QuickJS 操作码
司徒博容
QuickJS - 操作码
字节码
QuickJS执行JavaScript代码时，先将源码解析成字节码，然后再执行字节码。而字节码由操作码和操作数组成。操作码有点类似于汇编语言的指令，决定”CPU“执行何种操作。操作数就是操作码将要操作的数据。
操作码的生成
操作码在quickjs-opcode.h中定义。
/*
* QuickJS opcode definitions
*
* Copyright (c) 2017-2018 Fabrice Bellard
* Copyright (c) 2017-2018 Charlie Gordon
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#ifdef FMT
FMT(none)
FMT(none_int)
FMT(none_loc)
FMT(none_arg)
FMT(none_var_ref)
FMT(u8)
FMT(i8)
FMT(loc8)
FMT(const8)
FMT(label8)
FMT(u16)
FMT(i16)
FMT(label16)
FMT(npop)
FMT(npopx)
FMT(npop_u16)
FMT(loc)
FMT(arg)
FMT(var_ref)
FMT(u32)
FMT(i32)
FMT(const)
FMT(label)
FMT(atom)
FMT(atom_u8)
FMT(atom_u16)
FMT(atom_label_u8)
FMT(atom_label_u16)
FMT(label_u16)
#undef FMT
#endif /* FMT */
#ifdef DEF
#ifndef def
#define def(id, size, n_pop, n_push, f) DEF(id, size, n_pop, n_push, f)
#endif
DEF(invalid, 1, 0, 0, none) /* never emitted */
/* push values */
DEF( push_i32, 5, 0, 1, i32)
DEF( push_const, 5, 0, 1, const)
DEF( fclosure, 5, 0, 1, const) /* must follow push_const */
DEF(push_atom_value, 5, 0, 1, atom)
DEF( private_symbol, 5, 0, 1, atom)
DEF( undefined, 1, 0, 1, none)
DEF( null, 1, 0, 1, none)
DEF( push_this, 1, 0, 1, none) /* only used at the start of a function */
DEF( push_false, 1, 0, 1, none)
DEF( push_true, 1, 0, 1, none)
DEF( object, 1, 0, 1, none)
DEF( special_object, 2, 0, 1, u8) /* only used at the start of a function */
DEF( rest, 3, 0, 1, u16) /* only used at the start of a function */
DEF( drop, 1, 1, 0, none) /* a -> */
DEF( nip, 1, 2, 1, none) /* a b -> b */
DEF( nip1, 1, 3, 2, none) /* a b c -> b c */
DEF( dup, 1, 1, 2, none) /* a -> a a */
DEF( dup1, 1, 2, 3, none) /* a b -> a a b */
DEF( dup2, 1, 2, 4, none) /* a b -> a b a b */
DEF( dup3, 1, 3, 6, none) /* a b c -> a b c a b c */
DEF( insert2, 1, 2, 3, none) /* obj a -> a obj a (dup_x1) */
DEF( insert3, 1, 3, 4, none) /* obj prop a -> a obj prop a (dup_x2) */
DEF( insert4, 1, 4, 5, none) /* this obj prop a -> a this obj prop a */
DEF( perm3, 1, 3, 3, none) /* obj a b -> a obj b */
DEF( perm4, 1, 4, 4, none) /* obj prop a b -> a obj prop b */
DEF( perm5, 1, 5, 5, none) /* this obj prop a b -> a this obj prop b */
DEF( swap, 1, 2, 2, none) /* a b -> b a */
DEF( swap2, 1, 4, 4, none) /* a b c d -> c d a b */
DEF( rot3l, 1, 3, 3, none) /* x a b -> a b x */
DEF( rot3r, 1, 3, 3, none) /* a b x -> x a b */
DEF( rot4l, 1, 4, 4, none) /* x a b c -> a b c x */
DEF( rot5l, 1, 5, 5, none) /* x a b c d -> a b c d x */
DEF(call_constructor, 3, 2, 1, npop) /* func new.target args -> ret. arguments are not counted in n_pop */
DEF( call, 3, 1, 1, npop) /* arguments are not counted in n_pop */
DEF( tail_call, 3, 1, 0, npop) /* arguments are not counted in n_pop */
DEF( call_method, 3, 2, 1, npop) /* arguments are not counted in n_pop */
DEF(tail_call_method, 3, 2, 0, npop) /* arguments are not counted in n_pop */
DEF( array_from, 3, 0, 1, npop) /* arguments are not counted in n_pop */
DEF( apply, 3, 3, 1, u16)
DEF( return, 1, 1, 0, none)
DEF( return_undef, 1, 0, 0, none)
DEF(check_ctor_return, 1, 1, 2, none)
DEF( check_ctor, 1, 0, 0, none)
DEF( check_brand, 1, 2, 2, none) /* this_obj func -> this_obj func */
DEF( add_brand, 1, 2, 0, none) /* this_obj home_obj -> */
DEF( return_async, 1, 1, 0, none)
DEF( throw, 1, 1, 0, none)
DEF( throw_error, 6, 0, 0, atom_u8)
DEF( eval, 5, 1, 1, npop_u16) /* func args... -> ret_val */
DEF( apply_eval, 3, 2, 1, u16) /* func array -> ret_eval */
DEF( regexp, 1, 2, 1, none) /* create a RegExp object from the pattern and a
bytecode string */
DEF( get_super, 1, 1, 1, none)
DEF( import, 1, 1, 1, none) /* dynamic module import */
DEF( check_var, 5, 0, 1, atom) /* check if a variable exists */
DEF( get_var_undef, 5, 0, 1, atom) /* push undefined if the variable does not exist */
DEF( get_var, 5, 0, 1, atom) /* throw an exception if the variable does not exist */
DEF( put_var, 5, 1, 0, atom) /* must come after get_var */
DEF( put_var_init, 5, 1, 0, atom) /* must come after put_var. Used to initialize a global lexical variable */
DEF( put_var_strict, 5, 2, 0, atom) /* for strict mode variable write */
DEF( get_ref_value, 1, 2, 3, none)
DEF( put_ref_value, 1, 3, 0, none)
DEF( define_var, 6, 0, 0, atom_u8)
DEF(check_define_var, 6, 0, 0, atom_u8)
DEF( define_func, 6, 1, 0, atom_u8)
DEF( get_field, 5, 1, 1, atom)
DEF( get_field2, 5, 1, 2, atom)
DEF( put_field, 5, 2, 0, atom)
DEF( get_private_field, 1, 2, 1, none) /* obj prop -> value */
DEF( put_private_field, 1, 3, 0, none) /* obj value prop -> */
DEF(define_private_field, 1, 3, 1, none) /* obj prop value -> obj */
DEF( get_array_el, 1, 2, 1, none)
DEF( get_array_el2, 1, 2, 2, none) /* obj prop -> obj value */
DEF( put_array_el, 1, 3, 0, none)
DEF(get_super_value, 1, 3, 1, none) /* this obj prop -> value */
DEF(put_super_value, 1, 4, 0, none) /* this obj prop value -> */
DEF( define_field, 5, 2, 1, atom)
DEF( set_name, 5, 1, 1, atom)
DEF(set_name_computed, 1, 2, 2, none)
DEF( set_proto, 1, 2, 1, none)
DEF(set_home_object, 1, 2, 2, none)
DEF(define_array_el, 1, 3, 2, none)
DEF( append, 1, 3, 2, none) /* append enumerated object, update length */
DEF(copy_data_properties, 2, 3, 3, u8)
DEF( define_method, 6, 2, 1, atom_u8)
DEF(define_method_computed, 2, 3, 1, u8) /* must come after define_method */
DEF( define_class, 6, 2, 2, atom_u8) /* parent ctor -> ctor proto */
DEF( define_class_computed, 6, 3, 3, atom_u8) /* field_name parent ctor -> field_name ctor proto (class with computed name) */
DEF( get_loc, 3, 0, 1, loc)
DEF( put_loc, 3, 1, 0, loc) /* must come after get_loc */
DEF( set_loc, 3, 1, 1, loc) /* must come after put_loc */
DEF( get_arg, 3, 0, 1, arg)
DEF( put_arg, 3, 1, 0, arg) /* must come after get_arg */
DEF( set_arg, 3, 1, 1, arg) /* must come after put_arg */
DEF( get_var_ref, 3, 0, 1, var_ref)
DEF( put_var_ref, 3, 1, 0, var_ref) /* must come after get_var_ref */
DEF( set_var_ref, 3, 1, 1, var_ref) /* must come after put_var_ref */
DEF(set_loc_uninitialized, 3, 0, 0, loc)
DEF( get_loc_check, 3, 0, 1, loc)
DEF( put_loc_check, 3, 1, 0, loc) /* must come after get_loc_check */
DEF( put_loc_check_init, 3, 1, 0, loc)
DEF(get_var_ref_check, 3, 0, 1, var_ref)
DEF(put_var_ref_check, 3, 1, 0, var_ref) /* must come after get_var_ref_check */
DEF(put_var_ref_check_init, 3, 1, 0, var_ref)
DEF( close_loc, 3, 0, 0, loc)
DEF( if_false, 5, 1, 0, label)
DEF( if_true, 5, 1, 0, label) /* must come after if_false */
DEF( goto, 5, 0, 0, label) /* must come after if_true */
DEF( catch, 5, 0, 1, label)
DEF( gosub, 5, 0, 0, label) /* used to execute the finally block */
DEF( ret, 1, 1, 0, none) /* used to return from the finally block */
DEF( to_object, 1, 1, 1, none)
//DEF( to_string, 1, 1, 1, none)
DEF( to_propkey, 1, 1, 1, none)
DEF( to_propkey2, 1, 2, 2, none)
DEF( with_get_var, 10, 1, 0, atom_label_u8) /* must be in the same order as scope_xxx */
DEF( with_put_var, 10, 2, 1, atom_label_u8) /* must be in the same order as scope_xxx */
DEF(with_delete_var, 10, 1, 0, atom_label_u8) /* must be in the same order as scope_xxx */
DEF( with_make_ref, 10, 1, 0, atom_label_u8) /* must be in the same order as scope_xxx */
DEF( with_get_ref, 10, 1, 0, atom_label_u8) /* must be in the same order as scope_xxx */
DEF(with_get_ref_undef, 10, 1, 0, atom_label_u8)
DEF( make_loc_ref, 7, 0, 2, atom_u16)
DEF( make_arg_ref, 7, 0, 2, atom_u16)
DEF(make_var_ref_ref, 7, 0, 2, atom_u16)
DEF( make_var_ref, 5, 0, 2, atom)
DEF( for_in_start, 1, 1, 1, none)
DEF( for_of_start, 1, 1, 3, none)
DEF(for_await_of_start, 1, 1, 3, none)
DEF( for_in_next, 1, 1, 3, none)
DEF( for_of_next, 2, 3, 5, u8)
DEF(iterator_check_object, 1, 1, 1, none)
DEF(iterator_get_value_done, 1, 1, 2, none)
DEF( iterator_close, 1, 3, 0, none)
DEF(iterator_close_return, 1, 4, 4, none)
DEF( iterator_next, 1, 4, 4, none)
DEF( iterator_call, 2, 4, 5, u8)
DEF( initial_yield, 1, 0, 0, none)
DEF( yield, 1, 1, 2, none)
DEF( yield_star, 1, 1, 2, none)
DEF(async_yield_star, 1, 1, 2, none)
DEF( await, 1, 1, 1, none)
/* arithmetic/logic operations */
DEF( neg, 1, 1, 1, none)
DEF( plus, 1, 1, 1, none)
DEF( dec, 1, 1, 1, none)
DEF( inc, 1, 1, 1, none)
DEF( post_dec, 1, 1, 2, none)
DEF( post_inc, 1, 1, 2, none)
DEF( dec_loc, 2, 0, 0, loc8)
DEF( inc_loc, 2, 0, 0, loc8)
DEF( add_loc, 2, 1, 0, loc8)
DEF( not, 1, 1, 1, none)
DEF( lnot, 1, 1, 1, none)
DEF( typeof, 1, 1, 1, none)
DEF( delete, 1, 2, 1, none)
DEF( delete_var, 5, 0, 1, atom)
DEF( mul, 1, 2, 1, none)
DEF( div, 1, 2, 1, none)
DEF( mod, 1, 2, 1, none)
DEF( add, 1, 2, 1, none)
DEF( sub, 1, 2, 1, none)
DEF( pow, 1, 2, 1, none)
DEF( shl, 1, 2, 1, none)
DEF( sar, 1, 2, 1, none)
DEF( shr, 1, 2, 1, none)
DEF( lt, 1, 2, 1, none)
DEF( lte, 1, 2, 1, none)
DEF( gt, 1, 2, 1, none)
DEF( gte, 1, 2, 1, none)
DEF( instanceof, 1, 2, 1, none)
DEF( in, 1, 2, 1, none)
DEF( eq, 1, 2, 1, none)
DEF( neq, 1, 2, 1, none)
DEF( strict_eq, 1, 2, 1, none)
DEF( strict_neq, 1, 2, 1, none)
DEF( and, 1, 2, 1, none)
DEF( xor, 1, 2, 1, none)
DEF( or, 1, 2, 1, none)
DEF(is_undefined_or_null, 1, 1, 1, none)
#ifdef CONFIG_BIGNUM
DEF( mul_pow10, 1, 2, 1, none)
DEF( math_mod, 1, 2, 1, none)
#endif
/* must be the last non short and non temporary opcode */
DEF( nop, 1, 0, 0, none)
/* temporary opcodes: never emitted in the final bytecode */
def( enter_scope, 3, 0, 0, u16) /* emitted in phase 1, removed in phase 2 */
def( leave_scope, 3, 0, 0, u16) /* emitted in phase 1, removed in phase 2 */
def( label, 5, 0, 0, label) /* emitted in phase 1, removed in phase 3 */
def(scope_get_var_undef, 7, 0, 1, atom_u16) /* emitted in phase 1, removed in phase 2 */
def( scope_get_var, 7, 0, 1, atom_u16) /* emitted in phase 1, removed in phase 2 */
def( scope_put_var, 7, 1, 0, atom_u16) /* emitted in phase 1, removed in phase 2 */
def(scope_delete_var, 7, 0, 1, atom_u16) /* emitted in phase 1, removed in phase 2 */
def( scope_make_ref, 11, 0, 2, atom_label_u16) /* emitted in phase 1, removed in phase 2 */
def( scope_get_ref, 7, 0, 2, atom_u16) /* emitted in phase 1, removed in phase 2 */
def(scope_put_var_init, 7, 0, 2, atom_u16) /* emitted in phase 1, removed in phase 2 */
def(scope_get_private_field, 7, 1, 1, atom_u16) /* obj -> value, emitted in phase 1, removed in phase 2 */
def(scope_get_private_field2, 7, 1, 2, atom_u16) /* obj -> obj value, emitted in phase 1, removed in phase 2 */
def(scope_put_private_field, 7, 1, 1, atom_u16) /* obj value ->, emitted in phase 1, removed in phase 2 */
def( set_class_name, 5, 1, 1, u32) /* emitted in phase 1, removed in phase 2 */
def( line_num, 5, 0, 0, u32) /* emitted in phase 1, removed in phase 3 */
#if SHORT_OPCODES
DEF( push_minus1, 1, 0, 1, none_int)
DEF( push_0, 1, 0, 1, none_int)
DEF( push_1, 1, 0, 1, none_int)
DEF( push_2, 1, 0, 1, none_int)
DEF( push_3, 1, 0, 1, none_int)
DEF( push_4, 1, 0, 1, none_int)
DEF( push_5, 1, 0, 1, none_int)
DEF( push_6, 1, 0, 1, none_int)
DEF( push_7, 1, 0, 1, none_int)
DEF( push_i8, 2, 0, 1, i8)
DEF( push_i16, 3, 0, 1, i16)
DEF( push_const8, 2, 0, 1, const8)
DEF( fclosure8, 2, 0, 1, const8) /* must follow push_const8 */
DEF(push_empty_string, 1, 0, 1, none)
DEF( get_loc8, 2, 0, 1, loc8)
DEF( put_loc8, 2, 1, 0, loc8)
DEF( set_loc8, 2, 1, 1, loc8)
DEF( get_loc0, 1, 0, 1, none_loc)
DEF( get_loc1, 1, 0, 1, none_loc)
DEF( get_loc2, 1, 0, 1, none_loc)
DEF( get_loc3, 1, 0, 1, none_loc)
DEF( put_loc0, 1, 1, 0, none_loc)
DEF( put_loc1, 1, 1, 0, none_loc)
DEF( put_loc2, 1, 1, 0, none_loc)
DEF( put_loc3, 1, 1, 0, none_loc)
DEF( set_loc0, 1, 1, 1, none_loc)
DEF( set_loc1, 1, 1, 1, none_loc)
DEF( set_loc2, 1, 1, 1, none_loc)
DEF( set_loc3, 1, 1, 1, none_loc)
DEF( get_arg0, 1, 0, 1, none_arg)
DEF( get_arg1, 1, 0, 1, none_arg)
DEF( get_arg2, 1, 0, 1, none_arg)
DEF( get_arg3, 1, 0, 1, none_arg)
DEF( put_arg0, 1, 1, 0, none_arg)
DEF( put_arg1, 1, 1, 0, none_arg)
DEF( put_arg2, 1, 1, 0, none_arg)
DEF( put_arg3, 1, 1, 0, none_arg)
DEF( set_arg0, 1, 1, 1, none_arg)
DEF( set_arg1, 1, 1, 1, none_arg)
DEF( set_arg2, 1, 1, 1, none_arg)
DEF( set_arg3, 1, 1, 1, none_arg)
DEF( get_var_ref0, 1, 0, 1, none_var_ref)
DEF( get_var_ref1, 1, 0, 1, none_var_ref)
DEF( get_var_ref2, 1, 0, 1, none_var_ref)
DEF( get_var_ref3, 1, 0, 1, none_var_ref)
DEF( put_var_ref0, 1, 1, 0, none_var_ref)
DEF( put_var_ref1, 1, 1, 0, none_var_ref)
DEF( put_var_ref2, 1, 1, 0, none_var_ref)
DEF( put_var_ref3, 1, 1, 0, none_var_ref)
DEF( set_var_ref0, 1, 1, 1, none_var_ref)
DEF( set_var_ref1, 1, 1, 1, none_var_ref)
DEF( set_var_ref2, 1, 1, 1, none_var_ref)
DEF( set_var_ref3, 1, 1, 1, none_var_ref)
DEF( get_length, 1, 1, 1, none)
DEF( if_false8, 2, 1, 0, label8)
DEF( if_true8, 2, 1, 0, label8) /* must come after if_false8 */
DEF( goto8, 2, 0, 0, label8) /* must come after if_true8 */
DEF( goto16, 3, 0, 0, label16)
DEF( call0, 1, 1, 1, npopx)
DEF( call1, 1, 1, 1, npopx)
DEF( call2, 1, 1, 1, npopx)
DEF( call3, 1, 1, 1, npopx)
DEF( is_undefined, 1, 1, 1, none)
DEF( is_null, 1, 1, 1, none)
DEF(typeof_is_undefined, 1, 1, 1, none)
DEF( typeof_is_function, 1, 1, 1, none)
#endif
#undef DEF
#undef def
#endif /* DEF */
只看这个文件，并不能很好的理解操作码是如何生成的。因为，这个文件中并未定义FMT和DEF宏定义。而QuickJS代码巧妙的使用了宏定义。通过更改宏定义的定义，实现同一份代码完成多个定义。这招叫做一鱼多吃，实在是妙。
字节码的定义在quickjs.c文件中。
typedef struct JSOpCode {
#ifdef DUMP_BYTECODE
const char *name;
#endif
uint8_t size; /* in bytes */
/* the opcodes remove n_pop items from the top of the stack, then
pushes n_push items */
uint8_t n_pop;
uint8_t n_push;
uint8_t fmt;
} JSOpCode;
static const JSOpCode opcode_info[OP_COUNT + (OP_TEMP_END - OP_TEMP_START)] = {
#define FMT(f)
#ifdef DUMP_BYTECODE
#define DEF(id, size, n_pop, n_push, f) { #id, size, n_pop, n_push, OP_FMT_ ## f },
#else
#define DEF(id, size, n_pop, n_push, f) { size, n_pop, n_push, OP_FMT_ ## f },
#endif
#include "quickjs-opcode.h"
#undef DEF
#undef FMT
};
程序的开始，定义了一个JSOpCode结构体，每个操作码使用JSOpCode表示。这个结构体中，定义了操作码名称、操作码加其后面操作数总长度（单位是byte，如：如果是5，则表示操作码加操作数总共是5bytpe，代码执行时根据这个来做PC偏移的）、该操作码执行时会出栈或入栈多少个项（根据其操作数的个数决定）以及其操作对象的格式。
当QuickJS被编译器编译时，首先会对其源码进行预编译。在预编译过程中，根据宏定义，将会完成对opcode_info的定义。预编译之后，opcode_info将会变成下面代码：
static const JSOpCode opcode_info[OP_COUNT + (OP_TEMP_END - OP_TEMP_START)] = {
{"invalid",1,0,0,OP_FMT_none},
{"push_i32",5,0,1,OP_FMT_i32},
······
{"typeof_is_function", 1, 1, 1, OP_FMT_none}
};
那么为什么是这样的呢？
解释前，先复习下宏定义。宏定义的存活于编译的预处理中。 宏定义中有两个运算符：#和##。#运算符将一个宏的参数转换为字符串字面量。##运算符可以将两个记号（例如标识符）“粘”在一起，成为一个记号。（##运算符被称为“记号粘合”）。举个例子：
#define STR(s) #s
#define CONS(a,b) int(a##e##b)
int main(){
printf(STR(vck));
printf("%d/n", CONS(2,3));
return 0;
}
以上代码预处理之后，将会变成这样
int main(){
printf("vck");
printf("%d/n", 2e3);
return 0;
}
我们可以看到，STR宏定义的作用，就是将其参数转换成字符串字面量；而CONS宏定义的作用就是将其参数连接起来。
回到opcode_info的定义上来。首先，先定义了它作为一个数组。数组的长度是：OP_COUNT + (OP_TEMP_END - OP_TEMP_START) 。然后就是数组的定义。首先定义FMT(f)为空，然后根据是否定义了DUMP_BYTECODE来对DEF进行不同的定义。DEF的这两个不同定义的区别是：是否存在name这个字段。两种定义摘出来如下
//第一种
#define DEF(id, size, n_pop, n_push, f) { #id, size, n_pop, n_push, OP_FMT_ ## f },
//第二种
#define DEF(id, size, n_pop, n_push, f) { size, n_pop, n_push, OP_FMT_ ## f },
这两个宏定义可以看出来，都是定义一个结构体。这个结构体，就是我们文章一开始说的操作码–JSOpCode。
接下来，通过 #include “quickjs-opcode.h” 引入了操作码定义文件。在这里，为了便于解释，我们选择DEF的第一种宏定义来进行解释。
在操作码定义头文件中，首先是使用FMT来定义一些操作数格式。当然，在这个场景中，我们的FMT定义为空，因此，FMT定义的所有语句都是无效的，不会生成代码。
接下来是使用DEF定义了一些语句。根据它的宏定义含义，那么第一行定义（如下：）
DEF(invalid, 1, 0, 0, none)
将会生成如下代码：
{"invalid", 1, 0, 0, OP_FMT_none},
同样，第二行代码(如下：)
DEF( push_i32, 5, 0, 1, i32)
会生成如下代码：
{"push_i32", 5, 0, 1, OP_FMT_i32}，
同样，以此类推，预编译之后最终将会生成如下的代码
static const JSOpCode opcode_info[OP_COUNT + (OP_TEMP_END - OP_TEMP_START)] =
{
{"invalid",1,0,0,OP_FMT_none},
{"push_i32",5,0,1,OP_FMT_i32},
······
{"typeof_is_function", 1, 1, 1, OP_FMT_none}
}
操作数格式
在操作码中，定义了fmt字段。该字段的含义是标明操作码操作的操作数是什么格式。比如：如果是32bit的整数，则其值为OP_FMT_i32。OP_FMT_i32是怎么来的呢？也是通过宏定义生成的。它是一个枚举类型。定义代码如下：
//定义opcodeFormat枚举，例如：OP_FMT_none OP_FMT_none_int OP_FMT_none_loc
typedef enum OPCodeFormat {
#define FMT(f) OP_FMT_ ## f,
#define DEF(id, size, n_pop, n_push, f)
#include "quickjs-opcode.h"
#undef DEF
#undef FMT
} OPCodeFormat;
在这个枚举定义中，我们首先定义了FMT的定义，其定义为
#define FMT(f) OP_FMT_ ## f,
接下来，这次与上面操作码的定义不同，定义DEF为空。
#define DEF(id, size, n_pop, n_push, f)
同样，通过引入 #include “quickjs-opcode.h” 头文件来定义操作数格式。这次，我们就不仔细解释了。预处理之后的代码如下：
typedef enum OPCodeFormat {
OP_FMT_none,
OP_FMT_none_int,
......
OP_FMT_i32,
......
OP_FMT_label_u16
} OPCodeFormat;
操作码的种类
操作码决定了”CPU“做何种操作。我们可以将这些操作码分成如下几类：
变量操作相关指令
- define_var, define_func, define_class, define_field, define_method…
- (get | put | set)_(loc | arg | var_ref | var | field | array_el…)
调用相关指令
- call, tail_call, call_method, tail_call_method, return…
跳转相关指令
- goto, if_false, if_true, label…
指令变换相关指令
- drop, nip, dup, insert, perm, swap, rot…
数据相关指令
- push, object, array_from…
欢迎转载，请注明出处
类似资料：