111 lines
3.2 KiB
C
111 lines
3.2 KiB
C
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#include <assert.h>
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#include <fcntl.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/prctl.h>
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#include <sys/wait.h>
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#include <unistd.h>
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#include "signals.h"
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static void catch_loop (int);
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/* Convert the short signal name (NNN part of SIGNNN) to its number.
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Consult /usr/include/asm/signal.h for the number mappings. For
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this lab, hard-code the numbers; do not use the numeric constants.
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Return -1 if the name isn't one you need to look up. */
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int
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signal_lookup (char *name)
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{
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// TODO: Look up the numbers for INT, SEGV, KILL, and TSTP
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if (strcmp (name, "INT") == 0)
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return 2;
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if (strcmp (name, "SEGV") == 0)
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return 11;
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if (strcmp (name, "KILL") == 0)
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return 9;
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if (strcmp (name, "TSTP") == 0)
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return 20;
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return -1;
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}
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// Entry point for overriding a signal handler in this lab.
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void
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override (char *signal)
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{
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int sig = signal_lookup (signal);
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if (sig == SIGKILL)
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printf ("Received bad signal name: %s\n", signal);
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else
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catch_loop (sig);
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}
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// Generic signal handler. This function doesn't use the signal number
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// in the provided distribution.
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void
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sig_handler (int signum __attribute__ ((unused)))
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{
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// TODO: Complete this signal handler so that it writes the message
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// "Breaking out with signal %d\n" with the signal number that was
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// passed. Note that you cannot use printf() in a signal handler.
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// You must use write(). After writing the message, exit with return
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// code 37.
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//
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// HINT: If you fail integration tests and get a message that the
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// binary files are different, you may be writing an extra byte (the
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// null byte). You can make sure you avoid this by using strlen()
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// instead of trying to hard-code a length.
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char buf[128];
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snprintf (buf, 128, "Breaking out with signal %d\n", signum);
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write (STDOUT_FILENO, buf, strlen (buf));
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exit (37);
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}
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void
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catch_loop (int signum)
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{
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// sigaction(signum)
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// TODO: Override the signal handler for the signal number passed.
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// Then create a child that runs the following code:
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// prctl (PR_SET_PDEATHSIG, SIGKILL);
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// printf ("Child has started\n");
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// fflush (stdout);
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// while (1) ;
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struct sigaction sa = { 0 };
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sa.sa_handler = sig_handler;
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sigaction (signum, &sa, NULL);
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pid_t pid = fork ();
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if (pid == 0)
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{
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prctl (PR_SET_PDEATHSIG, SIGKILL);
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printf ("Child has started\n");
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fflush (stdout);
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while (1)
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pause ();
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}
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// HINT: You will NOT call sig_handler() directly here. Instead,
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// you must use sigaction() to modify the signal's interrupt handler
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// so that sig_handler() will be called later when the signal occurs.
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// After starting the child, the parent will call sleep (1) to wait
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// for 1 second before sending the signal to the child. The parent
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// must wait for the child to run (and exit), then print
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// "Child was stopped with status %d\n" with the child process's exit
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// status code, retrieved with waitpid(). Note that you will need to
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// call WEXITSTATUS() on the retrieved status code.
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sleep (1);
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int status = 0;
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kill (pid, signum);
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waitpid (pid, &status, 0);
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printf ("Child was stopped with status %d\n", WEXITSTATUS (status));
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}
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