vld功能的實現要依賴 Zend引擎初始化(zend_startup)的時候 將zend_execute和zend_compile_file定義為函式指標的功勞了  

預設的

zend_execute指向execute

zend_compile_file指向compile_file

試想如果我們在實際編譯和執行之前將zend_execute和zend_compile_file重寫為其他的編譯和執行函式，我們不就可以乾點什麼事嗎

vld正是由此思路實現的 ,在每次請求初始化的鉤子函式（PHP_RINIT_FUNCTION）中，將zend_execute和zend_compile_file替換成自己的vld_execute和vld_compile_file，這兩個函式其實是對原始函式進行了封裝，添加了輸出opcode資訊的附加功能，因為引擎初始化是發生在模組請求初始化之前，而模組請求初始化又是在編譯和執行之前，這樣就實現了檢視opcode的功能。

基本思路瞭解清楚，下面我們就看程式碼實現部分：

原本zend_compile_file zend_compile_string還是要執行的

static zend_op_array* (*old_compile_file)(zend_file_handle* file_handle, int type TSRMLS_DC);
static zend_op_array* vld_compile_file(zend_file_handle*, int TSRMLS_DC);

static zend_op_array* (*old_compile_string)(zval *source_string, char *filename TSRMLS_DC);
static zend_op_array* vld_compile_string(zval *source_string, char *filename TSRMLS_DC);

#if PHP_VERSION_ID >= 50500
static void (*old_execute_ex)(zend_execute_data *execute_data TSRMLS_DC);
static void vld_execute_ex(zend_execute_data *execute_data TSRMLS_DC);
#else
static void (*old_execute)(zend_op_array *op_array TSRMLS_DC);
static void vld_execute(zend_op_array *op_array TSRMLS_DC);
#endif
 

PHP_RINIT_FUNCTION(vld)
{
	/* 記錄下原本的zend_compile_file, zend_compile_string, zend_execute_ex */
	old_compile_file = zend_compile_file;
#if (PHP_MAJOR_VERSION > 5) || (PHP_MAJOR_VERSION == 5 && PHP_MINOR_VERSION >= 2)
	old_compile_string = zend_compile_string;
#endif
#if PHP_VERSION_ID >= 50500
	old_execute_ex = zend_execute_ex;
#else
	old_execute = zend_execute;
#endif

	/* 如果啟用vld掛鉤 */
	if (VLD_G(active)) {
		/* 使用 自定義的 vld_compile_file */
		zend_compile_file = vld_compile_file;
#if (PHP_MAJOR_VERSION > 5) || (PHP_MAJOR_VERSION == 5 && PHP_MINOR_VERSION >= 2)
		/* 使用 自定義的 vld_compile_string */
		zend_compile_string = vld_compile_string;
#endif
		/* 是否執行php指令碼 */
		if (!VLD_G(execute)) {
#if PHP_VERSION_ID >= 50500
			zend_execute_ex = vld_execute_ex;
#else
			zend_execute = vld_execute;
#endif
		}
	}

	/* 是否輸出至檔案 */
	if (VLD_G(save_paths)) {
		char *filename;

		filename = malloc(strlen("paths.dot") + strlen(VLD_G(save_dir)) + 2);
		sprintf(filename, "%s/%s", VLD_G(save_dir), "paths.dot");

		VLD_G(path_dump_file) = fopen(filename, "w");
		free(filename);

		if (VLD_G(path_dump_file)) {
			fprintf(VLD_G(path_dump_file), "digraph {\n");
		}
	}
	return SUCCESS;
}
 

vld_compile_file---------------->old_compile_file--------------->vld_dump_oparray

vld_compile_string------------->old_compile_file--------------->vld_dump_oparray

我們來看看vld_dump_oparray

void vld_dump_oparray(zend_op_array *opa TSRMLS_DC)
{
	unsigned int i;
	vld_set *set;
	vld_branch_info *branch_info;
	unsigned int base_address = (unsigned int)(zend_intptr_t)&(opa->opcodes[0]);

	set = vld_set_create(opa->last);
	branch_info = vld_branch_info_create(opa->last);

	if (VLD_G(dump_paths)) {
		vld_analyse_oparray(opa, set, branch_info TSRMLS_CC);
	}
	if (VLD_G(format)) {
		vld_printf (stderr, "filename:%s%s\n", VLD_G(col_sep), ZSTRING_VALUE(opa->filename));
		vld_printf (stderr, "function name:%s%s\n", VLD_G(col_sep), ZSTRING_VALUE(opa->function_name));
		vld_printf (stderr, "number of ops:%s%d\n", VLD_G(col_sep), opa->last);
	} else {
		vld_printf (stderr, "filename:       %s\n", ZSTRING_VALUE(opa->filename));
		vld_printf (stderr, "function name:  %s\n", ZSTRING_VALUE(opa->function_name));
		vld_printf (stderr, "number of ops:  %d\n", opa->last);
	}
#ifdef IS_CV /* PHP >= 5.1 */
	vld_printf (stderr, "compiled vars:  ");
	for (i = 0; i < opa->last_var; i++) {
		vld_printf (stderr, "!%d = $%s%s", i, OPARRAY_VAR_NAME(opa->vars[i]), ((i + 1) == opa->last_var) ? "\n" : ", ");
	}
	if (!opa->last_var) {
		vld_printf(stderr, "none\n");
	}
#endif
	if (VLD_G(format)) {
		vld_printf(stderr, "line%s# *%s%s%sop%sfetch%sext%sreturn%soperands\n",VLD_G(col_sep),VLD_G(col_sep),VLD_G(col_sep),VLD_G(col_sep),VLD_G(col_sep),VLD_G(col_sep),VLD_G(col_sep),VLD_G(col_sep));
	} else {
		vld_printf(stderr, "line     #* E I O op                           fetch          ext  return  operands\n");
		vld_printf(stderr, "-------------------------------------------------------------------------------------\n");
	}
	/* 遍歷opcode */
	for (i = 0; i < opa->last; i++) {
		vld_dump_op(i, opa->opcodes, base_address, vld_set_in(set, i), vld_set_in(branch_info->entry_points, i), vld_set_in(branch_info->starts, i), vld_set_in(branch_info->ends, i), opa TSRMLS_CC);
	}
	vld_printf(stderr, "\n");

	if (VLD_G(dump_paths)) {
		vld_branch_post_process(opa, branch_info);
		vld_branch_find_paths(branch_info);
		vld_branch_info_dump(opa, branch_info TSRMLS_CC);
	}

	vld_set_free(set);
	vld_branch_info_free(branch_info);
}

最後在請求結束後 要恢復原本的指標函式

PHP_RSHUTDOWN_FUNCTION(vld)
{
	zend_compile_file = old_compile_file;
#if PHP_VERSION_ID >= 50500
	zend_execute_ex   = old_execute_ex;
#else
	zend_execute      = old_execute;
#endif

	if (VLD_G(path_dump_file)) {
		fprintf(VLD_G(path_dump_file), "}\n");
		fclose(VLD_G(path_dump_file));
	}

	return SUCCESS;
}