macro_arg_subst

/* substitute args in macro_str and return allocated string */
static int *macro_arg_subst(Sym **nested_list, const int *macro_str, Sym *args)
{//
    int last_tok, t, spc;
    const int *st;
    Sym *s;
    CValue cval;
    TokenString str;
    CString cstr;

    tok_str_new(&str);
    //tok_print(macro_str);
    //assert(0);
    //mstr: d + s
    last_tok = 0;
    while(1) {
        TOK_GET(&t, &macro_str, &cval);
        if (!t)
            break;
        if (t == '#') {
            /* stringize */
            TOK_GET(&t, &macro_str, &cval);
            if (!t)
                break;
            s = sym_find2(args, t);
            if (s) {
                cstr_new(&cstr);
                st = s->d;
                spc = 0;
                while (*st) {
                    TOK_GET(&t, &st, &cval);
                    if (!check_space(t, &spc))
                        cstr_cat(&cstr, get_tok_str(t, &cval));
                }
                cstr.size -= spc;
                cstr_ccat(&cstr, '\0');
#ifdef PP_DEBUG
                printf("stringize: %s\n", (char *)cstr.data);
#endif
                /* add string */
                cval.cstr = &cstr;
                tok_str_add2(&str, TOK_STR, &cval);
                cstr_free(&cstr);
            } else {
                tok_str_add2(&str, t, &cval);
            }
        } else if (t >= TOK_IDENT) {
            //d + s, 第一次,  d
            s = sym_find2(args, t);
            if (s) {
                //yes, s is (the only) args of macro a
                //s->d: b(x)
                st = s->d;
                //tok_print(st);
                //assert(0);

                /* if '##' is present before or after, no arg substitution */
                if (*macro_str == TOK_TWOSHARPS || last_tok == TOK_TWOSHARPS) {
                    /* special case for var arg macros : ## eats the
                       ',' if empty VA_ARGS variable. */
                    /* XXX: test of the ',' is not 100%
                       reliable. should fix it to avoid security
                       problems */
                    if (gnu_ext && s->type.t &&
                        last_tok == TOK_TWOSHARPS &&
                        str.len >= 2 && str.str[str.len - 2] == ',') {
                        if (*st == 0) {
                            /* suppress ',' '##' */
                            str.len -= 2;
                        } else {
                            /* suppress '##' and add variable */
                            str.len--;
                            goto add_var;
                        }
                    } else {
                        int t1;
                    add_var:
                        for(;;) {
                            TOK_GET(&t1, &st, &cval);
                            if (!t1)
                                break;
                            tok_str_add2(&str, t1, &cval);
                        }
                    }
                } else {
                    /* NOTE: the stream cannot be read when macro
                       substituing an argument */
                    //b(x) 需要替换成 t + t1， 里面会继续替换为 ttt + t2
                    macro_subst(&str, nested_list, st, NULL);
                    //tok_print(str.str);assert(0);
                    // tok_print(str.str);
                    // assert(0);
                    // # 17 "t.c"
                    //
                    // tcc: tccpp.c:XXXX: macro_arg_subst: Assertion `0' failed.
                }
            } else {
                //如果不是参数，就直接加入就可以
                //#define a(d) d + s 中的s

                tok_str_add(&str, t);
            }
        } else {
            //参数必须是标示符 ' ', +属于这里
            tok_str_add2(&str, t, &cval);
        }
        last_tok = t;
    }
    tok_str_add(&str, 0);
    return str.str;
}