PERL原码分析2

﹏ヽ暗。殇╰゛Y 2022-08-27 02:25 44阅读 0赞

继续：

int Perl\_yyparse (pTHX\_ int gramtype)\{

\----从这两句话，我们看出，有两个变量用于parser，也就是说，是一种多层语言。

这种技术，是很常见的。比如，解析一门语言时，进入了另一种状态，比如进入了注释。

往前，我们找到最重要的一句话：

parser->yychar = yylex();

，所有的编译器都是这样的，lex是yacc的一个工具。所以，自然要从yacc中调用lex.

简单来说，编译器，是一种流式的解析器，它一次读入流，完成一个任务。

虽然，有的编译器，如C语言，理论上，是多遍完成解析的，因为有预编译。

但，对于每一次来说，也就是每一种输入来说，只需要解析一次。

这也是编译器的精妙之处。

lex的任务，是一个字符，一个字符地读入，然后驱动内部的状态机。当状态机被激发，则会发给yacc一个token.

前面我解释过了，perl解析器，没有专门编写一个lex文件，而是直接手工编写了一个token. 只是原理，也lex没有差别。

============

歇一会，

的第504行找到：

/\* A bare statement, lacking label and other aspects of state op \*/  
barestmt: PLUGSTMT  
\{ $$ = $1; \}  
| PEG  
\{  
$$ = newOP(OP\_NULL,0);  
TOKEN\_GETMAD($1,$$,'p');  
\}

。。。

**| ';'  
\{  
PL\_parser->expect = XSTATE;  
$$ = IF\_MAD(newOP(OP\_NULL, 0), (OP\*)NULL);  
TOKEN\_GETMAD($1,$$,';');  
PL\_parser->copline = NOLINE;  
\}  
;**

========================================

现在，停掉重头再来。

因为关键的东西还都没有找到。

重新写个脚本，最简单的：

前面，打两个回车，然后定义个变量，就可以了。

编译器都是这样写的，从一个个简单的语句解析开始。

然后，在token.c中，找到一句话：

void  
Perl\_lex\_start(pTHX\_ SV \*line, PerlIO \*rsfp, U32 flags)  
\{

。。。

**parser->linestart = SvPVX(parser->linestr);**

**parser->linestr**，是在哪里初始化的呢？

\-----------

SvPVX，是从yacc的当前yyval中，得到想要的东西。因为yyval是一个union，所以，要根据需要，得到那个具体的值。

define SvPVX(sv) ((sv)->sv\_u.svu\_pv)

char \*linestart; /\* beginning of most recently read line \*/

\-------------------------

重来。

![20140429104935593][]

真是难搞。

找到了第一行处。

我一定是错过了许多东西。而且大部分地方，也没看懂。

原来是想拿来直接用perl解析器。

然后加个自定义的东西。

现在来看，太难了。

我再想想其它的办法。

就算是一个记录吧。

找到第一个identify是在这里：

![20140429110320531][]

现在，才明白，原来lex和yacc的解析器，语法与perl很象。

找到了赋值语句：

/\* Binary operators between terms \*/  
termbinop: term ASSIGNOP term /\* $x = $y \*/  
\{ $$ = newASSIGNOP(OPf\_STACKED, $1, IVAL($2), $3);  
TOKEN\_GETMAD($2,$$,'o');  
\}

在核心的op.c中：

/*
    =for apidoc Am|OP *|newASSIGNOP|I32 flags|OP *left|I32 optype|OP *right
    
    Constructs, checks, and returns an assignment op.  I<left> and I<right>
    supply the parameters of the assignment; they are consumed by this
    function and become part of the constructed op tree.
    
    If I<optype> is C<OP_ANDASSIGN>, C<OP_ORASSIGN>, or C<OP_DORASSIGN>, then
    a suitable conditional optree is constructed.  If I<optype> is the opcode
    of a binary operator, such as C<OP_BIT_OR>, then an op is constructed that
    performs the binary operation and assigns the result to the left argument.
    Either way, if I<optype> is non-zero then I<flags> has no effect.
    
    If I<optype> is zero, then a plain scalar or list assignment is
    constructed.  Which type of assignment it is is automatically determined.
    I<flags> gives the eight bits of C<op_flags>, except that C<OPf_KIDS>
    will be set automatically, and, shifted up eight bits, the eight bits
    of C<op_private>, except that the bit with value 1 or 2 is automatically
    set as required.
    
    =cut
    */
    
    OP *
    Perl_newASSIGNOP(pTHX_ I32 flags, OP *left, I32 optype, OP *right)
    {
        dVAR;
        OP *o;
    
        if (optype) {
    	if (optype == OP_ANDASSIGN || optype == OP_ORASSIGN || optype == OP_DORASSIGN) {
    	    return newLOGOP(optype, 0,
    		op_lvalue(scalar(left), optype),
    		newUNOP(OP_SASSIGN, 0, scalar(right)));
    	}
    	else {
    	    return newBINOP(optype, OPf_STACKED,
    		op_lvalue(scalar(left), optype), scalar(right));
    	}
        }
    
        if (is_list_assignment(left)) {
    	static const char no_list_state[] = "Initialization of state variables"
    	    " in list context currently forbidden";
    	OP *curop;
    	bool maybe_common_vars = TRUE;
    
    	PL_modcount = 0;
    	left = op_lvalue(left, OP_AASSIGN);
    	curop = list(force_list(left));
    	o = newBINOP(OP_AASSIGN, flags, list(force_list(right)), curop);
    	o->op_private = (U8)(0 | (flags >> 8));
    
    	if ((left->op_type == OP_LIST
    	     || (left->op_type == OP_NULL && left->op_targ == OP_LIST)))
    	{
    	    OP* lop = ((LISTOP*)left)->op_first;
    	    maybe_common_vars = FALSE;
    	    while (lop) {
    		if (lop->op_type == OP_PADSV ||
    		    lop->op_type == OP_PADAV ||
    		    lop->op_type == OP_PADHV ||
    		    lop->op_type == OP_PADANY) {
    		    if (!(lop->op_private & OPpLVAL_INTRO))
    			maybe_common_vars = TRUE;
    
    		    if (lop->op_private & OPpPAD_STATE) {
    			if (left->op_private & OPpLVAL_INTRO) {
    			    /* Each variable in state($a, $b, $c) = ... */
    			}
    			else {
    			    /* Each state variable in
    			       (state $a, my $b, our $c, $d, undef) = ... */
    			}
    			yyerror(no_list_state);
    		    } else {
    			/* Each my variable in
    			   (state $a, my $b, our $c, $d, undef) = ... */
    		    }
    		} else if (lop->op_type == OP_UNDEF ||
    			   lop->op_type == OP_PUSHMARK) {
    		    /* undef may be interesting in
    		       (state $a, undef, state $c) */
    		} else {
    		    /* Other ops in the list. */
    		    maybe_common_vars = TRUE;
    		}
    		lop = lop->op_sibling;
    	    }
    	}
    	else if ((left->op_private & OPpLVAL_INTRO)
    		&& (   left->op_type == OP_PADSV
    		    || left->op_type == OP_PADAV
    		    || left->op_type == OP_PADHV
    		    || left->op_type == OP_PADANY))
    	{
    	    if (left->op_type == OP_PADSV) maybe_common_vars = FALSE;
    	    if (left->op_private & OPpPAD_STATE) {
    		/* All single variable list context state assignments, hence
    		   state ($a) = ...
    		   (state $a) = ...
    		   state @a = ...
    		   state (@a) = ...
    		   (state @a) = ...
    		   state %a = ...
    		   state (%a) = ...
    		   (state %a) = ...
    		*/
    		yyerror(no_list_state);
    	    }
    	}
    
    	/* PL_generation sorcery:
    	 * an assignment like ($a,$b) = ($c,$d) is easier than
    	 * ($a,$b) = ($c,$a), since there is no need for temporary vars.
    	 * To detect whether there are common vars, the global var
    	 * PL_generation is incremented for each assign op we compile.
    	 * Then, while compiling the assign op, we run through all the
    	 * variables on both sides of the assignment, setting a spare slot
    	 * in each of them to PL_generation. If any of them already have
    	 * that value, we know we've got commonality.  We could use a
    	 * single bit marker, but then we'd have to make 2 passes, first
    	 * to clear the flag, then to test and set it.  To find somewhere
    	 * to store these values, evil chicanery is done with SvUVX().
    	 */
    
    	if (maybe_common_vars) {
    	    PL_generation++;
    	    if (aassign_common_vars(o))
    		o->op_private |= OPpASSIGN_COMMON;
    	    LINKLIST(o);
    	}
    
    	if (right && right->op_type == OP_SPLIT && !PL_madskills) {
    	    OP* tmpop = ((LISTOP*)right)->op_first;
    	    if (tmpop && (tmpop->op_type == OP_PUSHRE)) {
    		PMOP * const pm = (PMOP*)tmpop;
    		if (left->op_type == OP_RV2AV &&
    		    !(left->op_private & OPpLVAL_INTRO) &&
    		    !(o->op_private & OPpASSIGN_COMMON) )
    		{
    		    tmpop = ((UNOP*)left)->op_first;
    		    if (tmpop->op_type == OP_GV
    #ifdef USE_ITHREADS
    			&& !pm->op_pmreplrootu.op_pmtargetoff
    #else
    			&& !pm->op_pmreplrootu.op_pmtargetgv
    #endif
    			) {
    #ifdef USE_ITHREADS
    			pm->op_pmreplrootu.op_pmtargetoff
    			    = cPADOPx(tmpop)->op_padix;
    			cPADOPx(tmpop)->op_padix = 0;	/* steal it */
    #else
    			pm->op_pmreplrootu.op_pmtargetgv
    			    = MUTABLE_GV(cSVOPx(tmpop)->op_sv);
    			cSVOPx(tmpop)->op_sv = NULL;	/* steal it */
    #endif
    			pm->op_pmflags |= PMf_ONCE;
    			tmpop = cUNOPo->op_first;	/* to list (nulled) */
    			tmpop = ((UNOP*)tmpop)->op_first; /* to pushmark */
    			tmpop->op_sibling = NULL;	/* don't free split */
    			right->op_next = tmpop->op_next;  /* fix starting loc */
    			op_free(o);			/* blow off assign */
    			right->op_flags &= ~OPf_WANT;
    				/* "I don't know and I don't care." */
    			return right;
    		    }
    		}
    		else {
                       if (PL_modcount < RETURN_UNLIMITED_NUMBER &&
    		      ((LISTOP*)right)->op_last->op_type == OP_CONST)
    		    {
    			SV *sv = ((SVOP*)((LISTOP*)right)->op_last)->op_sv;
    			if (SvIOK(sv) && SvIVX(sv) == 0)
    			    sv_setiv(sv, PL_modcount+1);
    		    }
    		}
    	    }
    	}
    	return o;
        }
        if (!right)
    	right = newOP(OP_UNDEF, 0);
        if (right->op_type == OP_READLINE) {
    	right->op_flags |= OPf_STACKED;
    	return newBINOP(OP_NULL, flags, op_lvalue(scalar(left), OP_SASSIGN),
    		scalar(right));
        }
        else {
    	o = newBINOP(OP_SASSIGN, flags,
    	    scalar(right), op_lvalue(scalar(left), OP_SASSIGN) );
        }
        return o;
    }

注意那个OP.

\#define BASEOP \\  
OP\* op\_next; \\  
OP\* op\_sibling; \\  
OP\* (\*op\_ppaddr)(pTHX); \\  
MADPROP\_IN\_BASEOP \\  
PADOFFSET op\_targ; \\  
PERL\_BITFIELD16 op\_type:9; \\  
PERL\_BITFIELD16 op\_opt:1; \\  
PERL\_BITFIELD16 op\_latefree:1; \\  
PERL\_BITFIELD16 op\_latefreed:1; \\  
PERL\_BITFIELD16 op\_attached:1; \\  
PERL\_BITFIELD16 op\_spare:3; \\  
U8 op\_flags; \\  
U8 op\_private;  
\#endif

用来记录操作表达式。

因为我就写了一句话，后面什么也没干。

也就没什么可跟的了。

跟的过程中，可以清楚地看到，如果在lex中，没有找到什么yacc 感兴趣的东西，lex就把这些东西吞掉了。

主要就是这句：

parser->yychar = yylex();

===========

不过，perl的解释器的确是我所见过的最复杂的。

lex 会在开始前，和结束后，生成一些token，发给yacc。

这让我头大了许多。

先到这里吧。以后也不打算写了。实在累人。

[20140429104935593]: /images/20220824/8c8de8d195164c3ea4fc8195a50fc144.png
[20140429110320531]: /images/20220824/a91704da7ecf456ba8860adeef869c2e.png