在阅读PHP源码的时候，会遇到很多诸如：CG()，EG() 这样的宏，如果不了解这些宏的意义，会给理解源码造成很大困难。

Zend引擎中有两个重要的全局变量结构体，就是Zend引擎关闭之前都会存在的变量：

typedef struct _zend_compiler_globals zend_compiler_globals;
typedef struct _zend_executor_globals zend_executor_globals;

/* Compiler */
#ifdef ZTS
# define CG(v) TSRMG(compiler_globals_id, zend_compiler_globals *, v)
int zendparse(void *compiler_globals);
#else
# define CG(v) (compiler_globals.v)
extern ZEND_API struct _zend_compiler_globals compiler_globals;
int zendparse(void);
#endif

/* Executor */
#ifdef ZTS
# define EG(v) TSRMG(executor_globals_id, zend_executor_globals *, v)
#else
# define EG(v) (executor_globals.v)
extern ZEND_API zend_executor_globals executor_globals;
#endif

CG 的含义就是 compiler_globals ，Zend编译器相关的全局变量；

EG 的含义就是 executor_globals，Zend执行器相关的全局变量；

这两个结构都包含了很多元素，对理解PHP内核有很重要的意义：

struct _zend_compiler_globals {
zend_stack bp_stack;
zend_stack switch_cond_stack;
zend_stack foreach_copy_stack;
zend_stack object_stack;
zend_stack declare_stack;

zend_class_entry *active_class_entry;

/* variables for list() compilation */
zend_llist list_llist;
zend_llist dimension_llist;
zend_stack list_stack;

zend_stack function_call_stack;

char *compiled_filename;

int zend_lineno;
int comment_start_line;
char *heredoc;
int heredoc_len;

zend_op_array *active_op_array;

HashTable *function_table; /* function symbol table */
HashTable *class_table; /* class table */

HashTable filenames_table;

HashTable *auto_globals;

zend_bool in_compilation;
zend_bool short_tags;
zend_bool asp_tags;
zend_bool allow_call_time_pass_reference;

zend_declarables declarables;

/* For extensions support */
zend_bool extended_info; /* generate extension information for debugger/profiler */
zend_bool handle_op_arrays; /* run op_arrays through op_array handlers */

zend_bool unclean_shutdown;

zend_bool ini_parser_unbuffered_errors;

zend_llist open_files;

long catch_begin;

struct _zend_ini_parser_param *ini_parser_param;

int interactive;

zend_uint start_lineno;
zend_bool increment_lineno;

znode implementing_class;

zend_uint access_type;

char *doc_comment;
zend_uint doc_comment_len;

#ifdef ZEND_MULTIBYTE
zend_encoding **script_encoding_list;
int script_encoding_list_size;
zend_bool detect_unicode;

zend_encoding *internal_encoding;

/* multibyte utility functions */
zend_encoding_detector encoding_detector;
zend_encoding_converter encoding_converter;
zend_encoding_oddlen encoding_oddlen;
#endif /* ZEND_MULTIBYTE */

#ifdef ZTS
HashTable **static_members;
int last_static_member;
#endif
};

struct _zend_executor_globals {
zval **return_value_ptr_ptr;

zval uninitialized_zval;
zval *uninitialized_zval_ptr;

zval error_zval;
zval *error_zval_ptr;

zend_function_state *function_state_ptr;
zend_ptr_stack arg_types_stack;

/* symbol table cache */
HashTable *symtable_cache[SYMTABLE_CACHE_SIZE];
HashTable **symtable_cache_limit;
HashTable **symtable_cache_ptr;

zend_op **opline_ptr;

HashTable *active_symbol_table;
HashTable symbol_table; /* main symbol table */

HashTable included_files; /* files already included */

jmp_buf *bailout;

int error_reporting;
int orig_error_reporting;
int exit_status;

zend_op_array *active_op_array;