold; }
</style><div class="contents topic" id="id1">
<p class="topic-title first">目录</p>
<ul class="simple">
<li><a class="reference internal" href="#be-prepared" id="id5">Be Prepared</a></li>
<li><a class="reference internal" href="#lapi-c" id="id6">lapi.c</a><ul>
<li><a class="reference internal" href="#index2addr" id="id7">index2addr</a></li>
</ul>
</li>
<li><a class="reference internal" href="#lobject-h" id="id8">lobject.h</a><ul>
<li><a class="reference internal" href="#tvalue" id="id9">TValue</a></li>
<li><a class="reference internal" href="#value" id="id10">Value</a></li>
<li><a class="reference internal" href="#pseudo-index" id="id11">Pseudo Index</a></li>
<li><a class="reference internal" href="#commonheader" id="id12">CommonHeader</a></li>
</ul>
</li>
<li><a class="reference internal" href="#lstate-h" id="id13">lstate.h</a><ul>
<li><a class="reference internal" href="#gcobject" id="id14">GCObject</a></li>
<li><a class="reference internal" href="#callinfo" id="id15">CallInfo</a></li>
<li><a class="reference internal" href="#lua-state" id="id16">lua_State</a></li>
</ul>
</li>
<li><a class="reference internal" href="#lvm-c" id="id17">lvm.c</a><ul>
<li><a class="reference internal" href="#luav-execute" id="id18">luaV_execute</a></li>
</ul>
</li>
</ul>
</div>
<hr class="docutils" />
<p>某天在 reddit 上面看到 LuaJIT 作者推荐的 Lua源码阅读顺序 ：</p>
<blockquote>
<ol class="arabic simple">
<li>lmathlib.c, lstrlib.c: get familiar with the external C API. Don't bother with the pattern matcher though. Just the easy functions.</li>
<li>lapi.c: Check how the API is implemented internally. Only skim this to get a feeling for the code. Cross-reference to lua.h and luaconf.h as needed.</li>
<li>lobject.h: tagged values and object representation. skim through this first. you'll want to keep a window with this file open all the time.</li>
<li>lstate.h: state objects. ditto.</li>
<li>lopcodes.h: bytecode instruction format and opcode definitions. easy.</li>
<li>lvm.c: scroll down to luaV_execute, the main interpreter loop. see how all of the instructions are implemented. skip the details for now. reread later.</li>
<li>ldo.c: calls, stacks, exceptions, coroutines. tough read.</li>
<li>lstring.c: string interning. cute, huh?</li>
<li>ltable.c: hash tables and arrays. tricky code.</li>
<li>ltm.c: metamethod handling, reread all of lvm.c now.</li>
<li>You may want to reread lapi.c now.</li>
<li>ldebug.c: surprise waiting for you. abstract interpretation is used to find object names for tracebacks. does bytecode verification, too.</li>
<li>lparser.c, lcode.c: recursive descent parser, targetting a register-based VM. start from chunk() and work your way through. read the expression parser and the code generator parts last.</li>
<li>lgc.c: incremental garbage collector. take your time.</li>
<li>Read all the other files as you see references to them. Don't let your stack get too deep though.</li>
</ol>
</blockquote>
<p>感觉很有道理，所以……就按他说的来吧~</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p>唔，插一句…… GNU Global 真是神器！</p>
<p class="last">再插一句，其实他漏掉了第零步：Lua 文档</p>
</div>
<div class="section" id="be-prepared">
<h1><a class="toc-backref" href="#id5">Be Prepared</a></h1>
<ul class="simple">
<li>去看看 <a class="reference external" href="http://www.lua.org/manual/5.2/manual.html">Lua Manual</a></li>
<li>去 <a class="reference external" href="http://lua-users.org/wiki/LuaSource">Lua Wiki</a> 看看 Lua 代码的组织方式和代码风格</li>
<li>打开 <a class="reference external" href="http://www.lua.org/source/5.2/">Lua Source</a> 对着看</li>
</ul>
<p>Lua 代码风格：</p>
<pre class="literal-block">
luaA_ - lapi.c
luaB_ - lbaselib.c
luaC_ - lgc.c
luaD_ - ldo.c
luaE_ - lstate.c
luaF_ - lfunc.c
luaG_ - ldebug.c
luaH_ - ltable.c
luaI_ - lauxlib.c
luaK_ - lcode.c
luaL_ - lauxlib.c/h, linit.c (public functions)
luaM_ - lmem.c
luaO_ - lobject.c
luaP_ - lopcodes.c
luaS_ - lstring.c
luaT_ - ltm.c
luaU_ - lundump.c
luaV_ - lvm.c
luaX_ - llex.c
luaY_ - lparser.c
luaZ_ - lzio.c
lua_ - lapi.c/h + luaconf.h, debug.c
luai_ - luaconf.h
luaopen_ - luaconf.h + libraries (lbaselib.c, ldblib.c, liolib.c, lmathlib.c,
loadlib.c, loslib.c, lstrlib.c, ltablib.c)
</pre>
</div>
<div class="section" id="lapi-c">
<h1><a class="toc-backref" href="#id6">lapi.c</a></h1>
<p>在 <cite>lapi.c</cite> 中，最重要的函数可以说是 <tt class="docutils literal">index2addr</tt> 了吧：</p>
<div class="section" id="index2addr">
<h2><a class="toc-backref" href="#id7">index2addr</a></h2>
<pre class="code c literal-block">
<span class="k">static</span> <span class="n">TValue</span> <span class="o">*</span><span class="nf">index2addr</span> <span class="p">(</span><span class="n">lua_State</span> <span class="o">*</span><span class="n">L</span><span class="p">,</span> <span class="kt">int</span> <span class="n">idx</span><span class="p">)</span> <span class="p">{</span>
<span class="n">CallInfo</span> <span class="o">*</span><span class="n">ci</span> <span class="o">=</span> <span class="n">L</span><span class="o">-></span><span class="n">ci</span><span class="p">;</span>
<span class="k">if</span> <span class="p">(</span><span class="n">idx</span> <span class="o">></span> <span class="mi">0</span><span class="p">)</span> <span class="p">{</span>
<span class="n">TValue</span> <span class="o">*</span><span class="n">o</span> <span class="o">=</span> <span class="n">ci</span><span class="o">-></span><span class="n">func</span> <span class="o">+</span> <span class="n">idx</span><span class="p">;</span>
<span class="n">api_check</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">idx</span> <span class="o"><=</span> <span class="n">ci</span><span class="o">-></span><span class="n">top</span> <span class="o">-</span> <span class="p">(</span><span class="n">ci</span><span class="o">-></span><span class="n">func</span> <span class="o">+</span> <span class="mi">1</span><span class="p">),</span> <span class="s">"unacceptable index"</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">o</span> <span class="o">>=</span> <span class="n">L</span><span class="o">-></span><span class="n">top</span><span class="p">)</span> <span class="k">return</span> <span class="n">NONVALIDVALUE</span><span class="p">;</span>
<span class="k">else</span> <span class="k">return</span> <span class="n">o</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">idx</span> <span class="o">></span> <span class="n">LUA_REGISTRYINDEX</span><span class="p">)</span> <span class="p">{</span>
<span class="n">api_check</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">idx</span> <span class="o">!=</span> <span class="mi">0</span> <span class="o">&&</span> <span class="o">-</span><span class="n">idx</span> <span class="o"><=</span> <span class="n">L</span><span class="o">-></span><span class="n">top</span> <span class="o">-</span> <span class="p">(</span><span class="n">ci</span><span class="o">-></span><span class="n">func</span> <span class="o">+</span> <span class="mi">1</span><span class="p">),</span> <span class="s">"invalid index"</span><span class="p">);</span>
<span class="k">return</span> <span class="n">L</span><span class="o">-></span><span class="n">top</span> <span class="o">+</span> <span class="n">idx</span><span class="p">;</span>
<span class="p">}</span>
<span class="k">else</span> <span class="k">if</span> <span class="p">(</span><span class="n">idx</span> <span class="o">==</span> <span class="n">LUA_REGISTRYINDEX</span><span class="p">)</span>
<span class="k">return</span> <span class="o">&</span><span class="n">G</span><span class="p">(</span><span class="n">L</span><span class="p">)</span><span class="o">-></span><span class="n">l_registry</span><span class="p">;</span>
<span class="k">else</span> <span class="p">{</span> <span class="cm">/* upvalues */</span>
<span class="n">idx</span> <span class="o">=</span> <span class="n">LUA_REGISTRYINDEX</span> <span class="o">-</span> <span class="n">idx</span><span class="p">;</span>
<span class="n">api_check</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">idx</span> <span class="o"><=</span> <span class="n">MAXUPVAL</span> <span class="o">+</span> <span class="mi">1</span><span class="p">,</span> <span class="s">"upvalue index too large"</span><span class="p">);</span>
<span class="k">if</span> <span class="p">(</span><span class="n">ttislcf</span><span class="p">(</span><span class="n">ci</span><span class="o">-></span><span class="n">func</span><span class="p">))</span> <span class="cm">/* light C function? */</span>
<span class="k">return</span> <span class="n">NONVALIDVALUE</span><span class="p">;</span> <span class="cm">/* it has no upvalues */</span>
<span class="k">else</span> <span class="p">{</span>
<span class="n">CClosure</span> <span class="o">*</span><span class="n">func</span> <span class="o">=</span> <span class="n">clCvalue</span><span class="p">(</span><span class="n">ci</span><span class="o">-></span><span class="n">func</span><span class="p">);</span>
<span class="k">return</span> <span class="p">(</span><span class="n">idx</span> <span class="o"><=</span> <span class="n">func</span><span class="o">-></span><span class="n">nupvalues</span><span class="p">)</span> <span class="o">?</span> <span class="o">&</span><span class="n">func</span><span class="o">-></span><span class="n">upvalue</span><span class="p">[</span><span class="n">idx</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">:</span> <span class="n">NONVALIDVALUE</span><span class="p">;</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
<p>几乎所有其他的函数都是建立在它的功能之上的 —— 回忆 Lua 文档，
很多的 Lua API 函数都会接受一个 index 参数，用来指定参数在栈上的位置，比如 <tt class="docutils literal">lua_settop</tt>, <tt class="docutils literal">lua_remove</tt>, <tt class="docutils literal">lua_insert</tt>,
<tt class="docutils literal">lua_replace</tt> 等等，而这个 <a class="reference internal" href="#index2addr">index2addr</a> 函数的作用就是通过给定的 index 参数取出对应的 <a class="reference internal" href="#tvalue">TValue</a> 类型的对象指针</p>
<p>关于 Registry 的应用可以回忆 <a class="reference external" href="http://www.lua.org/manual/5.2/manual.html#4.5">Lua 文档上对于 Registry 的介绍</a> 。</p>
<p>而结合 <a class="reference internal" href="#pseudo-index">Pseudo Index</a> 可以看出该函数的逻辑如下：</p>
<table border="1" class="docutils">
<colgroup>
<col width="46%" />
<col width="54%" />
</colgroup>
<tbody valign="top">
<tr><td>当 index > 0 时</td>
<td>在当前 function 的栈空间找对应的 TValue</td>
</tr>
<tr><td>当 LUA_REGISTRYINDEX < index <= 0 时</td>
<td>在当前 function 的栈空间逆向找对应的 TValue</td>
</tr>
<tr><td>当 index == LUA_REGISTRYINDEX 时</td>
<td>返回 registry</td>
</tr>
<tr><td>否则( index < LUA_REGISTRYINDEX 时 )</td>
<td>查找 upvalue</td>
</tr>
</tbody>
</table>
</div>
</div>
<div class="section" id="lobject-h">
<h1><a class="toc-backref" href="#id8">lobject.h</a></h1>
<div class="section" id="tvalue">
<h2><a class="toc-backref" href="#id9">TValue</a></h2>
<pre class="code c literal-block">
<span class="k">typedef</span> <span class="k">struct</span> <span class="n">lua_TValue</span> <span class="n">TValue</span><span class="p">;</span>
<span class="k">struct</span> <span class="n">lua_TValue</span> <span class="p">{</span>
<span class="n">TValuefields</span><span class="p">;</span>
<span class="p">};</span>
<span class="cp">#define TValuefields Value value_; int tt_</span>
</pre>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">#define LUA_NANTRICK 之后， TValuefields 会有不同的定义，不过基本原理不便，此处暂且假定
<strong>没有使用 LUA_NANTRICK</strong></p>
</div>
<p><cite>value_</cite> 项用于保存数据， <cite>tt_</cite> 项用于保存数据类型；
可选的数据类型有：</p>
<pre class="code c literal-block" id="id3">
<span class="cp">#define LUA_TNONE (-1)
</span>
<span class="cp">#define LUA_TNIL 0
#define LUA_TBOOLEAN 1
#define LUA_TLIGHTUSERDATA 2
#define LUA_TNUMBER 3
#define LUA_TSTRING 4
#define LUA_TTABLE 5
#define LUA_TFUNCTION 6
#define LUA_TUSERDATA 7
#define LUA_TTHREAD 8</span>
</pre>
<p>BTW 其中 function 类型又有三种区分：</p>
<ul class="simple">
<li>lua function</li>
<li>light C function</li>
<li>C function</li>
</ul>
<p>其中 light C function 与 C function 的区别在于前者只是一个 C 函数指针，
而后者可以有自己的 upvalue，即可以构成一个 closure。</p>
<p>string 类型有两种区分：</p>
<ul class="simple">
<li>short string</li>
<li>long string</li>
</ul>
<p>这两者的区别则在于前者会计算 hash 值，保证相同的短字符串全局唯一；
而为了避免 <a class="reference external" href="http://lua-users.org/wiki/HashDos">hash dos</a> ，长字符串并不计算 hash 值</p>
<pre class="code c literal-block">
<span class="cm">/* Variant tags for functions */</span>
<span class="cp">#define LUA_TLCL (LUA_TFUNCTION | (0 << 4)) </span><span class="cm">/* Lua closure */</span><span class="cp">
#define LUA_TLCF (LUA_TFUNCTION | (1 << 4)) </span><span class="cm">/* light C function */</span><span class="cp">
#define LUA_TCCL (LUA_TFUNCTION | (2 << 4)) </span><span class="cm">/* C closure */</span><span class="cp">
</span>
<span class="cm">/*
** LUA_TSTRING variants */</span>
<span class="cp">#define LUA_TSHRSTR (LUA_TSTRING | (0 << 4)) </span><span class="cm">/* short strings */</span><span class="cp">
#define LUA_TLNGSTR (LUA_TSTRING | (1 << 4)) </span><span class="cm">/* long strings */</span>
</pre>
</div>
<div class="section" id="value">
<h2><a class="toc-backref" href="#id10">Value</a></h2>
<pre class="code c literal-block">
<span class="k">union</span> <span class="n">Value</span> <span class="p">{</span>
<span class="n">GCObject</span> <span class="o">*</span><span class="n">gc</span><span class="p">;</span> <span class="cm">/* collectable objects */</span>
<span class="kt">void</span> <span class="o">*</span><span class="n">p</span><span class="p">;</span> <span class="cm">/* light userdata */</span>
<span class="kt">int</span> <span class="n">b</span><span class="p">;</span> <span class="cm">/* booleans */</span>
<span class="n">lua_CFunction</span> <span class="n">f</span><span class="p">;</span> <span class="cm">/* light C functions */</span>
<span class="n">numfield</span> <span class="cm">/* numbers */</span>
<span class="p">};</span>
<span class="k">typedef</span> <span class="k">union</span> <span class="n">GCObject</span> <span class="n">GCObject</span><span class="p">;</span>
</pre>
<p>可以看出除了按值引用的数据（ light userdata, boolean, light C function, number ），
其他（ string, table, function, userdata, thread ）都是以 <a class="reference internal" href="#gcobject">GCObject</a> 指针形式保存，
以便用于垃圾回收</p>
</div>
<div class="section" id="pseudo-index">
<h2><a class="toc-backref" href="#id11">Pseudo Index</a></h2>
<pre class="code c literal-block">
<span class="cp">#define LUAI_FIRSTPSEUDOIDX (-LUAI_MAXSTACK - 1000)
</span>
<span class="cp">#define LUA_REGISTRYINDEX LUAI_FIRSTPSEUDOIDX
#define lua_upvalueindex(i) (LUA_REGISTRYINDEX - (i))</span>
</pre>
</div>
<div class="section" id="commonheader">
<h2><a class="toc-backref" href="#id12">CommonHeader</a></h2>
<pre class="code c literal-block">
<span class="cm">/*
** Common Header for all collectable objects (in macro form, to be
** included in other objects)
*/</span>
<span class="cp">#define CommonHeader GCObject *next; lu_byte tt; lu_byte marked</span>
</pre>
<p>CommonHeader 是 Lua 用于垃圾回收的结构，其中 <a class="reference internal" href="#gcobject">GCObject</a> * next 指向下一个可回收对象，
构成了一个单向链表，tt <a class="reference internal" href="#tvalue">依旧是</a> 用于保存数据类型，而 marked 则是用于标记垃圾回收的状态</p>
</div>
</div>
<div class="section" id="lstate-h">
<h1><a class="toc-backref" href="#id13">lstate.h</a></h1>
<div class="section" id="gcobject">
<h2><a class="toc-backref" href="#id14">GCObject</a></h2>
<pre class="code c literal-block">
<span class="k">union</span> <span class="n">GCObject</span> <span class="p">{</span>
<span class="n">GCheader</span> <span class="n">gch</span><span class="p">;</span> <span class="cm">/* common header */</span>
<span class="k">union</span> <span class="n">TString</span> <span class="n">ts</span><span class="p">;</span>
<span class="k">union</span> <span class="n">Udata</span> <span class="n">u</span><span class="p">;</span>
<span class="k">union</span> <span class="n">Closure</span> <span class="n">cl</span><span class="p">;</span>
<span class="k">struct</span> <span class="n">Table</span> <span class="n">h</span><span class="p">;</span>
<span class="k">struct</span> <span class="n">Proto</span> <span class="n">p</span><span class="p">;</span>
<span class="k">struct</span> <span class="n">UpVal</span> <span class="n">uv</span><span class="p">;</span>
<span class="k">struct</span> <span class="n">lua_State</span> <span class="n">th</span><span class="p">;</span> <span class="cm">/* thread */</span>
<span class="p">};</span>
</pre>
</div>
<div class="section" id="callinfo">
<h2><a class="toc-backref" href="#id15">CallInfo</a></h2>
<pre class="code c literal-block">
<span class="cm">/*
** information about a call
*/</span>
<span class="k">typedef</span> <span class="k">struct</span> <span class="n">CallInfo</span> <span class="p">{</span>
<span class="n">StkId</span> <span class="n">func</span><span class="p">;</span> <span class="cm">/* function index in the stack */</span>
<span class="n">StkId</span> <span class="n">top</span><span class="p">;</span> <span class="cm">/* top for this function */</span>
<span class="k">struct</span> <span class="n">CallInfo</span> <span class="o">*</span><span class="n">previous</span><span class="p">,</span> <span class="o">*</span><span class="n">next</span><span class="p">;</span> <span class="cm">/* dynamic call link */</span>
<span class="kt">short</span> <span class="n">nresults</span><span class="p">;</span> <span class="cm">/* expected number of results from this function */</span>
<span class="n">lu_byte</span> <span class="n">callstatus</span><span class="p">;</span>
<span class="kt">ptrdiff_t</span> <span class="n">extra</span><span class="p">;</span>
<span class="k">union</span> <span class="p">{</span>
<span class="k">struct</span> <span class="p">{</span> <span class="cm">/* only for Lua functions */</span>
<span class="n">StkId</span> <span class="n">base</span><span class="p">;</span> <span class="cm">/* base for this function */</span>
<span class="k">const</span> <span class="n">Instruction</span> <span class="o">*</span><span class="n">savedpc</span><span class="p">;</span>
<span class="p">}</span> <span class="n">l</span><span class="p">;</span>
<span class="k">struct</span> <span class="p">{</span> <span class="cm">/* only for C functions */</span>
<span class="kt">int</span> <span class="n">ctx</span><span class="p">;</span> <span class="cm">/* context info. in case of yields */</span>
<span class="n">lua_CFunction</span> <span class="n">k</span><span class="p">;</span> <span class="cm">/* continuation in case of yields */</span>
<span class="kt">ptrdiff_t</span> <span class="n">old_errfunc</span><span class="p">;</span>
<span class="n">lu_byte</span> <span class="n">old_allowhook</span><span class="p">;</span>
<span class="n">lu_byte</span> <span class="n">status</span><span class="p">;</span>
<span class="p">}</span> <span class="n">c</span><span class="p">;</span>
<span class="p">}</span> <span class="n">u</span><span class="p">;</span>
<span class="p">}</span> <span class="n">CallInfo</span><span class="p">;</span>
<span class="cm">/*
** Bits in CallInfo status
*/</span>
<span class="cp">#define CIST_LUA (1<<0) </span><span class="cm">/* call is running a Lua function */</span><span class="cp">
#define CIST_HOOKED (1<<1) </span><span class="cm">/* call is running a debug hook */</span><span class="cp">
#define CIST_REENTRY (1<<2) </span><span class="cm">/* call is running on same invocation of
luaV_execute of previous call */</span><span class="cp">
#define CIST_YIELDED (1<<3) </span><span class="cm">/* call reentered after suspension */</span><span class="cp">
#define CIST_YPCALL (1<<4) </span><span class="cm">/* call is a yieldable protected call */</span><span class="cp">
#define CIST_STAT (1<<5) </span><span class="cm">/* call has an error status (pcall) */</span><span class="cp">
#define CIST_TAIL (1<<6) </span><span class="cm">/* call was tail called */</span><span class="cp">
#define CIST_HOOKYIELD (1<<7) </span><span class="cm">/* last hook called yielded */</span>
</pre>
</div>
<div class="section" id="lua-state">
<h2><a class="toc-backref" href="#id16">lua_State</a></h2>
<p>这是每个 Lua 函数都会接受的表示当前状态的结构，最主要的成员包括运行栈 stack,
栈用于表示函数调用、传递参数及返回值</p>
<pre class="code c literal-block">
<span class="cm">/*
** `per thread' state
*/</span>
<span class="k">struct</span> <span class="n">lua_State</span> <span class="p">{</span>
<span class="n">CommonHeader</span><span class="p">;</span>
<span class="n">lu_byte</span> <span class="n">status</span><span class="p">;</span>
<span class="n">StkId</span> <span class="n">top</span><span class="p">;</span> <span class="cm">/* first free slot in the stack */</span>
<span class="n">global_State</span> <span class="o">*</span><span class="n">l_G</span><span class="p">;</span>
<span class="n">CallInfo</span> <span class="o">*</span><span class="n">ci</span><span class="p">;</span> <span class="cm">/* call info for current function */</span>
<span class="k">const</span> <span class="n">Instruction</span> <span class="o">*</span><span class="n">oldpc</span><span class="p">;</span> <span class="cm">/* last pc traced */</span>
<span class="n">StkId</span> <span class="n">stack_last</span><span class="p">;</span> <span class="cm">/* last free slot in the stack */</span>
<span class="n">StkId</span> <span class="n">stack</span><span class="p">;</span> <span class="cm">/* stack base */</span>
<span class="kt">int</span> <span class="n">stacksize</span><span class="p">;</span>
<span class="kt">unsigned</span> <span class="kt">short</span> <span class="n">nny</span><span class="p">;</span> <span class="cm">/* number of non-yieldable calls in stack */</span>
<span class="kt">unsigned</span> <span class="kt">short</span> <span class="n">nCcalls</span><span class="p">;</span> <span class="cm">/* number of nested C calls */</span>
<span class="n">lu_byte</span> <span class="n">hookmask</span><span class="p">;</span>
<span class="n">lu_byte</span> <span class="n">allowhook</span><span class="p">;</span>
<span class="kt">int</span> <span class="n">basehookcount</span><span class="p">;</span>
<span class="kt">int</span> <span class="n">hookcount</span><span class="p">;</span>
<span class="n">lua_Hook</span> <span class="n">hook</span><span class="p">;</span>
<span class="n">GCObject</span> <span class="o">*</span><span class="n">openupval</span><span class="p">;</span> <span class="cm">/* list of open upvalues in this stack */</span>
<span class="n">GCObject</span> <span class="o">*</span><span class="n">gclist</span><span class="p">;</span>
<span class="k">struct</span> <span class="n">lua_longjmp</span> <span class="o">*</span><span class="n">errorJmp</span><span class="p">;</span> <span class="cm">/* current error recover point */</span>
<span class="kt">ptrdiff_t</span> <span class="n">errfunc</span><span class="p">;</span> <span class="cm">/* current error handling function (stack index) */</span>
<span class="n">CallInfo</span> <span class="n">base_ci</span><span class="p">;</span> <span class="cm">/* CallInfo for first level (C calling Lua) */</span>
<span class="p">};</span>
</pre>
</div>
</div>
<div class="section" id="lvm-c">
<h1><a class="toc-backref" href="#id17">lvm.c</a></h1>
<p>首先 <tt class="docutils literal">Instruction</tt> 的定义是 <tt class="docutils literal">uint32</tt></p>
<p>留意一下 lvm.h 这一段很重要的注释</p>
<pre class="code c literal-block">
<span class="cm">/*===========================================================================
We assume that instructions are unsigned numbers.
All instructions have an opcode in the first 6 bits.
Instructions can have the following fields:
`A' : 8 bits
`B' : 9 bits
`C' : 9 bits
'Ax' : 26 bits ('A', 'B', and 'C' together)
`Bx' : 18 bits (`B' and `C' together)
`sBx' : signed Bx
A signed argument is represented in excess K; that is, the number
value is the unsigned value minus K. K is exactly the maximum value
for that argument (so that -max is represented by 0, and +max is
represented by 2*max), which is half the maximum for the corresponding
unsigned argument.
===========================================================================*/</span>
</pre>
<p>我们可以发现体积最大的操作数 <tt class="docutils literal">Ax</tt> 加上 6bit 指令正好有 32 位 —— 不难猜出虚拟机的指令组织方式</p>
<div class="section" id="luav-execute">
<h2><a class="toc-backref" href="#id18">luaV_execute</a></h2>
<p>虚拟机本体</p>
<p>随便取一个指令的解析来看看：</p>
<pre class="code c literal-block">
<span class="n">vmcase</span><span class="p">(</span><span class="n">OP_MOVE</span><span class="p">,</span>
<span class="n">setobjs2s</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="n">ra</span><span class="p">,</span> <span class="n">RB</span><span class="p">(</span><span class="n">i</span><span class="p">));</span>
<span class="p">)</span>
</pre>
<p><tt class="docutils literal">ra</tt> 是用 <tt class="docutils literal">RA(</tt> <a class="reference internal" href="#callinfo">CallInfo</a>.u.l.savedpc <tt class="docutils literal">)</tt> 取出的，而 <tt class="docutils literal">RA</tt> 所做的事情是取出指令（此处即 <tt class="docutils literal">savedpc</tt> ）中的第 7-14 位的数值，然后加上 base 地址，获得一个 TValue 的指针</p>
<p><tt class="docutils literal">RB</tt> 做的也是类似的事情，所以这句话就是说遇到 <tt class="docutils literal">OP_MOVE</tt> 指令的时候对紧接在后面的 <tt class="docutils literal">A</tt>, <tt class="docutils literal">B</tt> 两个操作数执行 <tt class="docutils literal">setobjs2s</tt> 操作</p>
<blockquote>
PS. <tt class="docutils literal">newframe</tt> 标签看上去真是个万般无奈的解啊</blockquote>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">to be continued ...</p>
</div>
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