在这一篇文章中我先来介绍一下lua解析一个脚本文件时要用到的一些关键的数据结构，为将来的一系列代码分析打下一个良好的基础。在整个过程中，比较重要的几个源码文件分别是：llex.h，lparse.h、lobject.h和lopcode.h。
在llex.h中
1 typedef struct Token { 2 int token; 3 SemInfo seminfo; 4 } Token;
Token代表了一个词法单元，其中token表示词法类型如TK_NAME、TK_NUMBER等如果不是这些类型则存放则词素的字符表示，例如分析的代码会这么判断词素单元：
1 switch (ls->t.token) { 2 case '(': { 3 //... 4 } 5 case TK_NAME: { 6 //... 7 } 8 default: { 9 //... 10 }
在Token中SemInfo存放了一些语义相关的一些内容信息
1 typedef union { 2 lua_Number r; 3 TString *ts; 4 } SemInfo; /* semantics information */
其中当token是数字是内容存放在r中，其他情况存放在ts指向的TString中。
下面是最重要的一个数据结构之一
1 typedef struct LexState { 2 int current; /* current character (charint) */ 3 int linenumber; /* input line counter */ 4 int lastline; /* line of last token `consumed' */ 5 Token t; /* current token */ 6 Token lookahead; /* look ahead token */ 7 struct FuncState *fs; /* `FuncState' is private to the parser */ 8 struct lua_State *L; 9 ZIO *z; /* input stream */ 10 Mbuffer *buff; /* buffer for tokens */ 11 TString *source; /* current source name */ 12 char decpoint; /* locale decimal point */ 13 } LexState;
LexState不仅用于保存当前的词法分析状态信息，而且也保存了整个编译系统的全局状态。current指向了当前字符，t存放了当前的toekn，lookahead存放了向前看的token，由此我认为lua应该是ll(1)的~哈哈（不知道对不对）。fs指向了parser当前解析的函数的一些相关的信息，L指向了当前lua_State结构，z指向输入流，buff指向了token buffer，其他的看注释吧。
下面看看lparse.h文件中的重要结构：
1 typedef struct expdesc { 2 expkind k; 3 union { 4 struct { int info, aux; } s; 5 lua_Number nval; 6 } u; 7 int t; /* patch list of `exit when true' */ 8 int f; /* patch list of `exit when false' */ 9 } expdesc;
expdesc是存放了表达式的相关描述信息，k是表达式的种类，u在不同的表达式中有不同的含义。
1 typedef struct upvaldesc { 2 lu_byte k; 3 lu_byte info; 4 } upvaldesc;
upvaldesc是存放了upval的相关描述信息。
最后是本文件中最重要的结构：
1 typedef struct FuncState { 2 Proto *f; /* current function header */ 3 Table *h; /* table to find (and reuse) elements in `k' */ 4 struct FuncState *prev; /* enclosing function */ 5 struct LexState *ls; /* lexical state */ 6 struct lua_State *L; /* copy of the Lua state */ 7 struct BlockCnt *bl; /* chain of current blocks */ 8 int pc; /* next position to code (equivalent to `ncode') */ 9 int lasttarget; /* `pc' of last `jump target' */ 10 int jpc; /* list of pending jumps to `pc' */ 11 int freereg; /* first free register */ 12 int nk; /* number of elements in `k' */ 13 int np; /* number of elements in `p' */ 14 short nlocvars; /* number of elements in `locvars' */ 15 lu_byte nactvar; /* number of active local variables */ 16 upvaldesc upvalues[LUAI_MAXUPVALUES]; /* upvalues */ 17 unsigned short actvar[LUAI_MAXVARS]; /* declared-variable stack */ 18 } FuncState;
在编译过程中，使用FuncState结构体来保存一个函数编译的状态数据。其中，f指向了本函数的协议描述结构体，prev指向了其父函数的FuncState描述，因为在lua中可以在一个函数中定义另一个函数，因此当parse到一个函数的内部函数的定义时会new一个FuncState来描述内部函数，同时开始parse这个内部函数，将这个FuncState的prev指向其外部函数的FuncState，prev变量用来引用外围函数的FuncState，使当前所有没有分析完成的FuncState形成一个栈结构。bl指向当前parse的block，在一个函数中会有很多block代码，lua会将这些同属于同一个函数的block用链表串联起来。jpc是一个OP_JMP指令的链表，因为lua是一遍过的parse，在开始的时候有一些跳转指令不能决定其跳转位置，因此jpc将这些pending jmp指令串联起来，在以后能确定的时候回填，freereg为第一个空闲寄存器的下标，upvalues数组保存了当前函数的所有upvalue，nactvar是当前作用域的局部变量数。
在lparse.c中定义了BlockCnt
1 /* 2 ** nodes for block list (list of active blocks) 3 */ 4 typedef struct BlockCnt { 5 struct BlockCnt *previous; /* chain */ 6 int breaklist; /* list of jumps out of this loop */ 7 lu_byte nactvar; /* # active locals outside the breakable structure */ 8 lu_byte upval; /* true if some variable in the block is an upvalue */ 9 lu_byte isbreakable; /* true if `block' is a loop */ 10 } BlockCnt;
Lua使用BlockCnt来保存一个block的数据。与FuncState的分析方法类似，BlockCnt使用一个previous变量保存外围block的引用，形成一个栈结构。
下面介绍一些在lobject.h文件里面的数据结构
1 /* 2 ** Function Prototypes 3 */ 4 typedef struct Proto { 5 CommonHeader; 6 TValue *k; /* constants used by the function */ 7 Instruction *code; 8 struct Proto **p; /* functions defined inside the function */ 9 int *lineinfo; /* map from opcodes to source lines */ 10 struct LocVar *locvars; /* information about local variables */ 11 TString **upvalues; /* upvalue names */ 12 TString *source; 13 int sizeupvalues; 14 int sizek; /* size of `k' */ 15 int sizecode; 16 int sizelineinfo; 17 int sizep; /* size of `p' */ 18 int sizelocvars; 19 int linedefined; 20 int lastlinedefined; 21 GCObject *gclist; 22 lu_byte nups; /* number of upvalues */ 23 lu_byte numparams; 24 lu_byte is_vararg; 25 lu_byte maxstacksize; 26 } Proto;
结构体Proto是lua函数协议的描述，在lua解析脚本时首先会将main chunk代码包裹为一个函数，用main proto描述，接着将里面定义的内部函数一一用Proto结构体描述，将这些Proto的关系用树来组合起来，例如有lua源码文件如下
1 a = 1 2 function f1() 3 -- ... 4 end 5 function f2() 6 function f3() 7 -- ... 8 end 9 end
则parse完成后会有如图如下关系
在Proto结构体中，k指向一个const变量数组，存放则函数要用到的常量；code指向lua parse过程中生成的本函数的instruction集合；p就是指向本函数内部定义的函数的那些proto；locvars指向本函数局部变量数组；upvalues指向本函数upvalue变量数组；nups为upvalue的数量；numparams为函数参数的数量；is_vararg表示函数是否接收可变参数；maxstacksize为函数stack的max大小。
在编译期间lua使用Proto描述函数的，当lua vm开始运行vm时需要根据Proto生成相应的Closure来执行vm instructions。
1 typedef union Closure { 2 CClosure c; 3 LClosure l; 4 } Closure;
Closure要么代表了c函数，要么为lua函数，在这里我们只看lua函数的LClosure
1 #define ClosureHeader 2 CommonHeader; lu_byte isC; lu_byte nupvalues; GCObject *gclist; 3 struct Table *env 4 //... ... 5 typedef struct LClosure { 6 ClosureHeader; 7 struct Proto *p; 8 UpVal *upvals[1]; 9 } LClosure;
在LClousre中，p就是指向对应函数的Proto结构体啦，upvals顾名思义就是此closure的upvalue数组罗。在ClosureHeader宏中isC表示此closure是否是c函数，nupvalues为upvalue数目，env指向了此closue运行时的函数环境，在lua中可以用stefenv来改变当前函数的环境，就是改变env变量的指向啦。
最后，在文件lopcode.h中定义了lua vm的指令结构
下面是vm指令的一些定义与描述，我在相应vm指令的上方添加了一些注释
1 typedef enum { 2 /*---------------------------------------------------------------------- 3 name args description 4 ------------------------------------------------------------------------*/ 5 OP_MOVE,/* A B R(A) := R(B) */ 6 //Constants are usually numbers or strings. Each function has its own constant list, or pool. 7 OP_LOADK,/* A Bx R(A) := Kst(Bx) */ 8 OP_LOADBOOL,/* A B C R(A) := (Bool)B; if (C) pc++ */ 9 //The optimization rule is a simple one: If no other instructions have been generated, 10 //then a LOADNIL as the first instruction can be optimized away. 11 OP_LOADNIL,/* A B R(A) := ... := R(B) := nil */ 12 13 OP_GETUPVAL,/* A B R(A) := UpValue[B] */ 14 OP_GETGLOBAL,/* A Bx R(A) := Gbl[Kst(Bx)] */ 15 OP_GETTABLE,/* A B C R(A) := R(B)[RK(C)] */ 16 17 OP_SETGLOBAL,/* A Bx Gbl[Kst(Bx)] := R(A) */ 18 OP_SETUPVAL,/* A B UpValue[B] := R(A) */ 19 OP_SETTABLE,/* A B C R(A)[RK(B)] := RK(C) */ 20 21 OP_NEWTABLE,/* A B C R(A) := {} (size = B,C) */ 22 23 //This instruction is used for object-oriented programming. It is only generated for method calls that use the colon syntax. 24 //R(B) is the register holding the reference to the table with the method. 25 OP_SELF,/* A B C R(A+1) := R(B); R(A) := R(B)[RK(C)] */ 26 27 //The optimization rule is simple: If both terms of a subexpression are numbers, 28 //the subexpression will be evaluated at compile time. 29 OP_ADD,/* A B C R(A) := RK(B) + RK(C) */ 30 OP_SUB,/* A B C R(A) := RK(B) - RK(C) */ 31 OP_MUL,/* A B C R(A) := RK(B) * RK(C) */ 32 OP_DIV,/* A B C R(A) := RK(B) / RK(C) */ 33 OP_MOD,/* A B C R(A) := RK(B) % RK(C) */ 34 OP_POW,/* A B C R(A) := RK(B) ^ RK(C) */ 35 OP_UNM,/* A B R(A) := -R(B) */ 36 OP_NOT,/* A B R(A) := not R(B) */ 37 //Returns the length of the object in R(B) 38 OP_LEN,/* A B R(A) := length of R(B) */ 39 40 //Performs concatenation of two or more strings. 41 //The source registers must be consecutive, and C must always be greater than B. 42 OP_CONCAT,/* A B C R(A) := R(B).. ... ..R(C) */ 43 44 //if sBx is 0, the VM will proceed to the next instruction 45 OP_JMP,/* sBx pc+=sBx */ 46 47 /*If the boolean result is not A, then skip the next instruction. 48 Conversely, if the boolean result equals A, continue with the next instruction.*/ 49 OP_EQ,/* A B C if ((RK(B) == RK(C)) ~= A) then pc++ */ 50 OP_LT,/* A B C if ((RK(B) < RK(C)) ~= A) then pc++ */ 51 OP_LE,/* A B C if ((RK(B) <= RK(C)) ~= A) then pc++ */ 52 53 OP_TEST,/* A C if not (R(A) <=> C) then pc++ */ 54 //register R(B) is coerced into a boolean. 55 OP_TESTSET,/* A B C if (R(B) <=> C) then R(A) := R(B) else pc++ */ 56 57 //If B is 0, parameters range from R(A+1) to the top of the stack.If B is 1, the function has no parameters. 58 //If C is 1, no return results are saved. If C is 0, then multiple return results are saved, depending on the called function 59 //CALL always updates the top of stack value. 60 OP_CALL,/* A B C R(A), ... ,R(A+C-2) := R(A)(R(A+1), ... ,R(A+B-1)) */ 61 OP_TAILCALL,/* A B C return R(A)(R(A+1), ... ,R(A+B-1)) */ 62 //If B is 1, there are no return values. If B is 0, the set of values from R(A) to the top of the stack is returned. 63 OP_RETURN,/* A B return R(A), ... ,R(A+B-2) (see note) */ 64 65 //FORPREP initializes a numeric for loop, while FORLOOP performs an iteration of a numeric for loop. 66 OP_FORLOOP,/* A sBx R(A)+=R(A+2); 67 if R(A) <?= R(A+1) then { pc+=sBx; R(A+3)=R(A) }*/ 68 OP_FORPREP,/* A sBx R(A)-=R(A+2); pc+=sBx */ 69 70 //Performs an iteration of a generic for loop. 71 OP_TFORLOOP,/* A C R(A+3), ... ,R(A+2+C) := R(A)(R(A+1), R(A+2)); 72 if R(A+3) ~= nil then R(A+2)=R(A+3) else pc++ */ 73 //This instruction is used to initialize array elements in a table. 74 //If B is 0, the table is set with a variable number of array elements, from register R(A+1) up to the top of the stack. 75 //If C is 0, the next instruction is cast as an integer, and used as the C value. 76 OP_SETLIST,/* A B C R(A)[(C-1)*FPF+i] := R(A+i), 1 <= i <= B */ 77 78 /*If a local is used as an upvalue, then the local variable need to be placed somewhere, 79 other wise it will go out of scope and disappear when a lexicalblock enclosing the local variable ends. 80 CLOSE performs this operation for all affected local variables for do end blocks or loop blocks. 81 RETURN also does an implicit CLOSE when a function returns.*/ 82 OP_CLOSE,/* A close all variables in the stack up to (>=) R(A)*/ 83 /*Each upvalue corresponds to either a MOVE or a GETUPVAL pseudo-instruction. 84 Only the B field on either of these pseudo-instructions are significant.*/ 85 //MOVE pseudo-instructions corresponds to local variable R(B) in the current lexical block. 86 //GETUPVAL pseudo-instructions corresponds upvalue number B in the current lexical block. 87 OP_CLOSURE,/* A Bx R(A) := closure(KPROTO[Bx], R(A), ... ,R(A+n)) */ 88 89 //If B is 0, VARARG copies as many values as it can based on the number of parameters passed. 90 //If a fixed number of values is required, B is a value greater than 1. 91 OP_VARARG/* A B R(A), R(A+1), ..., R(A+B-1) = vararg */ 92 } OpCode;