1 RISC-V assembly (easy)<\/h2>\n\n\u9605\u8bfbuser\/call.asm<\/code>\uff0c\u56de\u7b54\u4e0b\u5217\u95ee\u9898\u3002<\/p>\n<\/blockquote>\n\n- Which registers contain arguments to functions? For example, which register holds 13 in main’s call to
printf<\/code>?<\/li>\n<\/ol>\nmain<\/code>\u51fd\u6570\u8c03\u7528printf<\/code>\u51fd\u6570\u65f6\u5c31\u5c06\u4e09\u4e2a\u53c2\u6570\u4fdd\u5b58\u5728\u4e86a0, a1, a2<\/code>\u4e2d\uff0c\u5176\u4e2d13\uff08\u7b2c3\u4e2a\u53c2\u6570\uff09\u4fdd\u5b58\u5728\u4e86a2<\/code>\u5bc4\u5b58\u5668\u4e2d\u3002<\/p>\nvoid main(void) {\n 1c: 1141 addi sp,sp,-16\n 1e: e406 sd ra,8(sp)\n 20: e022 sd s0,0(sp)\n 22: 0800 addi s0,sp,16\n printf("%d %d\\n", f(8)+1, 13);\n 24: 4635 li a2,13\n 26: 45b1 li a1,12\n 28: 00000517 auipc a0,0x0\n 2c: 7c850513 addi a0,a0,1992 # 7f0 <malloc+0xe8>\n 30: 00000097 auipc ra,0x0\n 34: 61a080e7 jalr 1562(ra) # 64a <printf>\n exit(0);\n 38: 4501 li a0,0\n 3a: 00000097 auipc ra,0x0\n 3e: 298080e7 jalr 664(ra) # 2d2 <exit><\/code><\/pre>\n\n- Where is the call to function
f<\/code> in the assembly code for main? Where is the call to g<\/code>? (Hint: the compiler may inline functions.)<\/li>\n<\/ol>\nmain<\/code>\u4e2d\u5728\u8c03\u7528printf<\/code>\u51fd\u6570\u7684\u65f6\u5019\uff0c\u4f20\u9012\u53c2\u6570\u65f6\u8c03\u7528\u4e86f<\/code>\u51fd\u6570\uff0c\u540c\u65f6f<\/code>\u51fd\u6570\u5728\u8fd4\u56de\u7684\u65f6\u5019\u8c03\u7528\u4e86g<\/code>\u51fd\u6570\u3002<\/p>\nint f(int x) {\n e: 1141 addi sp,sp,-16\n 10: e422 sd s0,8(sp)\n 12: 0800 addi s0,sp,16\n return g(x);\n}<\/code><\/pre>\n\n- At what address is the function
printf<\/code> located?<\/li>\n<\/ol>\n000000000000064a <printf>:<\/code><\/p>\n\n- What value is in the register
ra<\/code> just after the jalr<\/code> to printf<\/code> in main<\/code>?<\/li>\n<\/ol>\n\u6839\u636eRISC-V ISA<\/code>\u7684jalr<\/code>\u6307\u4ee4\u7684\u4f5c\u7528\uff0c\u4f1a\u5c06\u4e0b\u4e00\u6761\u6307\u4ee4\u7684\u5730\u5740\u4fdd\u5b58\u5728\u5bc4\u5b58\u5668ra<\/code>\u91cc\uff0c\u6240\u4ee5ra<\/code>\u7684\u503c\u662f0x38<\/code>\u3002<\/p>\n\n- \n
Run the following code.<\/p>\n
unsigned int i = 0x00646c72;\nprintf(\"H%x Wo%s\", 57616, &i);\n<\/code><\/pre>\nWhat is the output? <\/p>\n<\/li>\n<\/ol>\n
HE110 World\uff0c 57616\u7684\u5341\u516d\u8fdb\u5236\u6570\u503c0xE110<\/code>\uff0cr\u5bf9\u5e94\u7684hex\u662f72\uff0cl\u5bf9\u5e94\u7684\u5341\u516d\u8fdb\u5236\u6570\u662f6c\uff0cd\u5bf9\u5e94\u7684HEX\u662f64.<\/p>\n\n- \n
In the following code, what is going to be printed after 'y='<\/code>? (note: the answer is not a specific value.) Why does this happen?<\/p>\nprintf(\"x=%d y=%d\", 3);<\/code><\/pre>\n<\/li>\n<\/ol>\ny\u8f93\u51fa\u4e861\uff08\u6ca1\u6709\u5b9e\u9645\u610f\u4e49\uff09\uff0c\u539f\u56e0\u7b2c\u4e8c\u4e2a%d\u5728\u53c2\u6570\u5217\u8868\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u53c2\u6570\u4e0e\u4e4b\u5bf9\u5e94\u3002<\/p>\n
2 Backtrace (moderate)<\/h2>\n\n\u7f16\u5199\u4e00\u4e2a\u7a0b\u5e8f\uff0c\u8ffd\u8e2a\u51fd\u6570\u8c03\u7528\u8f68\u8ff9\u3002<\/p>\n
\u7a0b\u5e8f\u6808\uff1a<\/p>\n
.\n .\n +-> .\n | +-----------------+ |\n | | return address | |\n | | previous fp ------+\n | | saved registers |\n | | local variables |\n | | ... | <-+\n | +-----------------+ |\n | | return address | |\n +------ previous fp | |\n | saved registers | |\n | local variables | |\n +-> | ... | |\n | +-----------------+ |\n | | return address | |\n | | previous fp ------+\n | | saved registers |\n | | local variables |\n | | ... | <-+\n | +-----------------+ |\n | | return address | |\n +------ previous fp | |\n | saved registers | |\n | local variables | |\n $fp --> | ... | |\n +-----------------+ |\n | return address | |\n | previous fp ------+\n | saved registers |\n $sp --> | local variables |\n +-----------------+<\/code><\/pre>\n<\/blockquote>\n2.1 \u7406\u89e3\u8fd9\u4e2a\u7a0b\u5e8f\u6808<\/h3>\n
fp\u5bc4\u5b58\u5668\uff0c\u4fdd\u5b58\u7740\u5f53\u524d\u6808\u5e27\u7684\u8d77\u59cb\u4f4d\u7f6e\uff0csp\u5bc4\u5b58\u5668\uff0c\u4fdd\u5b58\u8fd9\u5f53\u524d\u4f60\u8fdb\u7a0b\u5f53\u524d\u7684\u6808\u6307\u9488\u3002\u6808\u5e27\u6307\u9488fp\u7684\u504f\u79fb(-8)\u7684\u4f4d\u7f6e\u5b58\u653e\u7684\u662f\u5f53\u524d\u6808\u5e27\u7684\u8fd4\u56de\u5730\u5740\uff0c\u504f\u79fb\uff08-16\uff09\u5b58\u653e\u7684\u662f\u4e0a\u4e00\u4e2a\u6808\u5e27\u7684\u8d77\u59cb\u4f4d\u7f6e\u3002\u5229\u7528\uff08-16\uff09\u7684\u504f\u79fb\u7684\u4f4d\u7f6e\u7684\u503c\uff0c\u5c31\u53ef\u4ee5\u8ffd\u8e2a\u5230\u4e0a\u4e00\u4e2a\u6808\u5e27\u3002<\/p>\n
2.2 \u5982\u4f55\u5224\u65ad\u8ffd\u8e2a\u7684\u7ec8\u70b9<\/h3>\n
\u5229\u7528hints\u91cc\u7684\u8fd9\u4e00\u6761\uff0c\u5185\u6838\u4e3a\u6bcf\u4e2a\u8fdb\u7a0b\u6808\u5206\u914d\u4e86\u4e00\u4e2a\u5bf9\u9f50\u7684\u9875\uff0c\u6240\u4ee5\u6240\u6709\u7684\u6808\u5e27\u90fd\u5e94\u8be5\u5728\u540c\u4e00\u4e2a\u6808\uff0c\u901a\u8fc7PGROUNDDOWN<\/code>\u5b8f\u5c31\u53ef\u4ee5\u77e5\u9053\u5f53\u524d\u6808\u5e27\u5730\u5740\u6240\u5728\u7684\u9875\u3002\u6bd4\u8f83\u5f53\u524d\u6808\u5e27\u548c\u4e0b\u4e00\u4e2a\u6808\u5e27\u7684\u5730\u5740\u6240\u5728\u7684\u9875\u9762\u7684\u8d77\u59cb\u4f4d\u7f6e\u662f\u4e0d\u662f\u76f8\u540c\uff0c\u5c31\u53ef\u4ee5\u5224\u65ad\u6808\u5e27\u8ffd\u8e2a\u662f\u4e0d\u662f\u8fbe\u5230\u4e86\u7ec8\u70b9\u3002<\/p>\n2.3 \u6839\u636ehints\u6dfb\u52a0\u76f8\u5e94\u7684\u51fd\u6570<\/h3>\n
\u8fd9\u4e00\u90e8\u5206\u770b\u770bhints\u8ddf\u7740\u505a\u5c31\u597d\u3002<\/p>\n
2.4 \u4ee3\u7801\u5b9e\u73b0<\/h3>\nvoid\nbacktrace(void) {\n printf("backtrace:\\n");\n\n uint64 fp = r_fp();\n\n while (1) {\n printf("%p\\n", *((uint64 *)(fp - 8)));\n uint64 prefp = *((uint64 *)(fp - 16));\n\n if (PGROUNDDOWN(fp) != PGROUNDDOWN(prefp)) {\n break;\n }\n\n fp = prefp;\n }\n}<\/code><\/pre>\n\u8981\u5904\u7406\u597d\u6574\u578b\u548c\u6307\u9488\u4e4b\u95f4\u7684\u533a\u522b<\/strong><\/p>\n\u6309\u7167\u9898\u76ee\u63cf\u8ff0\uff0c\u4e3a\u4e86\u65b9\u4fbf\u540e\u9762\u7684\u8c03\u8bd5\uff0c\u6211\u4eec\u53ef\u4ee5\u5c06\u8fd9\u4e2a\u5199\u597d\u7684\u51fd\u6570\uff0c\u5728panic<\/code>\u51fd\u6570\u4e2d\u8c03\u7528\uff0c\u4ee5\u8ffd\u8e2a\u9519\u8bef\u4fe1\u606f\u3002<\/p>\n3 Alarm (hard)<\/h2>\n\n\u5b9e\u73b0\u4e00\u4e2a\u7a0b\u5e8f\u8ba1\u65f6\u5668\uff0c\u5728\u4e00\u5b9a\u5468\u671f\u4e4b\u540e\u6267\u884c\u67d0\u4e00\u9879\u4efb\u52a1\u540e\u8fd4\u56de\u5f53\u524d\u7a0b\u5e8f\u3002<\/p>\n<\/blockquote>\n
3.1 \u90e8\u7f72sigalarm\u548csigreturn\u4e24\u4e2a\u7cfb\u7edf\u8c03\u7528<\/h3>\n
\u4eff\u7167lab syscall<\/code>\u4e2d\u58f0\u660e\u7cfb\u7edf\u8c03\u7528\u7684\u65b9\u6cd5\uff0c\u58f0\u660e\u8fd9\u4e24\u4e2a\u7cfb\u7edf\u8c03\u7528\u51fd\u6570\u3002<\/p>\n3.2 \u5206\u6790trap\u7684\u8fc7\u7a0b<\/h3>\n\n- \u7528\u6237\u63d0\u51fa\u7cfb\u7edf\u8c03\u7528\uff0c\u5e76\u63d0\u4f9b\u7cfb\u7edf\u8c03\u7528\u53f7\u3002<\/li>\n
- \u6c47\u7f16\u8c03\u7528
ecall<\/code>\u8fdb\u5165\u5185\u6838\u6001\u3002<\/li>\n- \u8fdb\u5165
usertrap<\/code>\u51fd\u6570\u3002<\/li>\n- \u5982\u679c\u662f\u7528\u6237\u63d0\u51fa\u7684\u7cfb\u7edf\u8c03\u7528\u4e2d\u65ad\uff0c\u5219\u8fdb\u5165\u76f8\u5e94\u7684syscall\u51fd\u6570\uff0c\u7528\u6237\u8fd4\u56de\u7684\u5730\u5740\u4e3a\u8fdb\u5165\u5730\u5740\u52a04\u3002<\/li>\n
- \u5982\u679c\u662f\u65f6\u949f\u5468\u671f\u4e2d\u65ad\uff0c\u5219\u5360\u65f6\u8df3\u8fc7\uff0c\u5e76\u4e0d\u4f7f\u7528CPU\u7684\u8d44\u6e90\u3002<\/li>\n
- \u4e2d\u65ad\u5904\u7406\u5b8c\u4e4b\u540e\uff0c\u56de\u5230\u7528\u6237\u6001\u3002<\/li>\n<\/ol>\n
3.3 sigalarm<\/h3>\n
sigalarm\u8bf7\u6c42\u5728\u4e00\u5b9a\u6570\u91cf\u7684\u65f6\u949f\u4e2d\u65ad\u4e4b\u540e\u6267\u884c\u7528\u6237\u63d0\u4f9b\u7684\u4ee3\u7801\uff0c\u800c\u4e0d\u662f\u4ece\u4e2d\u65ad\u5730\u5740\u7ee7\u7eed\u6267\u884c\u3002\u5c40\u90e8\u53d8\u91cfwhich_dev<\/code>\u8868\u793a\u8be5\u8c03\u7528\u7684\u7c7b\u578b\uff0c\u5982\u679c\u503c\u4e3a2\uff0c\u5219\u8be5\u4e2d\u65ad\u7c7b\u578b\u662f\u65f6\u949f\u5468\u671f\u7684\u4e2d\u65ad\u3002\u5982\u679c\u662f\u65f6\u949f\u5468\u671f\u7684\u4e2d\u65ad\uff0c\u6211\u4e48\u600e\u4e48\u77e5\u9053\u8fc7\u4e86\u591a\u5c11\u4e2a\u65f6\u949f\u5468\u671f\uff0c\u4ee5\u53ca\u7528\u6237\u8981\u6c42\u7684\u591a\u5c11\u65f6\u949f\u5468\u671f\u8fc7\u540e\u6267\u884c\u7528\u6237\u4ee3\u7801\uff0c\u4ee5\u53ca\u7528\u6237\u4ee3\u7801\u5730\u5740\u5462\u3002\u4e3a\u4e86\u50a8\u5b58\u8fd9\u4e9b\u4fe1\u606f\uff0c\u6211\u4eec\u5728\u8fdb\u7a0b\u7ed3\u6784\u4f53struct proc<\/code>\u4e2d\u8bbe\u7f6e\u8fd9\u4e9b\u4fe1\u606f\u3002<\/p>\nint alarm_interval;\nvoid (*user_handler)();\nint ticks_pass;<\/code><\/pre>\n\u8c03\u7528syscall<\/code>\u7684\u65f6\u5019\uff0c\u6211\u4eec\u4ece\u7528\u6237\u6001\u83b7\u5f97\u5468\u671f\u95f4\u9694\u6570\uff0c\u548c\u7528\u6237\u4ee3\u7801\u5730\u5740\u3002<\/p>\nuint64\nsys_sigalarm(void)\n{\n int interval;\n uint64 uhandler;\n\n argint(0, &interval);\n argaddr(1, &uhandler);\n\n struct proc *p = myproc();\n\n p->alarm_interval = interval;\n p->user_handler = (void (*)())uhandler;\n p->ticks_pass = 0;\n\n return 0;\n}<\/code><\/pre>\n\u5f53usertrap<\/code>\u51fd\u6570\u83b7\u5f97\u4e86\u65f6\u949f\u4e2d\u65ad\u4e4b\u540e\uff0c\u5982\u679c\u8be5\u8fdb\u7a0b\u6709\u4e2d\u65ad\u95f4\u9694\u8981\u6c42\uff0c\u5219\u5728tickspass\u4e0a\u52a0\u4e00\uff0c\u5982\u679ctickspass\u6570\u7b49\u4e8e\u4e2d\u65ad\u95f4\u9694\u8981\u6c42\uff0c\u5219\u5c06p->trapframe<\/code>\u57df\u4e2d\u7684epc<\/code>\uff08\u8868\u793a\u8fd4\u56de\u7528\u6237\u6001\u7684\u7a0b\u5e8f\u8ba1\u6570\u5668\uff09\u8bbe\u7f6e\u4e3a\u7528\u6237\u8981\u6c42\u7684\u4ee3\u7801\u5730\u5740\uff0c\u8fd9\u4e2a\u5730\u5740\u53ef\u80fd\u4e3a0\uff0c\u6240\u4ee5\u6211\u4eec\u4e0d\u80fd\u4f7f\u7528\u7528\u6237\u4ee3\u7801\u5730\u5740\u6765\u5224\u65ad\u7528\u6237\u662f\u5426\u6709\u5468\u671f\u4efb\u52a1\u8bf7\u6c42<\/strong>\uff0c\u7136\u540e\u5c06tickspass\u7f6e\u4e3a0\uff0c\u91cd\u65b0\u5f00\u59cb\u8ba1\u6570\u3002<\/p>\n\u8fd9\u6837\u5b9e\u73b0\u540e\u53ef\u4ee5\u901a\u8fc7\u8be5\u4efb\u52a1\u7684\u6d4b\u8bd50\u3002<\/p>\n
if (p->alarm_interval) {\n p->ticks_pass++;\n if (p->ticks_pass == p->alarm_interval) {\n p->ticks_pass = 0;\n p->trapframe->epc = (uint64)p->user_handler;\n }\n}<\/code><\/pre>\n3.4 \u5904\u7406sigalarm\u7528\u6237\u6001\u7ed3\u675f\u6062\u590d\u8fdb\u7a0b<\/h3>\n\n\u9898\u76ee\u63d0\u4f9b\u4e86\u4e00\u79cd\u601d\u8def\uff0c\u8fdb\u5165\u5230\u7528\u6237\u4ee3\u7801\uff0c\u5e76\u5c06\u7528\u6237\u4ee3\u7801\u8fd0\u884c\u7ed3\u675f\u4e4b\u540e\u5fc5\u987b\u8c03\u7528sigreturn<\/code>\u7cfb\u7edf\u8c03\u7528\u3002\u6211\u4eec\u53ef\u4ee5\u5728sigreturn<\/code>\u5904\u7406\u6062\u590d\u7528\u6237\u8fdb\u7a0b\u3002<\/p>\ntrapframe\u4fdd\u5b58\u8fdb\u5165\u5185\u6838\u6001\u540e\u7684\u7528\u6237\u6001\u7684\u5bc4\u5b58\u5668\u4fe1\u606f\u3002<\/p>\n<\/blockquote>\n
3.4.1 \u9700\u8981\u4fdd\u5b58\u7684\u5bc4\u5b58\u5668<\/h4>\n
![\"image-20221101150634287\"](\"data:image\/svg+xml;base64,PCEtLUFyZ29uTG9hZGluZy0tPgo8c3ZnIHdpZHRoPSIxIiBoZWlnaHQ9IjEiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgc3Ryb2tlPSIjZmZmZmZmMDAiPjxnPjwvZz4KPC9zdmc+\")
<\/div><\/p>\n\u4eceRISC-V ISA<\/code>\u53c2\u8003\u6587\u6863\u4e2d\u5f97\u5230\uff0c\u9664\u4e86t0, t1, t2, ... , t6<\/code>\u662f\u5360\u65f6\u5bc4\u5b58\u5668\u5916\uff0c\u5176\u4ed6\u5bc4\u5b58\u5668\u90fd\u6709\u5b9e\u9645\u7684\u7528\u9014\uff08\u7b14\u8005\u4fdd\u9669\u8d77\u89c1\uff0c\u90fd\u628a\u8fd9\u4e9b\u5bc4\u5b58\u5668\u7684\u4fe1\u606f\u90fd\u53e6\u5b58\u8d77\u6765\u4e86\uff09\uff0c\u800c\u4e14\u8fdb\u7a0b\u7ed3\u6784\u4f53\u4e2d\u6709context<\/code>\u53d8\u91cf\uff0c\u4fdd\u5b58\u7684\u662f\u8be5\u8fdb\u7a0b\u88ab\u6682\u505c\u4e4b\u540e\u7684\u5bc4\u5b58\u5668\u4fe1\u606f\uff0c\u4ee5\u4fbf\u4e4b\u540e\u91cd\u65b0\u8fd0\u884c\u4e4b\u540e\u91cd\u65b0\u6062\u590d\u8fdb\u7a0b\u72b6\u6001\u3002\u53ef\u4ee5\u6a21\u4eff\uff0c\u8bbe\u7f6e\u4e00\u4e2ausercontext<\/code>\u53d8\u91cf\uff0c\u6765\u4fdd\u5b58\u8c03\u7528\u7528\u6237\u4ee3\u7801\u4e4b\u524d\uff0c\u4fdd\u5b58\u5728\u6b64\u4e4b\u524d\u7528\u6237\u6001\u5bc4\u5b58\u5668\u7684\u72b6\u6001\u3002<\/p>\nstruct usercontext {\n uint64 ra;\n uint64 sp;\n uint64 gp;\n uint64 tp;\n uint64 epc;\n\n \/* 96 *\/ uint64 s0;\n \/* 104 *\/ uint64 s1;\n \/* 112 *\/ uint64 a0;\n \/* 120 *\/ uint64 a1;\n \/* 128 *\/ uint64 a2;\n \/* 136 *\/ uint64 a3;\n \/* 144 *\/ uint64 a4;\n \/* 152 *\/ uint64 a5;\n \/* 160 *\/ uint64 a6;\n \/* 168 *\/ uint64 a7;\n \/* 176 *\/ uint64 s2;\n \/* 184 *\/ uint64 s3;\n \/* 192 *\/ uint64 s4;\n \/* 200 *\/ uint64 s5;\n \/* 208 *\/ uint64 s6;\n \/* 216 *\/ uint64 s7;\n \/* 224 *\/ uint64 s8;\n \/* 232 *\/ uint64 s9;\n \/* 240 *\/ uint64 s10;\n \/* 248 *\/ uint64 s11;\n};<\/code><\/pre>\n3.4.2 \u4fdd\u5b58\u5bc4\u5b58\u5668\u72b6\u6001<\/h4>\n
\u5f53\u65f6\u949f\u4e2d\u65ad\u6570\u8fbe\u5230\u4e86\u7528\u6237\u63d0\u51fa\u8981\u6c42\u7684\u4e2d\u65ad\u6570\u4e4b\u540e\uff0c\u5728\u8c03\u7528\u7528\u6237\u8fdb\u7a0b\u4ee3\u7801\u4e4b\u524d\uff0c\u6211\u4eec\u4fdd\u5b58\u5bc4\u5b58\u5668\u4fe1\u606f\uff0c\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n
if (which_dev == 2) {\n if (p->alarm_interval) {\n p->ticks_pass++;\n if (p->ticks_pass == p->alarm_interval) {\n\n p->usercontext.epc = p->trapframe->epc;\n p->usercontext.ra = p->trapframe->ra;\n p->usercontext.sp = p->trapframe->sp;\n p->usercontext.gp = p->trapframe->gp;\n p->usercontext.tp = p->trapframe->tp;\n p->usercontext.s0 = p->trapframe->s0;\n p->usercontext.s1 = p->trapframe->s1;\n p->usercontext.a0 = p->trapframe->a0;\n p->usercontext.a1 = p->trapframe->a1;\n p->usercontext.a2 = p->trapframe->a2;\n p->usercontext.a3 = p->trapframe->a3;\n p->usercontext.a4 = p->trapframe->a4;\n p->usercontext.a5 = p->trapframe->a5;\n p->usercontext.a6 = p->trapframe->a6;\n p->usercontext.a7 = p->trapframe->a7;\n p->usercontext.s2 = p->trapframe->s2;\n p->usercontext.s3 = p->trapframe->s3;\n p->usercontext.s4 = p->trapframe->s4;\n p->usercontext.s5 = p->trapframe->s5;\n p->usercontext.s6 = p->trapframe->s6;\n p->usercontext.s7 = p->trapframe->s7;\n p->usercontext.s8 = p->trapframe->s8;\n p->usercontext.s9 = p->trapframe->s9;\n p->usercontext.s10 = p->trapframe->s10;\n p->usercontext.s11 = p->trapframe->s11;\n\n p->ticks_pass = 0;\n p->trapframe->epc = (uint64)p->user_handler;\n }\n }\n}<\/code><\/pre>\n3.4.3 \u6062\u590d\u5bc4\u5b58\u5668\u72b6\u6001<\/h4>\n
\u6267\u884c\u5b8c\u7528\u6237\u6001\u7684\u4ee3\u7801\u4e4b\u540e\uff0c\u4f1a\u8c03\u7528\u7cfb\u7edf\u51fd\u6570sigreturn<\/code>\uff0c\u8fdb\u5165\u8be5\u51fd\u6570\u540e\uff0c\u6211\u4eec\u6062\u590d\u5bc4\u5b58\u5668\u3002\u4e4b\u540e\u4f1a\u5728usertrap<\/code>\u51fd\u6570\u8fd4\u56de\u5230\u7528\u6237\u6001\u3002<\/p>\nuint64\nsys_sigreturn()\n{\n struct proc *p = myproc();\n\n p->trapframe->ra = p->usercontext.ra;\n p->trapframe->sp = p->usercontext.sp;\n p->trapframe->gp = p->usercontext.gp;\n p->trapframe->tp = p->usercontext.tp;\n p->trapframe->s0 = p->usercontext.s0;\n p->trapframe->s1 = p->usercontext.s1;\n p->trapframe->a0 = p->usercontext.a0;\n p->trapframe->a1 = p->usercontext.a1;\n p->trapframe->a2 = p->usercontext.a2;\n p->trapframe->a3 = p->usercontext.a3;\n p->trapframe->a4 = p->usercontext.a4;\n p->trapframe->a5 = p->usercontext.a5;\n p->trapframe->a6 = p->usercontext.a6;\n p->trapframe->a7 = p->usercontext.a7;\n p->trapframe->s2 = p->usercontext.s2;\n p->trapframe->s3 = p->usercontext.s3;\n p->trapframe->s4 = p->usercontext.s4;\n p->trapframe->s5 = p->usercontext.s5;\n p->trapframe->s6 = p->usercontext.s6;\n p->trapframe->s7 = p->usercontext.s7;\n p->trapframe->s8 = p->usercontext.s8;\n p->trapframe->s9 = p->usercontext.s9;\n p->trapframe->s10 = p->usercontext.s10;\n p->trapframe->s11 = p->usercontext.s11;\n p->trapframe->epc = p->usercontext.epc;\n\n return 0;\n}<\/code><\/pre>\n\u6b64\u65f6\u6d4b\u8bd5\uff0c\u5c31\u4f1a\u901a\u8fc7\u6d4b\u8bd51\u3002<\/p>\n
3.4.4 \u907f\u514d\u91cd\u590d\u8c03\u7528<\/h4>\n
\u5b58\u5728\u4e0b\u5217\u60c5\u51b5\uff0c\u7528\u6237\u8bf7\u6c42\u6bcf\u96942\u4e2a\u65f6\u949f\u5468\u671f\u8c03\u7528\u5904\u7406\u7a0b\u5e8f\uff0c\u800c\u5904\u7406\u7a0b\u5e8f\u9700\u8981\u4e09\u4e2a\u65f6\u949f\u5468\u671f\uff0c\u6b64\u65f6\u5b58\u5728\u7cfb\u7edf\u8c03\u7528\u6ca1\u6709\u7ed3\u675f\u7684\u60c5\u51b5\u4e0b\uff0c\u53c8\u4e00\u6b21\u8c03\u7528\u4e86\u7528\u6237\u7a0b\u5e8f\uff0c\u5b58\u5728\u91cd\u590d\u8c03\u7528\u7684\u60c5\u51b5\u3002<\/p>\n
\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u60c5\u51b5\uff0c\u6211\u4eec\u5728\u8fdb\u7a0b\u7ed3\u6784\u4f53\u4e2d\u589e\u52a0\u4e00\u4e2a\u53d8\u91cf\uff0c\u8868\u793a\u662f\u5426\u6b63\u5728\u6267\u884c\u7528\u6237\u4ee3\u7801\u8c03\u7528\u3002\u4e0d\u59a8\u8bbe\u8be5\u53d8\u91cf\u4e3aalarmstatus<\/code>\u3002\u5f53\u65f6\u949f\u5468\u671f\u6570\u8fbe\u5230\u7528\u6237\u8981\u6c42\u7684\u5468\u671f\u6570\u4e4b\u540e\uff0c\u6211\u4eec\u8bbe\u7f6e\u8fd9\u4e2a\u6807\u8bb0\u4f4d\uff0c\u5f53\u7528\u6237\u8c03\u7528\u4e86sigreturn<\/code>\u51fd\u6570\u65f6\uff0c\u6211\u4eec\u5c06\u8be5\u53d8\u91cf\u8bbe\u7f6e\u4e3a0\u3002<\/p>\n\u5f53\u8be5\u53d8\u91cf\u503c\u4e3a0\u7684\u65f6\u5019\uff0c\u6211\u4eec\u624d\u53ef\u4ee5\u8fdb\u5165\u7528\u6237\u7684\u4ee3\u7801\uff0c\u5426\u5219\uff0c\u8df3\u8fc7\u8fd9\u4e2a\u5468\u671f\u3002<\/p>\n
------trap,c: usertrap--------\nif (.... && p->alarmstatus == 0) {\n ...\n p->alarmstatus = 1;\n}\n\n------syscall.c\/sys_sigreturn-------\nvoid\n sys_sigreturn()\n{\n ...\n p->alarmstatus = 0;\n}<\/code><\/pre>\n\u6b64\u65f6\uff0c\u901a\u8fc7\u6d4b\u8bd52\u3002<\/p>\n
3.4.5 \u4fdd\u62a4a0\u5bc4\u5b58\u5668<\/h4>\n
a0\u5bc4\u5b58\u5668\u4f5c\u4e3a\u51fd\u6570\u8fd4\u56de\u503c\u6240\u4f7f\u7528\u7684\u5bc4\u5b58\u5668\uff0c\u5728\u8c03\u7528syscall\u7684\u65f6\u5019\uff0csyscall\u7684\u8fd4\u56de\u503c\u5c31\u4f1a\u8986\u76d6\u5230a0\u5bc4\u5b58\u5668\uff0c\u5bfc\u81f4\u4e4b\u524d\u7528\u6237\u6001\u7684a0\u5bc4\u5b58\u5668\u7684\u503c\u88ab\u7834\u574f\u3002\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u6211\u4eec\u53ef\u4ee5\u5c06\u7528\u6237\u6001\u4e4b\u524d\u7684a0\u503c\u4f5c\u4e3asigreturn<\/code>\u7684\u8fd4\u56de\u503c\u3002<\/p>\n\u6b64\u65f6\u6574\u4e2asigreturn<\/code>\u7684\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\nuint64\nsys_sigreturn()\n{\n struct proc *p = myproc();\n\n p->trapframe->ra = p->usercontext.ra;\n p->trapframe->sp = p->usercontext.sp;\n p->trapframe->gp = p->usercontext.gp;\n p->trapframe->tp = p->usercontext.tp;\n p->trapframe->s0 = p->usercontext.s0;\n p->trapframe->s1 = p->usercontext.s1;\n p->trapframe->a0 = p->usercontext.a0;\n p->trapframe->a1 = p->usercontext.a1;\n p->trapframe->a2 = p->usercontext.a2;\n p->trapframe->a3 = p->usercontext.a3;\n p->trapframe->a4 = p->usercontext.a4;\n p->trapframe->a5 = p->usercontext.a5;\n p->trapframe->a6 = p->usercontext.a6;\n p->trapframe->a7 = p->usercontext.a7;\n p->trapframe->s2 = p->usercontext.s2;\n p->trapframe->s3 = p->usercontext.s3;\n p->trapframe->s4 = p->usercontext.s4;\n p->trapframe->s5 = p->usercontext.s5;\n p->trapframe->s6 = p->usercontext.s6;\n p->trapframe->s7 = p->usercontext.s7;\n p->trapframe->s8 = p->usercontext.s8;\n p->trapframe->s9 = p->usercontext.s9;\n p->trapframe->s10 = p->usercontext.s10;\n p->trapframe->s11 = p->usercontext.s11;\n p->trapframe->epc = p->usercontext.epc;\n\n p->alarmstatus = 0;\n\n return p->usercontext.a0;\n}<\/code><\/pre>\n\u6b64\u65f6\u6d4b\u8bd5\uff0c\u901a\u8fc7\u4e86\u6240\u6709\u6d4b\u8bd5\u3002<\/p>\n
3.5 \u8003\u8651\u5bf9\u58f0\u660e\u7684\u53d8\u91cf\u7684\u5206\u914d\u548c\u91ca\u653e<\/h3>\n
\u5728\u8fd9\u4e2a\u5b9e\u9a8c\u4e2d\uff0c\u6211\u4eec\u5b9a\u4e49\u4e86alarm_interval<\/code>\/userhandler<\/code>\/usercontext<\/code>\/alarmstatus<\/code>\/ticks_pass<\/code>\uff0c\u8fdb\u7a0b\u521b\u5efa\u521d\u671f\u8981\u5168\u90e8\u7f6e0\uff0c\u8fdb\u7a0b\u7ed3\u675f\u4e5f\u5168\u90e8\u5f52\u96f6\u3002<\/p>\n---allocproc---\n{\n ....\n memset(&p->usercontext, 0, sizeof(p->usercontext));\n p->alarm_interval = 0;\n p->user_handler = 0;\n p->ticks_pass = 0;\n p->alarmstatus = 0;\n ....\n}\n\n---freeproc---\n{\n ....\n p->alarm_interval = 0;\n p->user_handler = 0;\n p->ticks_pass = 0;\n p->alarmstatus = 0;\n ....\n}<\/code><\/pre>\n4 END<\/h2>\n
\u5b9e\u9a8c\u5b8c\u6210\uff0c\u6d4b\u8bd5\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n
== Test answers-traps.txt == answers-traps.txt: OK \n== Test backtrace test == \n$ make qemu-gdb\nbacktrace test: OK (4.0s) \n== Test running alarmtest == \n$ make qemu-gdb\n(6.2s) \n== Test alarmtest: test0 == \n alarmtest: test0: OK \n== Test alarmtest: test1 == \n alarmtest: test1: OK \n== Test alarmtest: test2 == \n alarmtest: test2: OK \n== Test alarmtest: test3 == \n alarmtest: test3: OK \n== Test usertests == \n$ make qemu-gdb\nusertests: OK (204.3s) \n== Test time == \ntime: OK \nScore: 95\/95<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"xv6\u64cd\u4f5c\u7cfb\u7edf\u5b9e\u9a8c4\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[14],"class_list":["post-52","post","type-post","status-publish","format-standard","hentry","category-os","tag-xv6"],"_links":{"self":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts\/52","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/comments?post=52"}],"version-history":[{"count":0,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts\/52\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/media?parent=52"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/categories?post=52"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/tags?post=52"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\u9605\u8bfb \u6839\u636e Run the following code.<\/p>\n What is the output? <\/p>\n<\/li>\n<\/ol>\n HE110 World\uff0c 57616\u7684\u5341\u516d\u8fdb\u5236\u6570\u503c In the following code, what is going to be printed after y\u8f93\u51fa\u4e861\uff08\u6ca1\u6709\u5b9e\u9645\u610f\u4e49\uff09\uff0c\u539f\u56e0\u7b2c\u4e8c\u4e2a%d\u5728\u53c2\u6570\u5217\u8868\u4e2d\u6ca1\u6709\u5bf9\u5e94\u7684\u53c2\u6570\u4e0e\u4e4b\u5bf9\u5e94\u3002<\/p>\n \u7f16\u5199\u4e00\u4e2a\u7a0b\u5e8f\uff0c\u8ffd\u8e2a\u51fd\u6570\u8c03\u7528\u8f68\u8ff9\u3002<\/p>\n \u7a0b\u5e8f\u6808\uff1a<\/p>\n fp\u5bc4\u5b58\u5668\uff0c\u4fdd\u5b58\u7740\u5f53\u524d\u6808\u5e27\u7684\u8d77\u59cb\u4f4d\u7f6e\uff0csp\u5bc4\u5b58\u5668\uff0c\u4fdd\u5b58\u8fd9\u5f53\u524d\u4f60\u8fdb\u7a0b\u5f53\u524d\u7684\u6808\u6307\u9488\u3002\u6808\u5e27\u6307\u9488fp\u7684\u504f\u79fb(-8)\u7684\u4f4d\u7f6e\u5b58\u653e\u7684\u662f\u5f53\u524d\u6808\u5e27\u7684\u8fd4\u56de\u5730\u5740\uff0c\u504f\u79fb\uff08-16\uff09\u5b58\u653e\u7684\u662f\u4e0a\u4e00\u4e2a\u6808\u5e27\u7684\u8d77\u59cb\u4f4d\u7f6e\u3002\u5229\u7528\uff08-16\uff09\u7684\u504f\u79fb\u7684\u4f4d\u7f6e\u7684\u503c\uff0c\u5c31\u53ef\u4ee5\u8ffd\u8e2a\u5230\u4e0a\u4e00\u4e2a\u6808\u5e27\u3002<\/p>\n \u5229\u7528hints\u91cc\u7684\u8fd9\u4e00\u6761\uff0c\u5185\u6838\u4e3a\u6bcf\u4e2a\u8fdb\u7a0b\u6808\u5206\u914d\u4e86\u4e00\u4e2a\u5bf9\u9f50\u7684\u9875\uff0c\u6240\u4ee5\u6240\u6709\u7684\u6808\u5e27\u90fd\u5e94\u8be5\u5728\u540c\u4e00\u4e2a\u6808\uff0c\u901a\u8fc7 \u8fd9\u4e00\u90e8\u5206\u770b\u770bhints\u8ddf\u7740\u505a\u5c31\u597d\u3002<\/p>\n \u8981\u5904\u7406\u597d\u6574\u578b\u548c\u6307\u9488\u4e4b\u95f4\u7684\u533a\u522b<\/strong><\/p>\n \u6309\u7167\u9898\u76ee\u63cf\u8ff0\uff0c\u4e3a\u4e86\u65b9\u4fbf\u540e\u9762\u7684\u8c03\u8bd5\uff0c\u6211\u4eec\u53ef\u4ee5\u5c06\u8fd9\u4e2a\u5199\u597d\u7684\u51fd\u6570\uff0c\u5728 \u5b9e\u73b0\u4e00\u4e2a\u7a0b\u5e8f\u8ba1\u65f6\u5668\uff0c\u5728\u4e00\u5b9a\u5468\u671f\u4e4b\u540e\u6267\u884c\u67d0\u4e00\u9879\u4efb\u52a1\u540e\u8fd4\u56de\u5f53\u524d\u7a0b\u5e8f\u3002<\/p>\n<\/blockquote>\n \u4eff\u7167 sigalarm\u8bf7\u6c42\u5728\u4e00\u5b9a\u6570\u91cf\u7684\u65f6\u949f\u4e2d\u65ad\u4e4b\u540e\u6267\u884c\u7528\u6237\u63d0\u4f9b\u7684\u4ee3\u7801\uff0c\u800c\u4e0d\u662f\u4ece\u4e2d\u65ad\u5730\u5740\u7ee7\u7eed\u6267\u884c\u3002\u5c40\u90e8\u53d8\u91cf \u8c03\u7528 \u5f53 \u8fd9\u6837\u5b9e\u73b0\u540e\u53ef\u4ee5\u901a\u8fc7\u8be5\u4efb\u52a1\u7684\u6d4b\u8bd50\u3002<\/p>\n \u9898\u76ee\u63d0\u4f9b\u4e86\u4e00\u79cd\u601d\u8def\uff0c\u8fdb\u5165\u5230\u7528\u6237\u4ee3\u7801\uff0c\u5e76\u5c06\u7528\u6237\u4ee3\u7801\u8fd0\u884c\u7ed3\u675f\u4e4b\u540e\u5fc5\u987b\u8c03\u7528 trapframe\u4fdd\u5b58\u8fdb\u5165\u5185\u6838\u6001\u540e\u7684\u7528\u6237\u6001\u7684\u5bc4\u5b58\u5668\u4fe1\u606f\u3002<\/p>\n<\/blockquote>\n \u4ece \u5f53\u65f6\u949f\u4e2d\u65ad\u6570\u8fbe\u5230\u4e86\u7528\u6237\u63d0\u51fa\u8981\u6c42\u7684\u4e2d\u65ad\u6570\u4e4b\u540e\uff0c\u5728\u8c03\u7528\u7528\u6237\u8fdb\u7a0b\u4ee3\u7801\u4e4b\u524d\uff0c\u6211\u4eec\u4fdd\u5b58\u5bc4\u5b58\u5668\u4fe1\u606f\uff0c\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n \u6267\u884c\u5b8c\u7528\u6237\u6001\u7684\u4ee3\u7801\u4e4b\u540e\uff0c\u4f1a\u8c03\u7528\u7cfb\u7edf\u51fd\u6570 \u6b64\u65f6\u6d4b\u8bd5\uff0c\u5c31\u4f1a\u901a\u8fc7\u6d4b\u8bd51\u3002<\/p>\n \u5b58\u5728\u4e0b\u5217\u60c5\u51b5\uff0c\u7528\u6237\u8bf7\u6c42\u6bcf\u96942\u4e2a\u65f6\u949f\u5468\u671f\u8c03\u7528\u5904\u7406\u7a0b\u5e8f\uff0c\u800c\u5904\u7406\u7a0b\u5e8f\u9700\u8981\u4e09\u4e2a\u65f6\u949f\u5468\u671f\uff0c\u6b64\u65f6\u5b58\u5728\u7cfb\u7edf\u8c03\u7528\u6ca1\u6709\u7ed3\u675f\u7684\u60c5\u51b5\u4e0b\uff0c\u53c8\u4e00\u6b21\u8c03\u7528\u4e86\u7528\u6237\u7a0b\u5e8f\uff0c\u5b58\u5728\u91cd\u590d\u8c03\u7528\u7684\u60c5\u51b5\u3002<\/p>\n \u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u60c5\u51b5\uff0c\u6211\u4eec\u5728\u8fdb\u7a0b\u7ed3\u6784\u4f53\u4e2d\u589e\u52a0\u4e00\u4e2a\u53d8\u91cf\uff0c\u8868\u793a\u662f\u5426\u6b63\u5728\u6267\u884c\u7528\u6237\u4ee3\u7801\u8c03\u7528\u3002\u4e0d\u59a8\u8bbe\u8be5\u53d8\u91cf\u4e3a \u5f53\u8be5\u53d8\u91cf\u503c\u4e3a0\u7684\u65f6\u5019\uff0c\u6211\u4eec\u624d\u53ef\u4ee5\u8fdb\u5165\u7528\u6237\u7684\u4ee3\u7801\uff0c\u5426\u5219\uff0c\u8df3\u8fc7\u8fd9\u4e2a\u5468\u671f\u3002<\/p>\n \u6b64\u65f6\uff0c\u901a\u8fc7\u6d4b\u8bd52\u3002<\/p>\n a0\u5bc4\u5b58\u5668\u4f5c\u4e3a\u51fd\u6570\u8fd4\u56de\u503c\u6240\u4f7f\u7528\u7684\u5bc4\u5b58\u5668\uff0c\u5728\u8c03\u7528syscall\u7684\u65f6\u5019\uff0csyscall\u7684\u8fd4\u56de\u503c\u5c31\u4f1a\u8986\u76d6\u5230a0\u5bc4\u5b58\u5668\uff0c\u5bfc\u81f4\u4e4b\u524d\u7528\u6237\u6001\u7684a0\u5bc4\u5b58\u5668\u7684\u503c\u88ab\u7834\u574f\u3002\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee\u9898\uff0c\u6211\u4eec\u53ef\u4ee5\u5c06\u7528\u6237\u6001\u4e4b\u524d\u7684a0\u503c\u4f5c\u4e3a \u6b64\u65f6\u6574\u4e2a \u6b64\u65f6\u6d4b\u8bd5\uff0c\u901a\u8fc7\u4e86\u6240\u6709\u6d4b\u8bd5\u3002<\/p>\n \u5728\u8fd9\u4e2a\u5b9e\u9a8c\u4e2d\uff0c\u6211\u4eec\u5b9a\u4e49\u4e86 \u5b9e\u9a8c\u5b8c\u6210\uff0c\u6d4b\u8bd5\u7ed3\u679c\u5982\u4e0b\uff1a<\/p>\n xv6\u64cd\u4f5c\u7cfb\u7edf\u5b9e\u9a8c4\u3002<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[14],"class_list":["post-52","post","type-post","status-publish","format-standard","hentry","category-os","tag-xv6"],"_links":{"self":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts\/52","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/comments?post=52"}],"version-history":[{"count":0,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/posts\/52\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/media?parent=52"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/categories?post=52"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.yewpo.top\/index.php\/wp-json\/wp\/v2\/tags?post=52"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}user\/call.asm<\/code>\uff0c\u56de\u7b54\u4e0b\u5217\u95ee\u9898\u3002<\/p>\n<\/blockquote>\n\n
printf<\/code>?<\/li>\n<\/ol>\nmain<\/code>\u51fd\u6570\u8c03\u7528printf<\/code>\u51fd\u6570\u65f6\u5c31\u5c06\u4e09\u4e2a\u53c2\u6570\u4fdd\u5b58\u5728\u4e86a0, a1, a2<\/code>\u4e2d\uff0c\u5176\u4e2d13\uff08\u7b2c3\u4e2a\u53c2\u6570\uff09\u4fdd\u5b58\u5728\u4e86a2<\/code>\u5bc4\u5b58\u5668\u4e2d\u3002<\/p>\nvoid main(void) {\n 1c: 1141 addi sp,sp,-16\n 1e: e406 sd ra,8(sp)\n 20: e022 sd s0,0(sp)\n 22: 0800 addi s0,sp,16\n printf("%d %d\\n", f(8)+1, 13);\n 24: 4635 li a2,13\n 26: 45b1 li a1,12\n 28: 00000517 auipc a0,0x0\n 2c: 7c850513 addi a0,a0,1992 # 7f0 <malloc+0xe8>\n 30: 00000097 auipc ra,0x0\n 34: 61a080e7 jalr 1562(ra) # 64a <printf>\n exit(0);\n 38: 4501 li a0,0\n 3a: 00000097 auipc ra,0x0\n 3e: 298080e7 jalr 664(ra) # 2d2 <exit><\/code><\/pre>\n\n
f<\/code> in the assembly code for main? Where is the call to g<\/code>? (Hint: the compiler may inline functions.)<\/li>\n<\/ol>\nmain<\/code>\u4e2d\u5728\u8c03\u7528printf<\/code>\u51fd\u6570\u7684\u65f6\u5019\uff0c\u4f20\u9012\u53c2\u6570\u65f6\u8c03\u7528\u4e86f<\/code>\u51fd\u6570\uff0c\u540c\u65f6f<\/code>\u51fd\u6570\u5728\u8fd4\u56de\u7684\u65f6\u5019\u8c03\u7528\u4e86g<\/code>\u51fd\u6570\u3002<\/p>\nint f(int x) {\n e: 1141 addi sp,sp,-16\n 10: e422 sd s0,8(sp)\n 12: 0800 addi s0,sp,16\n return g(x);\n}<\/code><\/pre>\n\n
printf<\/code> located?<\/li>\n<\/ol>\n000000000000064a <printf>:<\/code><\/p>\n\n
ra<\/code> just after the jalr<\/code> to printf<\/code> in main<\/code>?<\/li>\n<\/ol>\nRISC-V ISA<\/code>\u7684jalr<\/code>\u6307\u4ee4\u7684\u4f5c\u7528\uff0c\u4f1a\u5c06\u4e0b\u4e00\u6761\u6307\u4ee4\u7684\u5730\u5740\u4fdd\u5b58\u5728\u5bc4\u5b58\u5668ra<\/code>\u91cc\uff0c\u6240\u4ee5ra<\/code>\u7684\u503c\u662f0x38<\/code>\u3002<\/p>\n\n
unsigned int i = 0x00646c72;\nprintf(\"H%x Wo%s\", 57616, &i);\n<\/code><\/pre>\n0xE110<\/code>\uff0cr\u5bf9\u5e94\u7684hex\u662f72\uff0cl\u5bf9\u5e94\u7684\u5341\u516d\u8fdb\u5236\u6570\u662f6c\uff0cd\u5bf9\u5e94\u7684HEX\u662f64.<\/p>\n\n
'y='<\/code>? (note: the answer is not a specific value.) Why does this happen?<\/p>\nprintf(\"x=%d y=%d\", 3);<\/code><\/pre>\n<\/li>\n<\/ol>\n2 Backtrace (moderate)<\/h2>\n
\n
.\n .\n +-> .\n | +-----------------+ |\n | | return address | |\n | | previous fp ------+\n | | saved registers |\n | | local variables |\n | | ... | <-+\n | +-----------------+ |\n | | return address | |\n +------ previous fp | |\n | saved registers | |\n | local variables | |\n +-> | ... | |\n | +-----------------+ |\n | | return address | |\n | | previous fp ------+\n | | saved registers |\n | | local variables |\n | | ... | <-+\n | +-----------------+ |\n | | return address | |\n +------ previous fp | |\n | saved registers | |\n | local variables | |\n $fp --> | ... | |\n +-----------------+ |\n | return address | |\n | previous fp ------+\n | saved registers |\n $sp --> | local variables |\n +-----------------+<\/code><\/pre>\n<\/blockquote>\n2.1 \u7406\u89e3\u8fd9\u4e2a\u7a0b\u5e8f\u6808<\/h3>\n
2.2 \u5982\u4f55\u5224\u65ad\u8ffd\u8e2a\u7684\u7ec8\u70b9<\/h3>\n
PGROUNDDOWN<\/code>\u5b8f\u5c31\u53ef\u4ee5\u77e5\u9053\u5f53\u524d\u6808\u5e27\u5730\u5740\u6240\u5728\u7684\u9875\u3002\u6bd4\u8f83\u5f53\u524d\u6808\u5e27\u548c\u4e0b\u4e00\u4e2a\u6808\u5e27\u7684\u5730\u5740\u6240\u5728\u7684\u9875\u9762\u7684\u8d77\u59cb\u4f4d\u7f6e\u662f\u4e0d\u662f\u76f8\u540c\uff0c\u5c31\u53ef\u4ee5\u5224\u65ad\u6808\u5e27\u8ffd\u8e2a\u662f\u4e0d\u662f\u8fbe\u5230\u4e86\u7ec8\u70b9\u3002<\/p>\n2.3 \u6839\u636ehints\u6dfb\u52a0\u76f8\u5e94\u7684\u51fd\u6570<\/h3>\n
2.4 \u4ee3\u7801\u5b9e\u73b0<\/h3>\n
void\nbacktrace(void) {\n printf("backtrace:\\n");\n\n uint64 fp = r_fp();\n\n while (1) {\n printf("%p\\n", *((uint64 *)(fp - 8)));\n uint64 prefp = *((uint64 *)(fp - 16));\n\n if (PGROUNDDOWN(fp) != PGROUNDDOWN(prefp)) {\n break;\n }\n\n fp = prefp;\n }\n}<\/code><\/pre>\npanic<\/code>\u51fd\u6570\u4e2d\u8c03\u7528\uff0c\u4ee5\u8ffd\u8e2a\u9519\u8bef\u4fe1\u606f\u3002<\/p>\n3 Alarm (hard)<\/h2>\n
\n
3.1 \u90e8\u7f72sigalarm\u548csigreturn\u4e24\u4e2a\u7cfb\u7edf\u8c03\u7528<\/h3>\n
lab syscall<\/code>\u4e2d\u58f0\u660e\u7cfb\u7edf\u8c03\u7528\u7684\u65b9\u6cd5\uff0c\u58f0\u660e\u8fd9\u4e24\u4e2a\u7cfb\u7edf\u8c03\u7528\u51fd\u6570\u3002<\/p>\n3.2 \u5206\u6790trap\u7684\u8fc7\u7a0b<\/h3>\n
\n
ecall<\/code>\u8fdb\u5165\u5185\u6838\u6001\u3002<\/li>\nusertrap<\/code>\u51fd\u6570\u3002<\/li>\n3.3 sigalarm<\/h3>\n
which_dev<\/code>\u8868\u793a\u8be5\u8c03\u7528\u7684\u7c7b\u578b\uff0c\u5982\u679c\u503c\u4e3a2\uff0c\u5219\u8be5\u4e2d\u65ad\u7c7b\u578b\u662f\u65f6\u949f\u5468\u671f\u7684\u4e2d\u65ad\u3002\u5982\u679c\u662f\u65f6\u949f\u5468\u671f\u7684\u4e2d\u65ad\uff0c\u6211\u4e48\u600e\u4e48\u77e5\u9053\u8fc7\u4e86\u591a\u5c11\u4e2a\u65f6\u949f\u5468\u671f\uff0c\u4ee5\u53ca\u7528\u6237\u8981\u6c42\u7684\u591a\u5c11\u65f6\u949f\u5468\u671f\u8fc7\u540e\u6267\u884c\u7528\u6237\u4ee3\u7801\uff0c\u4ee5\u53ca\u7528\u6237\u4ee3\u7801\u5730\u5740\u5462\u3002\u4e3a\u4e86\u50a8\u5b58\u8fd9\u4e9b\u4fe1\u606f\uff0c\u6211\u4eec\u5728\u8fdb\u7a0b\u7ed3\u6784\u4f53struct proc<\/code>\u4e2d\u8bbe\u7f6e\u8fd9\u4e9b\u4fe1\u606f\u3002<\/p>\nint alarm_interval;\nvoid (*user_handler)();\nint ticks_pass;<\/code><\/pre>\nsyscall<\/code>\u7684\u65f6\u5019\uff0c\u6211\u4eec\u4ece\u7528\u6237\u6001\u83b7\u5f97\u5468\u671f\u95f4\u9694\u6570\uff0c\u548c\u7528\u6237\u4ee3\u7801\u5730\u5740\u3002<\/p>\nuint64\nsys_sigalarm(void)\n{\n int interval;\n uint64 uhandler;\n\n argint(0, &interval);\n argaddr(1, &uhandler);\n\n struct proc *p = myproc();\n\n p->alarm_interval = interval;\n p->user_handler = (void (*)())uhandler;\n p->ticks_pass = 0;\n\n return 0;\n}<\/code><\/pre>\nusertrap<\/code>\u51fd\u6570\u83b7\u5f97\u4e86\u65f6\u949f\u4e2d\u65ad\u4e4b\u540e\uff0c\u5982\u679c\u8be5\u8fdb\u7a0b\u6709\u4e2d\u65ad\u95f4\u9694\u8981\u6c42\uff0c\u5219\u5728tickspass\u4e0a\u52a0\u4e00\uff0c\u5982\u679ctickspass\u6570\u7b49\u4e8e\u4e2d\u65ad\u95f4\u9694\u8981\u6c42\uff0c\u5219\u5c06p->trapframe<\/code>\u57df\u4e2d\u7684epc<\/code>\uff08\u8868\u793a\u8fd4\u56de\u7528\u6237\u6001\u7684\u7a0b\u5e8f\u8ba1\u6570\u5668\uff09\u8bbe\u7f6e\u4e3a\u7528\u6237\u8981\u6c42\u7684\u4ee3\u7801\u5730\u5740\uff0c\u8fd9\u4e2a\u5730\u5740\u53ef\u80fd\u4e3a0\uff0c\u6240\u4ee5\u6211\u4eec\u4e0d\u80fd\u4f7f\u7528\u7528\u6237\u4ee3\u7801\u5730\u5740\u6765\u5224\u65ad\u7528\u6237\u662f\u5426\u6709\u5468\u671f\u4efb\u52a1\u8bf7\u6c42<\/strong>\uff0c\u7136\u540e\u5c06tickspass\u7f6e\u4e3a0\uff0c\u91cd\u65b0\u5f00\u59cb\u8ba1\u6570\u3002<\/p>\nif (p->alarm_interval) {\n p->ticks_pass++;\n if (p->ticks_pass == p->alarm_interval) {\n p->ticks_pass = 0;\n p->trapframe->epc = (uint64)p->user_handler;\n }\n}<\/code><\/pre>\n3.4 \u5904\u7406sigalarm\u7528\u6237\u6001\u7ed3\u675f\u6062\u590d\u8fdb\u7a0b<\/h3>\n
\n
sigreturn<\/code>\u7cfb\u7edf\u8c03\u7528\u3002\u6211\u4eec\u53ef\u4ee5\u5728sigreturn<\/code>\u5904\u7406\u6062\u590d\u7528\u6237\u8fdb\u7a0b\u3002<\/p>\n3.4.1 \u9700\u8981\u4fdd\u5b58\u7684\u5bc4\u5b58\u5668<\/h4>\n
![\"image-20221101150634287\"](\"http:\/\/43.139.35.156\/upload\/2022\/11\/image-20221101150634287.png\")
<\/div><\/p>\nRISC-V ISA<\/code>\u53c2\u8003\u6587\u6863\u4e2d\u5f97\u5230\uff0c\u9664\u4e86t0, t1, t2, ... , t6<\/code>\u662f\u5360\u65f6\u5bc4\u5b58\u5668\u5916\uff0c\u5176\u4ed6\u5bc4\u5b58\u5668\u90fd\u6709\u5b9e\u9645\u7684\u7528\u9014\uff08\u7b14\u8005\u4fdd\u9669\u8d77\u89c1\uff0c\u90fd\u628a\u8fd9\u4e9b\u5bc4\u5b58\u5668\u7684\u4fe1\u606f\u90fd\u53e6\u5b58\u8d77\u6765\u4e86\uff09\uff0c\u800c\u4e14\u8fdb\u7a0b\u7ed3\u6784\u4f53\u4e2d\u6709context<\/code>\u53d8\u91cf\uff0c\u4fdd\u5b58\u7684\u662f\u8be5\u8fdb\u7a0b\u88ab\u6682\u505c\u4e4b\u540e\u7684\u5bc4\u5b58\u5668\u4fe1\u606f\uff0c\u4ee5\u4fbf\u4e4b\u540e\u91cd\u65b0\u8fd0\u884c\u4e4b\u540e\u91cd\u65b0\u6062\u590d\u8fdb\u7a0b\u72b6\u6001\u3002\u53ef\u4ee5\u6a21\u4eff\uff0c\u8bbe\u7f6e\u4e00\u4e2ausercontext<\/code>\u53d8\u91cf\uff0c\u6765\u4fdd\u5b58\u8c03\u7528\u7528\u6237\u4ee3\u7801\u4e4b\u524d\uff0c\u4fdd\u5b58\u5728\u6b64\u4e4b\u524d\u7528\u6237\u6001\u5bc4\u5b58\u5668\u7684\u72b6\u6001\u3002<\/p>\nstruct usercontext {\n uint64 ra;\n uint64 sp;\n uint64 gp;\n uint64 tp;\n uint64 epc;\n\n \/* 96 *\/ uint64 s0;\n \/* 104 *\/ uint64 s1;\n \/* 112 *\/ uint64 a0;\n \/* 120 *\/ uint64 a1;\n \/* 128 *\/ uint64 a2;\n \/* 136 *\/ uint64 a3;\n \/* 144 *\/ uint64 a4;\n \/* 152 *\/ uint64 a5;\n \/* 160 *\/ uint64 a6;\n \/* 168 *\/ uint64 a7;\n \/* 176 *\/ uint64 s2;\n \/* 184 *\/ uint64 s3;\n \/* 192 *\/ uint64 s4;\n \/* 200 *\/ uint64 s5;\n \/* 208 *\/ uint64 s6;\n \/* 216 *\/ uint64 s7;\n \/* 224 *\/ uint64 s8;\n \/* 232 *\/ uint64 s9;\n \/* 240 *\/ uint64 s10;\n \/* 248 *\/ uint64 s11;\n};<\/code><\/pre>\n3.4.2 \u4fdd\u5b58\u5bc4\u5b58\u5668\u72b6\u6001<\/h4>\n
if (which_dev == 2) {\n if (p->alarm_interval) {\n p->ticks_pass++;\n if (p->ticks_pass == p->alarm_interval) {\n\n p->usercontext.epc = p->trapframe->epc;\n p->usercontext.ra = p->trapframe->ra;\n p->usercontext.sp = p->trapframe->sp;\n p->usercontext.gp = p->trapframe->gp;\n p->usercontext.tp = p->trapframe->tp;\n p->usercontext.s0 = p->trapframe->s0;\n p->usercontext.s1 = p->trapframe->s1;\n p->usercontext.a0 = p->trapframe->a0;\n p->usercontext.a1 = p->trapframe->a1;\n p->usercontext.a2 = p->trapframe->a2;\n p->usercontext.a3 = p->trapframe->a3;\n p->usercontext.a4 = p->trapframe->a4;\n p->usercontext.a5 = p->trapframe->a5;\n p->usercontext.a6 = p->trapframe->a6;\n p->usercontext.a7 = p->trapframe->a7;\n p->usercontext.s2 = p->trapframe->s2;\n p->usercontext.s3 = p->trapframe->s3;\n p->usercontext.s4 = p->trapframe->s4;\n p->usercontext.s5 = p->trapframe->s5;\n p->usercontext.s6 = p->trapframe->s6;\n p->usercontext.s7 = p->trapframe->s7;\n p->usercontext.s8 = p->trapframe->s8;\n p->usercontext.s9 = p->trapframe->s9;\n p->usercontext.s10 = p->trapframe->s10;\n p->usercontext.s11 = p->trapframe->s11;\n\n p->ticks_pass = 0;\n p->trapframe->epc = (uint64)p->user_handler;\n }\n }\n}<\/code><\/pre>\n3.4.3 \u6062\u590d\u5bc4\u5b58\u5668\u72b6\u6001<\/h4>\n
sigreturn<\/code>\uff0c\u8fdb\u5165\u8be5\u51fd\u6570\u540e\uff0c\u6211\u4eec\u6062\u590d\u5bc4\u5b58\u5668\u3002\u4e4b\u540e\u4f1a\u5728usertrap<\/code>\u51fd\u6570\u8fd4\u56de\u5230\u7528\u6237\u6001\u3002<\/p>\nuint64\nsys_sigreturn()\n{\n struct proc *p = myproc();\n\n p->trapframe->ra = p->usercontext.ra;\n p->trapframe->sp = p->usercontext.sp;\n p->trapframe->gp = p->usercontext.gp;\n p->trapframe->tp = p->usercontext.tp;\n p->trapframe->s0 = p->usercontext.s0;\n p->trapframe->s1 = p->usercontext.s1;\n p->trapframe->a0 = p->usercontext.a0;\n p->trapframe->a1 = p->usercontext.a1;\n p->trapframe->a2 = p->usercontext.a2;\n p->trapframe->a3 = p->usercontext.a3;\n p->trapframe->a4 = p->usercontext.a4;\n p->trapframe->a5 = p->usercontext.a5;\n p->trapframe->a6 = p->usercontext.a6;\n p->trapframe->a7 = p->usercontext.a7;\n p->trapframe->s2 = p->usercontext.s2;\n p->trapframe->s3 = p->usercontext.s3;\n p->trapframe->s4 = p->usercontext.s4;\n p->trapframe->s5 = p->usercontext.s5;\n p->trapframe->s6 = p->usercontext.s6;\n p->trapframe->s7 = p->usercontext.s7;\n p->trapframe->s8 = p->usercontext.s8;\n p->trapframe->s9 = p->usercontext.s9;\n p->trapframe->s10 = p->usercontext.s10;\n p->trapframe->s11 = p->usercontext.s11;\n p->trapframe->epc = p->usercontext.epc;\n\n return 0;\n}<\/code><\/pre>\n3.4.4 \u907f\u514d\u91cd\u590d\u8c03\u7528<\/h4>\n
alarmstatus<\/code>\u3002\u5f53\u65f6\u949f\u5468\u671f\u6570\u8fbe\u5230\u7528\u6237\u8981\u6c42\u7684\u5468\u671f\u6570\u4e4b\u540e\uff0c\u6211\u4eec\u8bbe\u7f6e\u8fd9\u4e2a\u6807\u8bb0\u4f4d\uff0c\u5f53\u7528\u6237\u8c03\u7528\u4e86sigreturn<\/code>\u51fd\u6570\u65f6\uff0c\u6211\u4eec\u5c06\u8be5\u53d8\u91cf\u8bbe\u7f6e\u4e3a0\u3002<\/p>\n------trap,c: usertrap--------\nif (.... && p->alarmstatus == 0) {\n ...\n p->alarmstatus = 1;\n}\n\n------syscall.c\/sys_sigreturn-------\nvoid\n sys_sigreturn()\n{\n ...\n p->alarmstatus = 0;\n}<\/code><\/pre>\n3.4.5 \u4fdd\u62a4a0\u5bc4\u5b58\u5668<\/h4>\n
sigreturn<\/code>\u7684\u8fd4\u56de\u503c\u3002<\/p>\nsigreturn<\/code>\u7684\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\nuint64\nsys_sigreturn()\n{\n struct proc *p = myproc();\n\n p->trapframe->ra = p->usercontext.ra;\n p->trapframe->sp = p->usercontext.sp;\n p->trapframe->gp = p->usercontext.gp;\n p->trapframe->tp = p->usercontext.tp;\n p->trapframe->s0 = p->usercontext.s0;\n p->trapframe->s1 = p->usercontext.s1;\n p->trapframe->a0 = p->usercontext.a0;\n p->trapframe->a1 = p->usercontext.a1;\n p->trapframe->a2 = p->usercontext.a2;\n p->trapframe->a3 = p->usercontext.a3;\n p->trapframe->a4 = p->usercontext.a4;\n p->trapframe->a5 = p->usercontext.a5;\n p->trapframe->a6 = p->usercontext.a6;\n p->trapframe->a7 = p->usercontext.a7;\n p->trapframe->s2 = p->usercontext.s2;\n p->trapframe->s3 = p->usercontext.s3;\n p->trapframe->s4 = p->usercontext.s4;\n p->trapframe->s5 = p->usercontext.s5;\n p->trapframe->s6 = p->usercontext.s6;\n p->trapframe->s7 = p->usercontext.s7;\n p->trapframe->s8 = p->usercontext.s8;\n p->trapframe->s9 = p->usercontext.s9;\n p->trapframe->s10 = p->usercontext.s10;\n p->trapframe->s11 = p->usercontext.s11;\n p->trapframe->epc = p->usercontext.epc;\n\n p->alarmstatus = 0;\n\n return p->usercontext.a0;\n}<\/code><\/pre>\n3.5 \u8003\u8651\u5bf9\u58f0\u660e\u7684\u53d8\u91cf\u7684\u5206\u914d\u548c\u91ca\u653e<\/h3>\n
alarm_interval<\/code>\/userhandler<\/code>\/usercontext<\/code>\/alarmstatus<\/code>\/ticks_pass<\/code>\uff0c\u8fdb\u7a0b\u521b\u5efa\u521d\u671f\u8981\u5168\u90e8\u7f6e0\uff0c\u8fdb\u7a0b\u7ed3\u675f\u4e5f\u5168\u90e8\u5f52\u96f6\u3002<\/p>\n---allocproc---\n{\n ....\n memset(&p->usercontext, 0, sizeof(p->usercontext));\n p->alarm_interval = 0;\n p->user_handler = 0;\n p->ticks_pass = 0;\n p->alarmstatus = 0;\n ....\n}\n\n---freeproc---\n{\n ....\n p->alarm_interval = 0;\n p->user_handler = 0;\n p->ticks_pass = 0;\n p->alarmstatus = 0;\n ....\n}<\/code><\/pre>\n4 END<\/h2>\n
== Test answers-traps.txt == answers-traps.txt: OK \n== Test backtrace test == \n$ make qemu-gdb\nbacktrace test: OK (4.0s) \n== Test running alarmtest == \n$ make qemu-gdb\n(6.2s) \n== Test alarmtest: test0 == \n alarmtest: test0: OK \n== Test alarmtest: test1 == \n alarmtest: test1: OK \n== Test alarmtest: test2 == \n alarmtest: test2: OK \n== Test alarmtest: test3 == \n alarmtest: test3: OK \n== Test usertests == \n$ make qemu-gdb\nusertests: OK (204.3s) \n== Test time == \ntime: OK \nScore: 95\/95<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"