OS pre 知识点和解题过程分享

OS-pre

实验经验

建议用 vim，vim 有很多其他的功能可以用文件加入啊，nano虽然感觉没vim好用，但是软件工程基础还是要求使用nano的，用了vim命令显示未知指令，不过软工是GUI，实在不熟练也可以直接改文件，但是会卡。lab0 一定要熟练 grep、shell 和 Makefile 文件的创建，真的要熟练才能及时写好，不然实验很麻烦。Git 因为有软工第一次实验，所以其实还好。

C-exercise

认真阅读假期预习和 guide book，按照给的操作进入git仓库根目录也就是/24373433，再vim blib.c进入编辑就行，i进入插入模式。esc键退出，函数很简单，补充完整就好，然后make编译，再make run运行，出现 pass 就说明测试点过了，没过用 make dbg 调试一下就好了。

make-exercise

Makefile示例

 1CC := gcc
 2CFLAGS := -O2 -Wall
 3.PHONY: out clean case_add case_sub case_mul case_div case_all
 4# 用.PHONY避开文件存在的检查，伪目标，就不会检查同名文件是否存在。
 5casegen: casegen.c
 6	$(CC) $(CFLAGS) -o $@ $<
 7#gcc -O2 -Wall -o casegen casegen.c. $@=当前规则目标名，$<=第一个依赖文件
 8calc: calc.c
 9	$(CC) $(CFLAGS) -o $@ $<
10# 同上
11# 100 个加/减/乘/除样例，各自输出到对应文件
12case_add: casegen
13	./casegen add 100  > case_add
14
15case_sub: casegen
16	./casegen sub 100 > case_sub
17
18case_mul: casegen
19	./casegen mul 100  > case_mul
20
21case_div: casegen
22	./casegen div 100  > case_div
23# 这部分在下面分析casegen.c里详细讲述
24# 合并成 400 个样例
25case_all: case_add case_sub case_mul case_div
26	cat case_add case_sub case_mul case_div > case_all
27# make 或 make out：用 calc 计算 case_all，输出 out
28out: calc case_all
29	./calc < case_all > out
30# 默认目标
31all: out
32clean:
33	rm -f case_* out casegen calc

calc.c

 1#include <stdio.h>
 2#include <string.h>
 3  
 4int main() {
 5        char op[5];
 6        int a, b;
 7        while (scanf("%s%d%d", op, &a, &b) == 3) {
 8                if (!strcmp(op, "add")) {
 9                          printf("%d\n", a + b);
10                } else if (!strcmp(op, "sub")) {
11                         printf("%d\n", a - b);
12                } else if (!strcmp(op, "mul")) {
13                         printf("%d\n", a * b);
14                } else if (!strcmp(op, "div")) {
15                         printf("%d\n", a / b);
16                }
17        }
18        return 0;
19}

casegen.c

 1const char *ops[] = {"add", "sub", "mul", "div"};
 2
 3uint32_t xrand() {
 4        /* Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs" */
 5        static uint32_t x = 2024;
 6        x ^= x << 13;
 7        x ^= x >> 17;
 8        x ^= x << 5;
 9        return x;
10}
11
12void help() {
13        printf("Usage: ./casegen <op> <num>\n"
14               "Available <op>s: add, sub, mul, div.\n"
15               "<num>: The number of test cases generated (a positive integer).\n");
16}//这里写了命令的用法，usage：后面就是输出样例的指令，<op>表示操作名，<num>表示生成的个数，这就是为什么上面那么写
17
18int is_op_legal(char *op) {
19        size_t sz = sizeof(ops) / sizeof(ops[0]);
20        for (int i = 0; i < sz; i++) {
21                if (strcmp(op, ops[i]) == 0) {
22                        return 1;
23                }
24        }
25        return 0;
26}
27
28int get_num(char *str_num, int *num) {
29        *num = strtol(str_num, NULL, 10);
30        return *num > 0;
31}
32
33int main(int argc, char **argv) {
34        int num;
35        if (argc != 3 || !is_op_legal(argv[1]) || !get_num(argv[2], &num)) {
36                help();
37                return 1;
38        }
39        while (num--) {
40                printf("%s %u %u\n", argv[1], xrand() % 10000 + 1, xrand() % 10000 + 1);
41        }
42        return 0;
43}

mips-exercise

没有很多要说的，中文翻译过来一般都可以。

MIPS 汇编 (MARS)

 1#include <asm/asm.h>
 2.data
 3str:
 4.asciiz "Hello World\n"  # Null-terminated string "Hello World" stored at label 'str'
 5.align 2 # align to 4-byte boundary (2^2)
 6var:
 7.byte 3 # correctly aligned byte: 3
 8/* '<x>' 是需要替换的内容. */
 9/* use '.align <x>' to align the following words to 1-byte（希望是1字节一个对齐，所以就是.align 0） boundary (disabling word-alignment) */
10/* so that the byte 3 and word 7 is "connected" */
11/* Your code here. (1/6) */
12.align 0
13.word 7, 8, 9
14
15.text
16/* We define '_start_mips' here as the entry of our program. */
17EXPORT(_start_mips)
18.set at
19.set reorder
20        mtc0    zero, CP0_STATUS
21        li      sp, 0x84000000
22        /* Load the address of the string 'str' into the first parameter register. */
23        la      a0, str
24        /* use 'addiu  sp, sp, <x>' to push a proper-sized frame onto the stack for Nonleaf function 'print_str'. */
25        /* Your code here. (2/6) */
26        addiu sp,sp,-16
27        jal     print_str
28        /* use 'addiu  sp, sp, <x>' to restore stack pointer. */
29        /* Your code here. (3/6) */
30        addiu sp,sp,16
31        /* Set the first four parameters. */
32        li      a0, 0
33        li      a1, 1
34        li      a2, 2
35        li      a3, 3
36        /* use 'addiu  sp, sp, <x>' to push a proper-sized frame onto the stack for Nonleaf function 'hello'. */
37        /* Your code here. (4/6) */
38        addiu sp,sp,-24
39        lw      t1, var
40        li      t2, 5
41        /* use 'sw  t1, <x>(sp)' to store t1 at the proper place of the stack */
42        /* so that t1 is 5th argument of function hello. */
43        /* Your code here. (5/6) */
44        sw t1,16(sp)
45        /* use 'sw  t2, <x>(sp)' to store t2 at the proper place of the stack */
46        /* so that t2 is 6th argument of function hello. */
47        /* Your code here. (6/6) */
48        sw t2,20(sp)
49        /* use 'j' to call the function 'hello', we use 'j' instead of 'jal' because 'hello' is 'noreturn' */
50        j       hello

OS-pre#

实验经验#

C-exercise#

make-exercise#

mips-exercise#

OS-pre

实验经验

C-exercise

make-exercise

mips-exercise