在内核中设备树的DTC将DTS、DTSi文件编译为DTB过程中使用了flex词法解析器和Bison语法分析器两种解析器，分析完这个是对这两种解析器会有更深刻和清晰的认识。
在学习和分析完DTC的源码后，再对DTC中词法分析器的源文件进行详细的分析。下面是DTC中Flex词法分析器的源代码：
/* SPDX-License-Identifier: GPL-2.0-or-later */
/** (C) Copyright David Gibson <dwg@au1.ibm.com>, IBM Corporation. 2005.
*/%option noyywrap nounput noinput never-interactive%x BYTESTRING
%x PROPNODENAME
%s V1PROPNODECHAR [a-zA-Z0-9,._+*#?@-]
PATHCHAR ({PROPNODECHAR}|[/])
LABEL [a-zA-Z_][a-zA-Z0-9_]*
STRING \"([^\\"]|\\.)*\"
CHAR_LITERAL '([^']|\\')*'
WS [[:space:]]
COMMENT "/*"([^*]|\*+[^*/])*\*+"/"
LINECOMMENT "//".*\n%{
#include "dtc.h"
#include "srcpos.h"
#include "dtc-parser.tab.h"extern bool treesource_error;/* CAUTION: this will stop working if we ever use yyless() or yyunput() */
#define YY_USER_ACTION \
{ \srcpos_update(&yylloc, yytext, yyleng); \
}/*#define LEXDEBUG 1*/#ifdef LEXDEBUG
#define DPRINT(fmt, ...) fprintf(stderr, fmt, ##__VA_ARGS__)
#else
#define DPRINT(fmt, ...) do { } while (0)
#endifstatic int dts_version = 1;#define BEGIN_DEFAULT() DPRINT("<V1>\n"); \BEGIN(V1); \static void push_input_file(const char *filename);
static bool pop_input_file(void);
static void PRINTF(1, 2) lexical_error(const char *fmt, ...);%}%%
<*>"/include/"{WS}*{STRING} {char *name = strchr(yytext, '\"') + 1;yytext[yyleng-1] = '\0';push_input_file(name);}<*>^"#"(line)?[ \t]+[0-9]+[ \t]+{STRING}([ \t]+[0-9]+)* {char *line, *fnstart, *fnend;struct data fn;/* skip text before line # */line = yytext;while (!isdigit((unsigned char)*line))line++;/* regexp ensures that first and list "* in the whole yytext are those at* beginning and end of the filename string */fnstart = memchr(yytext, '"', yyleng);for (fnend = yytext + yyleng - 1;*fnend != '"'; fnend--);assert(fnstart && fnend && (fnend > fnstart));fn = data_copy_escape_string(fnstart + 1,fnend - fnstart - 1);/* Don't allow nuls in filenames */if (memchr(fn.val, '\0', fn.len - 1))lexical_error("nul in line number directive");/* -1 since #line is the number of the next line */srcpos_set_line(xstrdup(fn.val), atoi(line) - 1);data_free(fn);}<*><<EOF>> {if (!pop_input_file()) {yyterminate();}}<*>{STRING} {DPRINT("String: %s\n", yytext);yylval.data = data_copy_escape_string(yytext+1,yyleng-2);return DT_STRING;}<*>"/dts-v1/" {DPRINT("Keyword: /dts-v1/\n");dts_version = 1;BEGIN_DEFAULT();return DT_V1;}<*>"/plugin/" {DPRINT("Keyword: /plugin/\n");return DT_PLUGIN;}<*>"/memreserve/" {DPRINT("Keyword: /memreserve/\n");BEGIN_DEFAULT();return DT_MEMRESERVE;}<*>"/bits/" {DPRINT("Keyword: /bits/\n");BEGIN_DEFAULT();return DT_BITS;}<*>"/delete-property/" {DPRINT("Keyword: /delete-property/\n");DPRINT("<PROPNODENAME>\n");BEGIN(PROPNODENAME);return DT_DEL_PROP;}<*>"/delete-node/" {DPRINT("Keyword: /delete-node/\n");DPRINT("<PROPNODENAME>\n");BEGIN(PROPNODENAME);return DT_DEL_NODE;}<*>"/omit-if-no-ref/" {DPRINT("Keyword: /omit-if-no-ref/\n");DPRINT("<PROPNODENAME>\n");BEGIN(PROPNODENAME);return DT_OMIT_NO_REF;}<*>{LABEL}: {DPRINT("Label: %s\n", yytext);yylval.labelref = xstrdup(yytext);yylval.labelref[yyleng-1] = '\0';return DT_LABEL;}<V1>([0-9]+|0[xX][0-9a-fA-F]+)(U|L|UL|LL|ULL)? {char *e;DPRINT("Integer Literal: '%s'\n", yytext);errno = 0;yylval.integer = strtoull(yytext, &e, 0);if (*e && e[strspn(e, "UL")]) {lexical_error("Bad integer literal '%s'",yytext);}if (errno == ERANGE)lexical_error("Integer literal '%s' out of range",yytext);else/* ERANGE is the only strtoull error triggerable* by strings matching the pattern */assert(errno == 0);return DT_LITERAL;}<*>{CHAR_LITERAL} {struct data d;DPRINT("Character literal: %s\n", yytext);d = data_copy_escape_string(yytext+1, yyleng-2);if (d.len == 1) {lexical_error("Empty character literal");yylval.integer = 0;} else {yylval.integer = (unsigned char)d.val[0];if (d.len > 2)lexical_error("Character literal has %d"" characters instead of 1",d.len - 1);}data_free(d);return DT_CHAR_LITERAL;}<*>\&{LABEL} { /* label reference */DPRINT("Ref: %s\n", yytext+1);yylval.labelref = xstrdup(yytext+1);return DT_LABEL_REF;}<*>"&{/"{PATHCHAR}*\} { /* new-style path reference */yytext[yyleng-1] = '\0';DPRINT("Ref: %s\n", yytext+2);yylval.labelref = xstrdup(yytext+2);return DT_PATH_REF;}<BYTESTRING>[0-9a-fA-F]{2} {yylval.byte = strtol(yytext, NULL, 16);DPRINT("Byte: %02x\n", (int)yylval.byte);return DT_BYTE;}<BYTESTRING>"]" {DPRINT("/BYTESTRING\n");BEGIN_DEFAULT();return ']';}<PROPNODENAME>\\?{PROPNODECHAR}+ {DPRINT("PropNodeName: %s\n", yytext);yylval.propnodename = xstrdup((yytext[0] == '\\') ?yytext + 1 : yytext);BEGIN_DEFAULT();return DT_PROPNODENAME;}"/incbin/" {DPRINT("Binary Include\n");return DT_INCBIN;}<*>{WS}+ /* eat whitespace */
<*>{COMMENT}+ /* eat C-style comments */
<*>{LINECOMMENT}+ /* eat C++-style comments */<*>"<<" { return DT_LSHIFT; };
<*>">>" { return DT_RSHIFT; };
<*>"<=" { return DT_LE; };
<*>">=" { return DT_GE; };
<*>"==" { return DT_EQ; };
<*>"!=" { return DT_NE; };
<*>"&&" { return DT_AND; };
<*>"||" { return DT_OR; };<*>. {DPRINT("Char: %c (\\x%02x)\n", yytext[0],(unsigned)yytext[0]);if (yytext[0] == '[') {DPRINT("<BYTESTRING>\n");BEGIN(BYTESTRING);}if ((yytext[0] == '{')|| (yytext[0] == ';')) {DPRINT("<PROPNODENAME>\n");BEGIN(PROPNODENAME);}return yytext[0];}%%static void push_input_file(const char *filename)
{assert(filename);srcfile_push(filename);yyin = current_srcfile->f;yypush_buffer_state(yy_create_buffer(yyin, YY_BUF_SIZE));
}static bool pop_input_file(void)
{if (srcfile_pop() == 0)return false;yypop_buffer_state();yyin = current_srcfile->f;return true;
}static void lexical_error(const char *fmt, ...)
{va_list ap;va_start(ap, fmt);srcpos_verror(&yylloc, "Lexical error", fmt, ap);va_end(ap);treesource_error = true;
}
Flex在SQL语法中使用的更多，在Verilog HDL硬件描述语言的编译过程中也使用，在各种计算机语言的编译过程中使用也很多。
后面开始Bison(Yacc)语法分析器的学习，并尽快完成DTC的分析(已分析完成内核对DTB文件的解析，以及时钟树对设备树的使用)。
