reverse engineering

1 files changed, 675 insertions, 0 deletions

diff --git a/tshref.c b/tshref.c
new file mode 100644
index 0000000..0afb216
--- /dev/null
+++ b/tshref.c
@@ -0,0 +1,675 @@
+// reverse engineering of tshref
+// ft. CSAPP 3e
+
+/* 
+ * tsh - A tiny shell program with job control
+ * 
+ * <Put your name and login ID here>
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <ctype.h>
+#include <signal.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <errno.h>
+
+/* Misc manifest constants */
+#define MAXLINE    1024   /* max line size */
+#define MAXARGS     128   /* max args on a command line */
+#define MAXJOBS      16   /* max jobs at any point in time */
+#define MAXJID    1<<16   /* max job ID */
+
+/* Job states */
+#define UNDEF 0 /* undefined */
+#define FG 1    /* running in foreground */
+#define BG 2    /* running in background */
+#define ST 3    /* stopped */
+
+/* 
+ * Jobs states: FG (foreground), BG (background), ST (stopped)
+ * Job state transitions and enabling actions:
+ *     FG -> ST  : ctrl-z
+ *     ST -> FG  : fg command
+ *     ST -> BG  : bg command
+ *     BG -> FG  : fg command
+ * At most 1 job can be in the FG state.
+ */
+
+/* Global variables */
+extern char **environ;      /* defined in libc */
+char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
+int verbose = 0;            /* if true, print additional output */
+int nextjid = 1;            /* next job ID to allocate */
+char sbuf[MAXLINE];         /* for composing sprintf messages */
+
+struct job_t {              /* The job struct */
+    pid_t pid;              /* job PID */
+    int jid;                /* job ID [1, 2, ...] */
+    int state;              /* UNDEF, BG, FG, or ST */
+    char cmdline[MAXLINE];  /* command line */
+};
+struct job_t jobs[MAXJOBS]; /* The job list */
+/* End global variables */
+
+
+/* Function prototypes */
+
+/* Here are the functions that you will implement */
+void eval(char *cmdline);
+int builtin_cmd(char **argv);
+void do_bgfg(char **argv);
+void waitfg(pid_t pid);
+
+void sigchld_handler(int sig);
+void sigtstp_handler(int sig);
+void sigint_handler(int sig);
+
+/* Here are helper routines that we've provided for you */
+int parseline(const char *cmdline, char **argv); 
+void sigquit_handler(int sig);
+
+void clearjob(struct job_t *job);
+void initjobs(struct job_t *jobs);
+int maxjid(struct job_t *jobs); 
+int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
+int deletejob(struct job_t *jobs, pid_t pid); 
+pid_t fgpid(struct job_t *jobs);
+struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
+struct job_t *getjobjid(struct job_t *jobs, int jid); 
+int pid2jid(pid_t pid); 
+void listjobs(struct job_t *jobs);
+
+void usage(void);
+void unix_error(char *msg);
+void app_error(char *msg);
+typedef void handler_t(int);
+handler_t *Signal(int signum, handler_t *handler);
+
+/*
+ * main - The shell's main routine 
+ */
+int main(int argc, char **argv) 
+{
+    char c;
+    char cmdline[MAXLINE];
+    int emit_prompt = 1; /* emit prompt (default) */
+
+    /* Redirect stderr to stdout (so that driver will get all output
+     * on the pipe connected to stdout) */
+    dup2(1, 2);
+
+    /* Parse the command line */
+    while ((c = getopt(argc, argv, "hvp")) != EOF) {
+        switch (c) {
+        case 'h':             /* print help message */
+            usage();
+	    break;
+        case 'v':             /* emit additional diagnostic info */
+            verbose = 1;
+	    break;
+        case 'p':             /* don't print a prompt */
+            emit_prompt = 0;  /* handy for automatic testing */
+	    break;
+	default:
+            usage();
+	}
+    }
+
+    /* Install the signal handlers */
+
+    /* These are the ones you will need to implement */
+    Signal(SIGINT,  sigint_handler);   /* ctrl-c */
+    Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
+    Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */
+
+    /* This one provides a clean way to kill the shell */
+    Signal(SIGQUIT, sigquit_handler); 
+
+    /* Initialize the job list */
+    initjobs(jobs);
+
+    /* Execute the shell's read/eval loop */
+    while (1) {
+
+	/* Read command line */
+	if (emit_prompt) {
+	    printf("%s", prompt);
+	    fflush(stdout);
+	}
+	if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
+	    app_error("fgets error");
+	if (feof(stdin)) { /* End of file (ctrl-d) */
+	    fflush(stdout);
+	    exit(0);
+	}
+
+	/* Evaluate the command line */
+	eval(cmdline);
+	fflush(stdout);
+	fflush(stdout);
+    } 
+
+    exit(0); /* control never reaches here */
+}
+  
+/* 
+ * eval - Evaluate the command line that the user has just typed in
+ * 
+ * If the user has requested a built-in command (quit, jobs, bg or fg)
+ * then execute it immediately. Otherwise, fork a child process and
+ * run the job in the context of the child. If the job is running in
+ * the foreground, wait for it to terminate and then return.  Note:
+ * each child process must have a unique process group ID so that our
+ * background children don't receive SIGINT (SIGTSTP) from the kernel
+ * when we type ctrl-c (ctrl-z) at the keyboard.  
+*/
+void eval(char *cmdline) 
+{
+    char *argv[MAXARGS];
+    int bg;
+    pid_t pid;
+    sigset_t mask;
+
+    bg = parseline(cmdline, argv);
+    if (argv[0] == NULL)
+        return;
+
+    if (builtin_cmd(argv))
+        return;
+
+    if (sigemptyset(&mask) < 0)
+        unix_error("sigemptyset error");
+    if (sigaddset(&mask, SIGCHLD) != 0 ||
+        sigaddset(&mask, SIGINT)  != 0 ||
+        sigaddset(&mask, SIGTSTP) != 0)
+        unix_error("sigaddset error");
+    if (sigprocmask(SIG_BLOCK, &mask, NULL) < 0)
+        unix_error("sigprocmask error");
+
+    if ((pid = fork()) < 0)
+        unix_error("fork error");
+
+    if (pid == 0) {
+        sigprocmask(SIG_UNBLOCK, &mask, NULL);
+        if (setpgid(0, 0) < 0)
+            unix_error("setpgid error");
+        if (execve(argv[0], argv, environ) < 0) {
+            printf("%s: Command not found\n", argv[0]);
+            exit(0);
+        }
+    }
+
+    addjob(jobs, pid, bg ? BG : FG, cmdline);
+    sigprocmask(SIG_UNBLOCK, &mask, NULL);
+
+    if (bg)
+        printf("[%d] (%d) %s", pid2jid(pid), pid, cmdline);
+    else
+        waitfg(pid);
+}
+
+/* 
+ * parseline - Parse the command line and build the argv array.
+ * 
+ * Characters enclosed in single quotes are treated as a single
+ * argument.  Return true if the user has requested a BG job, false if
+ * the user has requested a FG job.  
+ */
+int parseline(const char *cmdline, char **argv) 
+{
+    static char array[MAXLINE]; /* holds local copy of command line */
+    char *buf = array;          /* ptr that traverses command line */
+    char *delim;                /* points to first space delimiter */
+    int argc;                   /* number of args */
+    int bg;                     /* background job? */
+
+    strcpy(buf, cmdline);
+    buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
+    while (*buf && (*buf == ' ')) /* ignore leading spaces */
+	buf++;
+
+    /* Build the argv list */
+    argc = 0;
+    if (*buf == '\'') {
+	buf++;
+	delim = strchr(buf, '\'');
+    }
+    else {
+	delim = strchr(buf, ' ');
+    }
+
+    while (delim) {
+	argv[argc++] = buf;
+	*delim = '\0';
+	buf = delim + 1;
+	while (*buf && (*buf == ' ')) /* ignore spaces */
+	       buf++;
+
+	if (*buf == '\'') {
+	    buf++;
+	    delim = strchr(buf, '\'');
+	}
+	else {
+	    delim = strchr(buf, ' ');
+	}
+    }
+    argv[argc] = NULL;
+    
+    if (argc == 0)  /* ignore blank line */
+	return 1;
+
+    /* should the job run in the background? */
+    if ((bg = (*argv[argc-1] == '&')) != 0) {
+	argv[--argc] = NULL;
+    }
+    return bg;
+}
+
+/* 
+ * builtin_cmd - If the user has typed a built-in command then execute
+ *    it immediately.  
+ */
+int builtin_cmd(char **argv) 
+{
+    if (!strcmp(argv[0], "quit"))
+        exit(0);
+
+    if (!strcmp(argv[0], "jobs")) {
+        listjobs(jobs);
+        return 1;
+    }
+
+    if (!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg")) {
+        do_bgfg(argv);
+        return 1;
+    }
+
+    if (!strcmp(argv[0], "&"))
+        return 1;
+
+    return 0;
+}
+
+/* 
+ * do_bgfg - Execute the builtin bg and fg commands
+ */
+void do_bgfg(char **argv) 
+{
+    struct job_t *job = NULL;
+    long id;
+
+    if (argv[1] == NULL) {
+        printf("%s command requires PID or %%jobid argument\n", argv[0]);
+        return;
+    }
+
+    if (isdigit(argv[1][0])) {
+        id = strtol(argv[1], NULL, 10);
+        job = getjobpid(jobs, (pid_t)id);
+        if (id <= 0 || job == NULL) {
+            printf("(%ld): No such process\n", id);
+            return;
+        }
+    } else if (argv[1][0] == '%') {
+        id = strtol(argv[1] + 1, NULL, 10);
+        job = getjobjid(jobs, (int)id);
+        if (id <= 0 || job == NULL) {
+            printf("%s: No such job\n", argv[1]);
+            return;
+        }
+    } else {
+        printf("%s: argument must be a PID or %%jobid\n", argv[0]);
+        return;
+    }
+
+    if (!strcmp(argv[0], "bg")) {
+        if (kill(-job->pid, SIGCONT) < 0)
+            unix_error("kill (SIGCONT)");
+        job->state = BG;
+        printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
+    } else if (!strcmp(argv[0], "fg")) {
+        if (kill(-job->pid, SIGCONT) < 0)
+            unix_error("kill (SIGCONT)");
+        job->state = FG;
+        waitfg(job->pid);
+    } else {
+        printf("do_bgfg: Internal error: argv[0]=%s\n", argv[0]);
+        exit(0);
+    }
+}
+
+/* 
+ * waitfg - Block until process pid is no longer the foreground process
+ */
+void waitfg(pid_t pid)
+{
+    struct job_t *job;
+
+    if (pid <= 0)
+        return;
+
+    job = getjobpid(jobs, pid);
+    if (job == NULL)
+        return;
+
+    while (job->pid == pid && job->state == FG)
+        sleep(1);
+
+    if (verbose)
+        printf("waitfg: Process (%d) no longer the fg process\n", pid);
+}
+
+/*****************
+ * Signal handlers
+ *****************/
+
+/* 
+ * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
+ *     a child job terminates (becomes a zombie), or stops because it
+ *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
+ *     available zombie children, but doesn't wait for any other
+ *     currently running children to terminate.  
+ */
+void sigchld_handler(int sig) 
+{
+    pid_t pid;
+    int status;
+
+    if (verbose)
+        printf("sigchld_handler: entering\n");
+
+    while ((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0) {
+        if (WIFSTOPPED(status)) {
+            struct job_t *job = getjobpid(jobs, pid);
+            if (job == NULL) {
+                printf("Job (%d) not found\n", pid);
+                return;
+            }
+            job->state = ST;
+            fprintf(stdout, "Job [%d] (%d) stopped by signal %d\n",
+                    pid2jid(pid), pid, WSTOPSIG(status));
+        } else if (WIFSIGNALED(status)) {
+            int jid = pid2jid(pid);
+            deletejob(jobs, pid);
+            fprintf(stdout, "Job [%d] (%d) terminated by signal %d\n",
+                    jid, pid, WTERMSIG(status));
+        } else if (WIFEXITED(status)) {
+            deletejob(jobs, pid);
+        }
+    }
+
+    if (pid < 0 && errno != ECHILD)
+        unix_error("waitpid error");
+
+    if (verbose)
+        printf("sigchld_handler: exiting\n");
+}
+
+/* 
+ * sigint_handler - The kernel sends a SIGINT to the shell whenver the
+ *    user types ctrl-c at the keyboard.  Catch it and send it along
+ *    to the foreground job.  
+ */
+void sigint_handler(int sig) 
+{
+    pid_t pid;
+
+    if (verbose)
+        printf("sigint_handler: entering\n");
+
+    pid = fgpid(jobs);
+    if (pid > 0) {
+        if (kill(-pid, SIGINT) < 0)
+            unix_error("kill (SIGINT) error");
+    }
+
+    if (verbose)
+        printf("sigint_handler: exiting\n");
+}
+
+/*
+ * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
+ *     the user types ctrl-z at the keyboard. Catch it and suspend the
+ *     foreground job by sending it a SIGTSTP.  
+ */
+void sigtstp_handler(int sig) 
+{
+    pid_t pid;
+
+    if (verbose)
+        printf("sigtstp_handler: entering\n");
+
+    pid = fgpid(jobs);
+    if (pid > 0) {
+        if (kill(-pid, SIGTSTP) < 0)
+            unix_error("kill (SIGTSTP)");
+    }
+
+    if (verbose)
+        printf("sigtstp_handler: exiting\n");
+}
+
+/*********************
+ * End signal handlers
+ *********************/
+
+/***********************************************
+ * Helper routines that manipulate the job list
+ **********************************************/
+
+/* clearjob - Clear the entries in a job struct */
+void clearjob(struct job_t *job) {
+    job->pid = 0;
+    job->jid = 0;
+    job->state = UNDEF;
+    job->cmdline[0] = '\0';
+}
+
+/* initjobs - Initialize the job list */
+void initjobs(struct job_t *jobs) {
+    int i;
+
+    for (i = 0; i < MAXJOBS; i++)
+	clearjob(&jobs[i]);
+}
+
+/* maxjid - Returns largest allocated job ID */
+int maxjid(struct job_t *jobs) 
+{
+    int i, max=0;
+
+    for (i = 0; i < MAXJOBS; i++)
+	if (jobs[i].jid > max)
+	    max = jobs[i].jid;
+    return max;
+}
+
+/* addjob - Add a job to the job list */
+int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline) 
+{
+    int i;
+    
+    if (pid < 1)
+	return 0;
+
+    for (i = 0; i < MAXJOBS; i++) {
+	if (jobs[i].pid == 0) {
+	    jobs[i].pid = pid;
+	    jobs[i].state = state;
+	    jobs[i].jid = nextjid++;
+	    if (nextjid > MAXJOBS)
+		nextjid = 1;
+	    strcpy(jobs[i].cmdline, cmdline);
+  	    if(verbose){
+	        printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
+            }
+            return 1;
+	}
+    }
+    printf("Tried to create too many jobs\n");
+    return 0;
+}
+
+/* deletejob - Delete a job whose PID=pid from the job list */
+int deletejob(struct job_t *jobs, pid_t pid) 
+{
+    int i;
+
+    if (pid < 1)
+	return 0;
+
+    for (i = 0; i < MAXJOBS; i++) {
+	if (jobs[i].pid == pid) {
+	    clearjob(&jobs[i]);
+	    nextjid = maxjid(jobs)+1;
+	    return 1;
+	}
+    }
+    return 0;
+}
+
+/* fgpid - Return PID of current foreground job, 0 if no such job */
+pid_t fgpid(struct job_t *jobs) {
+    int i;
+
+    for (i = 0; i < MAXJOBS; i++)
+	if (jobs[i].state == FG)
+	    return jobs[i].pid;
+    return 0;
+}
+
+/* getjobpid  - Find a job (by PID) on the job list */
+struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
+    int i;
+
+    if (pid < 1)
+	return NULL;
+    for (i = 0; i < MAXJOBS; i++)
+	if (jobs[i].pid == pid)
+	    return &jobs[i];
+    return NULL;
+}
+
+/* getjobjid  - Find a job (by JID) on the job list */
+struct job_t *getjobjid(struct job_t *jobs, int jid) 
+{
+    int i;
+
+    if (jid < 1)
+	return NULL;
+    for (i = 0; i < MAXJOBS; i++)
+	if (jobs[i].jid == jid)
+	    return &jobs[i];
+    return NULL;
+}
+
+/* pid2jid - Map process ID to job ID */
+int pid2jid(pid_t pid) 
+{
+    int i;
+
+    if (pid < 1)
+	return 0;
+    for (i = 0; i < MAXJOBS; i++)
+	if (jobs[i].pid == pid) {
+            return jobs[i].jid;
+        }
+    return 0;
+}
+
+/* listjobs - Print the job list */
+void listjobs(struct job_t *jobs) 
+{
+    int i;
+    
+    for (i = 0; i < MAXJOBS; i++) {
+	if (jobs[i].pid != 0) {
+	    printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
+	    switch (jobs[i].state) {
+		case BG: 
+		    printf("Running ");
+		    break;
+		case FG: 
+		    printf("Foreground ");
+		    break;
+		case ST: 
+		    printf("Stopped ");
+		    break;
+	    default:
+		    printf("listjobs: Internal error: job[%d].state=%d ", 
+			   i, jobs[i].state);
+	    }
+	    printf("%s", jobs[i].cmdline);
+	}
+    }
+}
+/******************************
+ * end job list helper routines
+ ******************************/
+
+
+/***********************
+ * Other helper routines
+ ***********************/
+
+/*
+ * usage - print a help message
+ */
+void usage(void) 
+{
+    printf("Usage: shell [-hvp]\n");
+    printf("   -h   print this message\n");
+    printf("   -v   print additional diagnostic information\n");
+    printf("   -p   do not emit a command prompt\n");
+    exit(1);
+}
+
+/*
+ * unix_error - unix-style error routine
+ */
+void unix_error(char *msg)
+{
+    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
+    exit(1);
+}
+
+/*
+ * app_error - application-style error routine
+ */
+void app_error(char *msg)
+{
+    fprintf(stdout, "%s\n", msg);
+    exit(1);
+}
+
+/*
+ * Signal - wrapper for the sigaction function
+ */
+handler_t *Signal(int signum, handler_t *handler) 
+{
+    struct sigaction action, old_action;
+
+    action.sa_handler = handler;  
+    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
+    action.sa_flags = SA_RESTART; /* restart syscalls if possible */
+
+    if (sigaction(signum, &action, &old_action) < 0)
+	unix_error("Signal error");
+    return (old_action.sa_handler);
+}
+
+/*
+ * sigquit_handler - The driver program can gracefully terminate the
+ *    child shell by sending it a SIGQUIT signal.
+ */
+void sigquit_handler(int sig) 
+{
+    printf("Terminating after receipt of SIGQUIT signal\n");
+    exit(1);
+}
+
+
+