src/commands/mdb/mdb.c

Go to the documentation of this file.

/*
 * mdb.c - MINIX program debugger
 *
 * Written by Bruce D. Szablak
 *
 * This free software is provided for non-commerical use. No warrantee
 * of fitness for any use is implied. You get what you pay for. Anyone
 * may make modifications and distribute them, but please keep this header
 * in the distribution.
 */

/*
 * Originally ported to MINIX-PC and MINIX-386 by Bruce Evans.
 * NB: the original sym.c and mdbdis86.c come from his 'db'
 *
 * Added by Philip Murton:
 *
 *  2.0         'Core' file functions
 *  2.1         Support for GNU exec
 *  2.2         Changes for Minix 1.6.x Beta
 *  2.3         Changes for Minix 1.7.0 and trace syscalls
 *  2.4         Changes for Minix 1.7.2 and clean up
 *  2.5.1       Add better help 
 *  2.5.2       Added io.c for logging options
 *  2.5.3       Minor changes and tested with Minix 1.7.4
 *  2.5.4       Command arguments processing improved (Thanks to Will Rose)
 *  2.6.0       Final Version for MINIX CD (Sept/96)
 */

#define _MAIN_MDB
#include "mdb.h"

#include <minix/type.h>

#include <stdio.h>
#include <signal.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <ctype.h>
#include <errno.h>
#include <sys/wait.h>
#define ptrace mdbtrace
#include <sys/ptrace.h>
#include <setjmp.h>
#include "proto.h"

#include "../../kernel/arch/i386/include/archtypes.h"
#include <kernel/const.h>
#include <kernel/type.h>
#include <kernel/proc.h>

/* buffer for proc and pointer to proc */
extern struct proc *prc;

#define MAXLINE 128
#define MAXARG  20

PRIVATE unsigned long lastexp = 0L;     /* last expression and segment */
PRIVATE int lastseg = NOSEG;
PRIVATE char *prog;             /* prog name */
PRIVATE char sbuf[MAXLINE];
PRIVATE char cbuf[MAXLINE];
PRIVATE char *cmd;              /* current command   */
PRIVATE char *cmdstart;         /* start of command  */
PRIVATE jmp_buf mainlp;


struct b_pnt {
  struct b_pnt *nxt, *prv;
  long addr;
  long oldval;
  char cmd[1];
} *b_head, *curpnt;

_PROTOTYPE( void main , (int argc, char *argv[]));

FORWARD _PROTOTYPE( void cleanup , (void));
FORWARD _PROTOTYPE( void freepnt , (struct b_pnt *pnt ));
FORWARD _PROTOTYPE( void findbpnt , (int verbose ));
FORWARD _PROTOTYPE( int exebpnt , (int restart ));
FORWARD _PROTOTYPE( void catch , (int sig ));
FORWARD _PROTOTYPE( int run , (char *name , char *argstr , int tflg ));
FORWARD _PROTOTYPE( int dowait , (void));
FORWARD _PROTOTYPE( void backtrace , (int all ));
FORWARD _PROTOTYPE( void modify , (long addr , int cnt , int verbose , int size ));
FORWARD _PROTOTYPE( void display , (long addr , int req ));
FORWARD _PROTOTYPE( void fill , (long addr , int req ));
FORWARD _PROTOTYPE( void dorun , (char *cmd ));
FORWARD _PROTOTYPE( void not_for_core , (void));
FORWARD _PROTOTYPE( void command , (void));


PRIVATE void cleanup()
{
  curpid = 0;
  curpnt = NULL;
  while (b_head) freepnt(b_head);
}

PRIVATE void findbpnt(verbose)
int verbose;
{
  for (curpnt = b_head; curpnt; curpnt = curpnt->nxt) {
        if (curpnt->addr == PC_MEMBER(prc) - BREAKPOINT_ADVANCE) {
                ptrace(T_SETINS, curpid, curpnt->addr, curpnt->oldval);
                ptrace(T_SETUSER, curpid, PC_OFF, curpnt->addr);
#if     SYSCALLS_SUPPORT
                if( syscalls ) 
                        do_syscall(curpnt->addr);
                else if (curpnt->cmd[0] != '\n')
#else
                if (curpnt->cmd[0] != '\n')
#endif
                        cmd = strcpy(cbuf, curpnt->cmd);
                else if (verbose)
                        Printf("Breakpoint hit.\n");
                return;
        }
  }
  if (verbose) Printf("Unknown breakpoint hit.\n");
}

PRIVATE int exebpnt(restart)
int restart;
{
  ptrace(T_STEP, curpid, 0L, (long) restart);
  if (dowait() == 0) return TRUE;
  ptrace(T_SETINS, curpid, curpnt->addr, BREAK(curpnt->oldval));
  curpnt = NULL;
  return FALSE;
}


PRIVATE void freepnt(pnt)
struct b_pnt *pnt;
{
  if (pnt->prv)
        pnt->prv->nxt = pnt->nxt;
  else
        b_head = pnt->nxt;
  if (pnt->nxt) pnt->nxt->prv = pnt->prv;
  if (curpid > 0) ptrace(T_SETINS, curpid, pnt->addr, pnt->oldval);
  free(pnt);
  if (pnt == curpnt) curpnt = NULL;
}


PUBLIC long breakpt(addr, cmd)
long addr;
char *cmd;
{
  struct b_pnt *new;

  if (curpid <= 0) {
        Printf("No active process.\n");
        return 0L;
  }
  for (new = b_head; new; new = new->nxt)
        if (new->addr == addr) {
                Printf("Breakpoint already exists here.\n");
                return 0L;
        }
  new = (struct b_pnt *) malloc(sizeof(struct b_pnt) + strlen(cmd));
  if (new == NULL) {
        Printf("No room for new breakpoint.\n");
        return 0L;
  }
  new->nxt = b_head;
  new->prv = 0;
  if (b_head) b_head->prv = new;
  b_head = new;
  new->addr = addr;
  strcpy(new->cmd, cmd);
  new->oldval = ptrace(T_GETINS, curpid, addr, 0L);
  ptrace(T_SETINS, curpid, addr, BREAK(new->oldval));
  if (ptrace(T_GETINS, curpid, addr, 0L) != BREAK(new->oldval)) {
        do_error("Can't set breakpoint");
        freepnt(new);
        return 0L;
  }
  return new->oldval;
}

PRIVATE void catch(sig)
int sig;
{
  signal(sig, catch);
  if (sig == SIGINT || sig == SIGQUIT) return;
  tstart(T_EXIT, 0, sig, 0);
  exit(0);
}


PRIVATE int dowait()
{
  int stat;

  if (corepid > 0) return cursig = 0;
  while (wait(&stat) != curpid) {};
  if ( WIFEXITED(stat) ) {
        if (WEXITSTATUS(stat) != 127) 
                Printf("child exited with status %d\n", WEXITSTATUS(stat));
        cleanup();
        return 0;
  }
  if ( WIFSIGNALED(stat) ) {
        Printf("child terminated by signal %d\n", WTERMSIG(stat) );
        if (_LOW(stat) & 0x80) Printf("(core dumped)\n");
        cleanup();
        return 0;
  }
  return cursig = WSTOPSIG(stat);
}



PUBLIC void tstart(req, verbose, val, cnt)
int req, verbose, val, cnt;
{
  if (curpid == 0) {
        if (verbose) Printf("No active process.\n");
        return;
  }
  if (req == T_EXIT) {
        ptrace(T_EXIT, curpid, 0L, (long) val);
        dowait();
        return;
  }
  if (cnt == 0) cnt = 1;
  do {
        if (curpnt) {
                if (exebpnt(val)) return;
                if (req == T_RESUME) cnt++;
                val = 0;
        } else {
                ptrace(req, curpid, 0L, (long) val);
                if (dowait() == 0) return;
                val = 0;
                switch (cursig) {
                    case SIGEMT:        /* breakpoint */
                        update();
                        findbpnt(cnt <= 1);
                        break;
                    case SIGTRAP:       /* trace trap? */
                        if (req == T_STEP) break;
                    default:            /* signal */
                        val = cursig;
                        break;
                }
        }
  }
  while (--cnt > 0);
  update();
  if ( verbose ) dasm((long) PC_MEMBER(prc), 1, 1);
}

PRIVATE int run(name, argstr, tflg)
char *name, *argstr;
int tflg;
{
  int procid;
  char *argv[MAXARG], *inf = NULL, *outf = NULL;
  int argc;

  if ((procid = fork()) == 0) {
        /* trace me */
        if (tflg) ptrace(T_OK, 0, 0L, 0L); 
        argv[0] = name;
        for (argc = 1;;) {
                argstr = skip(argstr);
                if (*argstr == '\n' || *argstr == ';') {
                        argv[argc] = 0;
                        if (inf) freopen(inf, "r", stdin);
                        if (outf) freopen(outf, "w", stdout);
                        if (tflg) {
                                execv(name, argv);
                                do_error("execv");
                        } else {
                                execvp(name, argv);
                                do_error("execvp");
                        }
                        exit(127);
                }
                if (*argstr == '<')
                        inf = argstr + 1;
                else if (*argstr == '>')
                        outf = argstr + 1;
                else if (argc == MAXARG) {
                        Printf("Too many arguments.\n");
                        exit(127);
                } else
                        argv[argc++] = argstr;
                while (!isspace(*argstr)) argstr++;
                if (*argstr == '\n') argstr[1] = '\n', argstr[2] = 0;
                *argstr++ = 0;
        }
  }
  if (procid < 0) do_error("Fork failed.\n");
  return procid;
}


PRIVATE void dorun(cmd)
char *cmd;
{
  if (curpid = run(prog, cmd, 1)) {
        if (dowait()) {
                ptrace(T_SETUSER, curpid, BP_OFF, 0L);
                update();
                Printf("Process stopped.\n");
        }
  }
}

/* 
 * backtrace - inspect the stack
 */ 
PRIVATE void backtrace(all)
int all;
{
  unsigned long pc, bp, off, val, obp;

  if (curpid <= 0) {
        Printf("No process.\n");
        return;
  }
  pc = get_reg(curpid,PC_OFF);
  bp = get_reg(curpid,BP_OFF);
  if (bp == 0) {
        Printf("No active frame.\n");
        return;
  }
  errno = 0;
  do {
        symbolic(pc, '(');
        pc = (ptrace(T_GETDATA, curpid, bp + ADDRSIZE, 0L)
              >> SHIFT(ADDRSIZE)) & MASK(ADDRSIZE);
        off = ptrace(T_GETINS, curpid, pc, 0L);
#ifdef  DEBUG
        if(debug)
            Printf("Return address %lx Value %lx\n",pc,off);
#endif
        obp = bp;
        bp += 2 * ADDRSIZE;

        /* Check for various instruction used to restore the stack. 
         * Should gives us the number of arguments.
         * This is obvious dependent on interal features of the 
         * compiler used.
         */ 
        if (ADDQ(off)) off = ADDQ_CNT(off) + bp;
#ifdef __mc68000__
        else if (LEA(off))
                off = LEA_DISP(off) + bp;
#endif
        else if (ADDA(off))
                off = ADDA_CNT(ptrace(T_GETINS, curpid, pc + 2, 0L)) + bp;
#if (CHIP == INTEL)
        else if (INCSP2(off))
                off = bp + 2*INTSIZE;
        else if (POPBX2(off))
                off = bp + 2*INTSIZE;
        else if (POPCX2(off))
                off = bp + 2*INTSIZE;
        else if (POPBX(off))
                off = bp + INTSIZE;
        else if (POPCX(off))
                off = bp + INTSIZE;
#endif
        else
                goto skiplp;

#ifdef DEBUG
        if (debug) 
            Printf("Number of arguments: %d\n",(off-bp)/INTSIZE);
#endif

        for (;;) {
                if (errno) return;
                val = (ptrace(T_GETDATA, curpid, bp, 0L)
                       >> SHIFT(INTSIZE)) & MASK(INTSIZE);
                Printf("0x%0*lx", 2 * INTSIZE, val);
                bp += INTSIZE;
                if (bp >= off) break;
                Printf(",");
        }

skiplp:
        Printf(")\n");
        bp = (long) ( (reg_t) ptrace(T_GETDATA, curpid, obp, 0L) );
#ifdef  DEBUG
        if(debug)
                Printf("Old BP %lx New %lx\n",obp,bp);
#endif
  }
  while (all && (reg_t) bp);
}

PRIVATE void modify(addr, cnt, verbose, size)
long addr;
int cnt, verbose, size;
{
  long curval, off;

  if (curpid == 0) {
        Printf("No active process.\n");
        return;
  }
  curval = ptrace(T_GETDATA, curpid, addr, 0L) & MASK(size);
  do {
        if (cursig == SIGTRAP) cursig = 0;
        if (verbose) {
                off = get_reg(curpid, PC_OFF);
                dasm(off, 1, 0);
        }
        if (curpnt && exebpnt(cursig))
                return;
        else {
                ptrace(T_STEP, curpid, addr, 0L);
                switch (dowait()) {
                    case 0:
                        return;
                    case SIGEMT:
                        update();
                        findbpnt(0);
                        break;
                }
        }
        if (curval != ptrace(T_GETDATA, curpid, addr, 0L) & MASK(size)) {
                Printf("Modification detected\n");
                break;
        }
  }
  while (--cnt);
  update();
  dasm((long) PC_MEMBER(prc), 1, 1);
  return;
}

PRIVATE void display(addr, req)
long addr;
int req;
{
  int count, size, out, shift;
  long val, msk;
  char fmt;

  if (curpid == 0) {
        Printf("No active process\n");
        return;
  }
  if (req == T_GETDATA && seg == T) req = T_GETINS;
  count = strtol(cmd, &cmd, 0);
  if (count == 0) count = 1;
  cmd = skip(cmd);
  if (*cmd == 'i' || *cmd == 'I') {
        dasm(addr, count, *cmd == 'i');
        return;
  }
  if (*cmd == 'y') {
        symbolic(addr, '\n');
        return;
  }
  switch (*cmd++) {
      case 'b': size = sizeof(char);    break;
      case 'h': size = sizeof(short);   break;
      case 'l': size = sizeof(long);    break;
      default:  
        size = sizeof(int);
        --cmd;
        break;
  }
  switch (fmt = *cmd) {
      case 'X':
      case 'D': 
        size = sizeof(long);
        break;
      case 's':
        addr = ptrace(req, curpid, addr, 0L);
        req = T_GETDATA;
      /* Fallthrough */ 
      case 'a': 
      case 'c':
        size = sizeof(char);    
        break;
  }
  out = 0;
  msk = MASK(size);
  shift = SHIFT(size);
  do {
        val = (ptrace(req, curpid, addr, 0L) >> shift) & msk;
        if (out == 0) Printf("\n0x%0*lx: ", 2 * ADDRSIZE,
                       (addr >> SHIFT(ADDRSIZE)) & MASK(ADDRSIZE));
        switch (fmt) {
            case 'c':
                Printf(isprint((int) (UCHAR(val))) ? "   %c " : "\\%03o ",
                                        (int) (UCHAR(val)));
                if (++out == 8) out = 0;
                break;
            case 'u':
                Printf("%12lu ", val);
                if (++out == 4) out = 0;
                break;
            case 'x':
            case 'X':
                Printf("%*lx ", 2 * size, val);
                if (++out == (size == 4 ? 4 : 8)) out = 0;
                break;
            case 'o':
                Printf("%*lo ", 3 * size, val);
                if (++out == (size == 4 ? 4 : 8)) out = 0;
                break;
            case 's':
            case 'a':
                if (val)
                        Printf("%c",val);
                else
                        goto exitlp;
                if (++out == 64) out = 0;
                break;
            default:
            case 'd':
            case 'D':
                Printf("%12ld ", val);
                if (++out == 4) out = 0;
                break;
        }
        addr += size;
  }
  while (--count > 0 || fmt == 's' || fmt == 'a');
exitlp:
  Printf("\n");
}

PRIVATE void fill(addr, req)
long addr;
int req;
{
  int count, size, shift;
  long val, msk, nval;

  if (curpid == 0) {
        Printf("No active process\n");
        return;
  }
  
  if (req == T_GETDATA && seg == T) {
        req = T_GETINS;
        Printf("mdb: warning - modifying text\n");
  }
  count = strtol(cmd, &cmd, 0);
  if ( count == 0 ) count = 1;
  switch (*cmd++) {
      case 'b': size = sizeof(char);    break;
      case 'h': size = sizeof(short);   break;
      case 'l': size = sizeof(long);    break;
      default:
        size = sizeof(int);
        --cmd;
        break;
  }
  shift = SHIFT(size);
  msk = MASK(size);
  cmd = getexp(cmd, &nval, &seg);

#ifdef DEBUG
  if (debug)
        Printf("Filling for Count=%d Size=%d val=%lx\n",count,size,nval);
#endif

  nval <<= shift;
  do {
        val = ptrace(req, curpid, addr, 0L) | (nval & msk);
        val &= (nval | ~msk);
        ptrace(req + 3, curpid, addr, val);
        addr += size;
  }
  while (--count > 0);
}

PRIVATE void not_for_core()
{
  if (corepid > 0)
        mdb_error("Illegal command for 'core' file\n");
}

PRIVATE void command()
{
  char c, *p;
  int i;
  int size;
  int stat;
  long exp, lj, lk;
  struct b_pnt *bp;

  seg = NOSEG;          /* don't restrict segment expressions are in */
  cmdstart = cmd = skip(cmd);
  cmd = getexp(cmd, &exp, &seg);

  if (cmd == cmdstart) {        
        /* Not an expression */
        if (corepid < 0) {      /* default to pc for running processs */
                seg = T;
                exp = PC_MEMBER(prc);
        } else {
                seg = lastseg;
                exp = lastexp;
        }

        /* Is it a help command */
        cmd = skip(cmd+1);
        if (*cmd == '?') {
                help_on(*cmdstart);
                *cmd = '\n';
                return;
        }
        else
                cmd = cmdstart;
  }

  if (seg == NOSEG) seg = T;    /* Absolute becomes Text */
  lastexp = exp;                /* save last expression  */
  lastseg = seg;
#ifdef DEBUG
  if(debug)
        Printf("Current address 0x%0*lx and segment %d\n",  2 * ADDRSIZE, exp, seg);

#endif

  /* Check commands */
  switch (c = *cmd++) {
      case 'r':         /* illegal for 'core' files */
      case 'R':
      case 'k':
      case 'B':
      case 'd':
      case 'D':         not_for_core(); 
                        break;

      case 'b':         /* illegal for 'core' files     */
      case 'c':         /* Otherwise run process first  */
      case 'C':
      case 'm':
      case 'M':
#if     SYSCALLS_SUPPORT
      case 'z':
#endif
      case 'i':
      case 'I':         not_for_core();
                        if (curpid <= 0) dorun("\n");
                        break;

      case 's':         if (curpid <= 0) dorun("\n");
                        break;
        
      default:          break;
  }

  switch (c) {
      case '!':         /* escape to shell */
        if (cmd == cmdstart + 1) {
                cmd = skip(cmd);
                if (*cmd == '\n' || *cmd == ';') {
                        i = run("/bin/sh", "\n", 0);
                } else {
                        for (p = cmd + 1; *p && !isspace(*p); p++) {
                        };
                        *p++ = 0;
                        i = run(cmd, *p ? p : "\n", 0);
                }
                if (i > 0) while (wait(&stat) != i) {};
                break;
        }
        if (corepid > 0) longjmp(mainlp, 0);
        break;
      case 'T':         /* top line of backtrace */
        backtrace(0);
        break;
      case 't':         /* back trace */
        backtrace(1);
        break;
      case '/':         /* print variable value */
        display(exp, T_GETDATA);
        break;
      case 'x':         /* print registers and instruction */
        if (disp_regs()) break;
        /* FALLTHROUGH */
      case 'X':         /* print instruction - X n [, n] */
        lj = strtol(cmd, &cmd, 0);
        lk = 0;
        if (*cmd != '\n') 
                lk = strtol(++cmd, &cmd, 0);
        if (curpid > 0)
                dasm(exp + lk, lj ? lj : 1, 1);
        else
                Printf("No active process.\n");
        break;
      case 'R':         /* run program with no args */
      case 'r':         /* run program with args (possibly defaulted) */
        tstart(T_EXIT, 0, 0, 0);
        if (c == 'r') {
                cmd = skip(cmd);
                if (*cmd == '\n' || *cmd == ';')
                        cmd = sbuf;
                else
                        strcpy(sbuf, cmd);
        } else {
                cmd = "\n";
        }
        dorun(cmd);
        break;
      case 'c':         /* continue program - ignore signal */
        cursig = 0;
      case 'C':         /* continue program - handle signal */
        i = 0;
        if (seg == T && curpnt == 0 && cmd != cmdstart + 1) {
                breakpt(exp, "\n");
                curpnt = b_head;
                ptrace(T_SETINS, curpid, curpnt->addr, curpnt->oldval);
                i = 1;
        }
        tstart(T_RESUME, 1, cursig, (int) strtol(cmd, &cmd, 0));
        /* remove temporary bp */
        if (i) freepnt(b_head);
        if (cursig == SIGEMT) return;
        if (curpid) Printf("Process stopped by signal %d\n", cursig);
        break;
      case 'i':         /* single step - ignore signal */
        tstart(T_STEP, 1, 0, (int) strtol(cmd, &cmd, 0));
        break;
      case 'I':         /* single step - handle signal */
        tstart(T_STEP, 1, cursig, (int) strtol(cmd, &cmd, 0));
        break;
      case 'm':         /* single step until location modified */
      case 'M':         /* single step until location modified - verbose */
        cmd = skip(cmd);
        switch (*cmd++) {
            case 'b':   size = sizeof(char);    break;
            case 'h':   size = sizeof(short);   break;
            case 'l':   size = sizeof(long);    break;
            default:
                size = sizeof(int);
                --cmd;
                break;
        }
        modify(exp, (int) strtol(cmd, &cmd, 0), c == 'M', size);
        break;
      case 'k':         /* kill current program */
        tstart(T_EXIT, 1, 0, 0);
        break;
      case 'b':         /* set a breakpoint at the given line */
#ifdef  MINIX_PC
        if (seg != T || exp > end_addr ) {
#else
        if (seg != T || exp < st_addr || exp > et_addr ) {
#endif  
                Printf("Address not in text space.\n");
                return;
        }
        breakpt(exp, skip(cmd));
        cmd = "\n";
        return;
      case 'B':         /* print list of currently active breakpoints */
        for (i = 1, bp = b_head; bp; bp = bp->nxt, i++) {
                Printf("%2d: ", i);
                symbolic((long) bp->addr, '\t');
                Printf("(0x%lx)\t- %s", bp->addr, bp->cmd);
        }
        break;
      case 'd':         /* delete breakpoint */
        if (seg == T) {
                for (bp = b_head; bp && bp->addr != exp; bp = bp->nxt);
                if (bp) {
                        freepnt(bp);
                        break;
                }
        }
        Printf("No such breakpoint.\n");
        break;
      case 'D':         /* delete all breakpoints */
        while (b_head) freepnt(b_head);
        break;
      case 's':
        dump_stack( strtol(cmd, &cmd, 0) );
        break;
      case 'P':
        paging = !paging;
        if (paging) Printf("Paging is ON\n");
        break;
      case 'l':
      case 'L':
        logging(c,skip(cmd));
        break;
#if     SYSCALLS_SUPPORT
      case 'z':
        start_syscall( strtol(cmd, &cmd, 0) );
        if ( syscalls ) 
                Printf("Break point set - use the 'c n' command\n");
        break;
#endif
      case 'q':         /* quit */
        tstart(T_EXIT, 0, 0, 0);
        logging(c,cmd);
      case 'Q':
        exit(0);        
        break;
      case '\n':
      case ';':
        if (isdigit(*cmdstart))
                symbolic(exp, '\n');
        else
                Printf("0x%0*lx\n", 2 * ADDRSIZE, exp);
        --cmd;
        break;
#ifdef  DEBUG
      case 'v':         /* toggle debug */
        debug = !debug;
        if (debug) Printf("Debug flag ON\n");
        break;
#endif
      case 'e':         /* list symbols */
        listsym(cmd);
        break;
      case 'y':         /* print mapping */
        prtmap();
        break;
      case '?':         /* print help */
        help_page();
        break;
      case 'V':         /* print version info */
        version_info();
        break;
      case '@':         /* command file  */
        cmd = skip(cmd);
        openin(cmd);
        *cmd = '\n';
        return;
      case '#':         /* set register or variable */
        cmd = skip(cmd + 1);
        if (*cmd == '$') {
                cmd++;
                i = reg_addr(cmd); 
                set_reg(curpid, i, strtol(cmd+2, &cmd, 0) );
                update();
                break;
        }
        cmd = getexp(cmd, &exp, &seg);
        fill(exp, T_GETDATA);
        break;
      default:  
        help_page();
        break;
  }
  while (*cmd != '\n' && *cmd != ';') ++cmd;
  if (*cmd == ';') cmd = skip(cmd + 1);
}

PUBLIC void mdb_error(s)
char *s;
{
  Printf("%s",s);
  longjmp(mainlp, 0);
}

PUBLIC void main(argc, argv)
int argc;
char *argv[];
{
  int i, c;
  char *p, *q, *r;
  int opt_c = FALSE;    /* load core file */
  int opt_f = FALSE;    /* load object file */
  int opt_l = FALSE;    /* log to file */
  int opt_L = FALSE;    /* log to file and screen */


  prc = (struct proc *) lbuf;
  strcpy(sbuf, "\n");
  corepid = -1; /* set to indicate none */
  prog = p = q = r = NULL;

  if ( argc == 1 )
  {
        help_page();
        exit(0);
  }

  /* Possible combinations of arguments:
   * A single file name:
   *    If the name is 'core', the coreonly flag is set.
   * The -c flag: examine a core file.
   *    One filename is required with this flag.
   * The -f flag: examine an object file.
   *    One file name is required with this flag.
   * The -L or -l flag: write to a log file.
   *    One file name is required with these flags.
   * The -x flag: turn on debugging.
   *    Used for debugging, and followed by an integer
   *    argument which is the debugging level.
   *
   * If any files remain on the argument list, the first
   * file is an executable, and the second a core file.
   * If any filename starts with '@' it is assumed to
   * to be a command file.  Only one command file is
   * loaded.
   */

  /* check for default file name and fake out getopt */
  if (strcmp(argv[1], "core") == 0) {
        for (i = argc ; i > 1 ; i--)
                argv[i] = argv[i - 1];
        argv[i] = "-c";
        argc++;
  }

  /* parse options */
  opterr = 0;
  while ((i = getopt(argc, argv, "c:f:L:l:x:")) != EOF) {
        switch (i & 0377) {
        case 'c':               /* examine a core file */
                if (opt_c == TRUE || opt_f == TRUE) {
                        help_page();
                        exit(1);
                }
                p = optarg;
                opt_c = TRUE;
                break;
        case 'f':               /* examine an object file */
                if (opt_c == TRUE || opt_f == TRUE) {
                        help_page();
                        exit(1);
                }
                p = optarg;
                opt_f = TRUE;
                break;
        case 'l':               /* start logging */
                if (opt_l == TRUE || opt_L == TRUE) {
                        help_page();
                        exit(1);
                }
                opt_l = TRUE;
                logging(i, optarg);
                break;
        case 'L':               /* start logging */
                if (opt_l == TRUE || opt_L == TRUE) {
                        help_page();
                        exit(1);
                }
                opt_L = TRUE;
                logging(i, optarg);
                break;
#ifdef DEBUG
        case 'x':               /* set debug level */
                debug = atoi(optarg);
                break;
#endif
        case '?':               /* default arguments arrive here */
        default:
                help_page();
                exit(1);
        }
  }

  /* can't cope without filenames */
  if (!opt_c && !opt_f && optind >= argc) {
        help_page();
        exit(1);
  }

  /* any remaining arguments are (optional) file names */
  for (i = optind ; i < argc ; i++) {
        if (*argv[i] == '@') {                  /* command file */
                if (r == NULL) r = argv[i] + 1;
        }
        /* you can't combine a -c or -f object file and a core file */
        else if (!opt_c && !opt_f && p == NULL) p = argv[i];
        else if (q == NULL) q = argv[i];        /* core file */
  }

  /* initialise stuff - fairly tricky logic */
  coreonly = opt_c;
  fileonly = opt_f;
  /* when examining files, prog == NULL */
  if (!opt_c && !opt_f) {
        prog = p;
        syminit(prog);
  }

  /* file_init is called for non-core files. 
   * It is very similar to core_init. It opens the file and set
   * various pointers so that we can read it using the same routines
   * as a core file. 
   * NB: Currently there is no special provision to handle object files.
   */

  /* A comment from Will Rose:
   * It would be nice to have
   * symbol tables available when reading a core
   * or a.out, either as part of the executable or
   * as a separate file.
   * At least three separate types of file structure
   * may be used by mdb - core files, a.out files, and
   * object files (which may have several flavours).
   * A set of routines is needed for each type, with
   * a function switch table initialised  when mdb is
   * started up.
   */

  if (opt_c) lastexp = core_init(p);
  if (opt_f) lastexp = file_init(p);
  if (q != NULL) lastexp = core_init(q);
  if (r != NULL) openin(r);
  for (i = 1; i < _NSIG; i++) signal(i, catch);

  setjmp(mainlp);

  while (get_cmd( cbuf, MAXLINE ) != NULL) {
        if (strlen(cbuf) == sizeof(cbuf) - 1) {
                Printf("Command line too long.\n");
                continue;
        }
        cmd = cbuf;
        command();
        while (*cmd != '\n') command();
  }
  tstart(T_EXIT, 0, 0, 0);
  exit(0);
}

---