Princeton University COS 217: Introduction to Programming Systems Fall 2005 Final Exam Answers

Transcription

1 Priceto Uiversity COS 217: Itroductio to Programmig Systems Fall 2005 Fial Exam Aswers The exam was a three-hour, ope-book, ope-otes exam. Questio 1 (a) Sytax error: Ivalid declaratio statemet o lie 2. Sytax error: Utermiated commet o lie 3. Sematic error: Icorrect computatio o lie 5. it foo(it ) it 2, 3; /* This fuctio is busted */ 2 = * ; 3 = 2 * ; pritf( =%d, ^2 = %d, ^3 = %d\,, 2, 3); retur 0; Questio 1 (b) %s is a strig is a strig Questio 1 (c) x = 12.3 i = 45 y =.6 Questio 1 (d) 4 Questio 1 (e) 110 Questio 1 (f) mystery(i) prits the value of i as a biary umber. Questio 1 (g) 65 (decimal) = (biary) 14 (decimal) = (biary) -14 (decimal) = (biary) (biary) = 51 (decimal) Questio 1 (h) A virtual memory address cosists of two parts: a virtual page umber ad a offset. The hardware uses the process's virtual page table to traslate the virtual page umber ito the page's start address i memory. It the adds the offset to that page start address to form the physical address. Page 1 of 6

2 Questio 1 (i) A fuctio call executes i user mode. A system call executes i privileged (alias supervisor) mode. A fuctio call is executed via a call istructio. A system call is executed via a it (iterrupt) istructio. Questio 1 (j) The I/O fuctios declared i stdio.h do bufferig for efficiecy. Physically readig data from ad writig data to devices is expesive. Bufferig data i memory allows physical I/O to occur less frequetly. Callig the fflush() fuctio causes all data that is buffered for a specified output stream to be writte to its physical device. Questio 1 (k) The alarm() fuctio causes a SIGALRM sigal after a delay measured i real (alias wallclock) time. The setitimer() fuctio causes a SIGPROF sigal after a delay measured i virtual (alias CPU, alias system) time. Questio 2 #defie _GNU_SOURCE /* Must defie _GNU_SOURCE so the defiitio of the sigset_t type is icluded from sigal.h. With _GNU_SOURCE defied, a sigal is ot automatically reset to its default hadler whe it occurs. So there is o eed to call sigal() ear the ed of the sigal's hadler. */ #iclude <stdio.h> #iclude <stdlib.h> #iclude <sigal.h> #iclude <assert.h> #iclude <uistd.h> eum MAX_SIGINT_COUNT = 2; eum MAX_SIGALRM_COUNT = 10; eum ALARM_SECONDS = 1; static it isigitcout = 0; static void sigithadler(it isigal) isigitcout++; if (isigitcout == MAX_SIGINT_COUNT) exit(exit_success); static void sigalrmhadler(it isigal) static it isigalrmcout = MAX_SIGALRM_COUNT + 1; isigalrmcout--; if (isigalrmcout == 0) pritf("happy New Year!\"); isigalrmcout = MAX_SIGALRM_COUNT; isigitcout = 0; pritf("%d... ", isigalrmcout); fflush(stdout); it mai(void) void (*pfret)(it); it iret; sigset_t ssigset; Page 2 of 6

3 /* Make sure SIGALRM is ot blocked. */ sigemptyset(&ssigset); sigaddset(&ssigset, SIGALRM); iret = sigprocmask(sig_unblock, &ssigset, NULL); assert(iret == 0); pfret = sigal(sigalrm, sigalrmhadler); pfret = sigal(sigint, sigithadler); /* or raise(sigalrm); */ /* or kill(getpid(), SIGALRM); */ for (;;) ; Alterate Aswer: #defie _GNU_SOURCE /* Must defie _GNU_SOURCE so the defiitio of the sigset_t type is icluded from sigal.h. With _GNU_SOURCE defied, a sigal is ot automatically reset to its default hadler whe it occurs. So there is o eed to call sigal() ear the ed of the sigal's hadler. */ #iclude <stdio.h> #iclude <stdlib.h> #iclude <sigal.h> #iclude <assert.h> #iclude <uistd.h> eum MAX_SIGALRM_COUNT = 10; eum ALARM_SECONDS = 1; static void sigithadler(it isigal) /* Reset SIGINT to its default hadler. */ sigal(sigint, SIG_DFL); static void sigalrmhadler(it isigal) static it isigalrmcout = MAX_SIGALRM_COUNT + 1; void (*pfret)(it); isigalrmcout--; if (isigalrmcout == 0) pritf("happy New Year!\"); isigalrmcout = MAX_SIGALRM_COUNT; pfret = sigal(sigint, sigithadler); pritf("%d... ", isigalrmcout); fflush(stdout); it mai(void) void (*pfret)(it); it iret; sigset_t ssigset; /* Make sure SIGALRM is ot blocked. */ Page 3 of 6

4 sigemptyset(&ssigset); sigaddset(&ssigset, SIGALRM); iret = sigprocmask(sig_unblock, &ssigset, NULL); assert(iret == 0); pfret = sigal(sigalrm, sigalrmhadler); pfret = sigal(sigint, sigithadler); /* or raise(sigalrm); */ /* or kill(getpid(), SIGALRM); */ for (;;) ; Questio 3 (a) LDI ad JNZ use immediate addressig. STORE, READ, ad NANDM use direct addressig. Questio 3 (b) READ (0x80) SHR STORE (0x80) LDI 0x7f NANDM (0x80) LDI 0xff NANDM (0x80) Questio 3 (c) shift_left_start: LDI 0x01 shift_left_cotiue: SHL JNZ shift_left_cotiue shift_right_start: LDI 0x80 shift_right_cotiue: LSHR JNZ shift_right_cotiue LDI shift_left_start JMP Page 4 of 6

5 Questio 4 all S a o F a Questio 5 gcc -c myprog.c gcc -c oe.c gcc -c two.c gcc -c three.c gcc -c four.c $ touch myprog.c gcc -c myprog.c make: Nothig to be doe for `myprog'. $ touch two.h gcc -c two.c $ touch four.h gcc -c two.c gcc -c three.c gcc -c four.c Questio 6 #iclude <stdio.h> #iclude <stdlib.h> #iclude <strig.h> #iclude <assert.h> #defie MAX_CHARS_PER_LINE 256 #defie MAX_LINES 10 it mai(void) char pclie[max_chars_per_line]; char *ppclies[max_lines]; it i; for (i = 0; i < MAX_LINES; i++) ppclies[i] = NULL; Page 5 of 6

6 while (fgets(pclie, MAX_CHARS_PER_LINE, stdi)!= NULL) free(ppclies[0]); for (i = 0; i < MAX_LINES-1; i++) ppclies[i] = ppclies[i+1]; ppclies[max_lines-1] = (char*)malloc(strle(pclie) + 1); assert(ppclies[max_lines-1]!= NULL); strcpy(ppclies[max_lines-1], pclie); for (i = 0; i < MAX_LINES; i++) if (ppclies[i]!= NULL) fputs(ppclies[i], stdout); for (i = 0; i < MAX_LINES; i++) free(ppclies[i]); retur 0; Copyright 2006 by Robert M. Dodero, Jr. Page 6 of 6