PHP7 Kernel Analysis 5 Compilation of PHP Code

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1.Compilation of PHP code

The task of PHP's parsing process is to convert the PHP code into an opcode array. All the information in the code is saved in the opcode array, and then the opcode array is handed over to the zend engine for execution. The opcode is specifically executed by the kernel. Commands, such as assignment, addition and subtraction operations, function calls, etc. Each opcode corresponds to a processing handle. These handlers are C functions defined in advance.

##2.PHP code->Abstract Syntax Tree (AST)

PHP使用re2c、bison完成这个阶段的工作:
    re2c: 词法分析器，将输入分割为一个个有意义的词块，称为token
    bison: 语法分析器，确定词法分析器分割出的token是如何彼此关联的

词法、语法解析过程

1.yyparse(zendparse)调用yylex(zendlex)，当读取到一个合法的token时，返回值为token类型
2.yylex调用lex_scan读取合法的token值
3.yyparse将token类型与token值构造抽象语法树,最后将根节点保存到CG(compiler_globals ，Zend编译器相关的全局变量)的ast中

##3.AST node structure

typedef struct _zend_ast   zend_ast;

//普通节点类型
struct _zend_ast {
    zend_ast_kind kind;  //节点类型
    zend_ast_attr attr;  //节点附加属性
    uint32_t lineno;    //行号
    zend_ast *child[1];  //子节点数组
};

//普通节点类型，但有子节点的个数
typedef struct _zend_ast_list {
    zend_ast_kind kind; //节点类型
    zend_ast_attr attr; //节点附加属性
    uint32_t lineno; //行号
    uint32_t children; //子节点数量
    zend_ast *child[1];//子节点数组
} zend_ast_list;

//函数、类的ast节点结构
typedef struct _zend_ast_decl {
    zend_ast_kind kind; //节点类型
    zend_ast_attr attr; //节点附加属性
    uint32_t start_lineno; //开始行号
    uint32_t end_lineno;   //结束行号
    uint32_t flags;
    unsigned char *lex_pos;
    zend_string *doc_comment;
    zend_string *name;
    zend_ast *child[4]; //类中会将继承的父类、实现的接口以及类中的语句解析保存在child中
} zend_ast_decl;

实例:
$a = 123;
$b = "hi~";

echo $a,$b;

#4.zend_op_array

##

zend_op *opcodes; //opcode指令数组
zval *literals; //字面量(常量)数组，这些都是在PHP代码定义的一些值
zend_string **vars; //PHP变量名数组,根据变量编号可以获取相应的变量

//opcode指令结构
struct _zend_op {
    const void *handler; //指令执行handler
    znode_op op1;   //操作数1
    znode_op op2;   //操作数2
    znode_op result; //返回值
    uint32_t extended_value; 
    uint32_t lineno; 
    zend_uchar opcode;  //opcode指令
    zend_uchar op1_type; //操作数1类型
    zend_uchar op2_type; //操作数2类型
    zend_uchar result_type; //返回值类型
};

5.handler processing function

handler is the processing process written in C language corresponding to each opcode, and the processing process corresponding to all opcodes Defined in zend_vm_def.h, the opcode processing process has three different forms: CALL, SWITCH, GOTO. The default method is CALL

CALL:把每种opcode负责的工作封装成不同的function，然后执行器循环调用执行
SWITCH:把所有的处理方式写到一个switch下，然后通过case不同的opcode执行具体的操作
GOTO:把所有opcode的处理方式通过C语言里面的label标签区分开，然后执行器执行的时候goto到相应的位置处理

6. Abstract Syntax tree->Opcodes

void zend_compile_top_stmt(zend_ast *ast){
    ....
    if (ast->kind == ZEND_AST_STMT_LIST) { //第一次进来一定是这种类型
        zend_ast_list *list = zend_ast_get_list(ast);
        uint32_t i;
        for (i = 0; i < list->children; ++i) {
            zend_compile_top_stmt(list->child[i]);//list各child语句相互独立，递归编译
        }
        return;
    }
    //各语句编译入口
    zend_compile_stmt(ast);
    ....
}

1.zend_compile_top_stmt接收语法树，首先判断节点类型是否为ZEND_AST_STMT_LIST(表示当前节点下
有多个独立的节点),若是则进行递归
2.当递归结束后，调用zend_compile_stmt进行编译成opcodes

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