PERL原码分析2

继续：

int Perl_yyparse (pTHX_ int gramtype){

??? register yy_parser *parser;?? ???? /* the parser object */

??? register yy_stack_frame? *ps;?? /* current parser stack frame */

----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。

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：

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,op_lvalue(scalar(left),optype),newUNOP(OP_SASSIGN,scalar(right)));
	}
	else {
	    return newBINOP(optype,OPf_STACKED,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,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
	 * ($a,$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,OP_SASSIGN),scalar(right));
    }
    else {
	o = newBINOP(OP_SASSIGN,scalar(right),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。