dismain.c

操作系统源代码

}/* * * * * * * * * * * END OF prolog() * * * * * * * * * * */

 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  *                                                         *
  * This function is  responsible  for  disassembly  of the *
  * object file's text segment.                             *
  *                                                         *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

static void
distext()

{/* * * * * * * * * * START OF  distext() * * * * * * * * * */

   char *c;
   register int j;
   register void (*f)();

   for (j = 0; j < (int)(HDR.a_hdrlen); ++j)
      getchar();

   printf("| %s, %s\n\n",PRG,release);

   printf("| @(");

   printf("#)\tDisassembly of %s",IFILE);

   if (symptr < 0)
      printf(" (no symbols)\n\n");
   else
      printf("\n\n");

   if (HDR.a_flags & A_EXEC)
      printf("| File is executable\n\n");

   if (HDR.a_flags & A_SEP)
      {
      printf("| File has split I/D space, and may have\n");
      printf("| extraneous instructions in text segment\n\n");
      }

   prolog();

   printf("\t.text\t\t\t| loc = %05.5lx, size = %05.5lx\n\n",
    PC,HDR.a_text);

   segflg = 0;

   for (PC = 0L; PC < HDR.a_text; ++PC)
      {
      j = getchar() & 0xff;
      if ((j == 0) && ((PC + 1L) == HDR.a_text))
         {
         ++PC;
         break;
         }
      if ((c = getlab(N_TEXT)) != NULL)
         printf("%s",c);
      f = optab[j].func;
      (*f)(j);
      }

}/* * * * * * * * * *  END OF  distext()  * * * * * * * * * */

 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  *                                                         *
  * This  function  handles the object file's data segment. *
  * There is no good way to disassemble a data segment, be- *
  * cause it is  impossible  to tell,  from the object code *
  * alone,  what each data byte refers to.  If it refers to *
  * an external symbol,  the reference can be resolved from *
  * the relocation table, if there is one.  However,  if it *
  * refers to a static symbol,  it cannot be  distinguished *
  * from numeric, character, or other pointer data. In some *
  * cases,  one might make a semi-educated  guess as to the *
  * nature of the data,  but such  guesses  are  inherently *
  * haphazard,  and they are  bound to be wrong a good por- *
  * tion of the time.  Consequently,  the data  segment  is *
  * disassembled  as a byte  stream,  which will satisfy no *
  * one but which, at least, will never mislead anyone.     *
  *                                                         *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

static void
disdata()

{/* * * * * * * * * * START OF  disdata() * * * * * * * * * */

   register char *c;
   register int j;
   unsigned long end;

   putchar('\n');

   if (HDR.a_flags & A_SEP)
      {
      PC = 0L;
      end = HDR.a_data;
      }
   else
      end = HDR.a_text + HDR.a_data;

   printf("\t.data\t\t\t| loc = %05.5lx, size = %05.5lx\n\n",
    PC,HDR.a_data);

   segflg = 0;

   for (objptr = 0, zcount = 0L; PC < end; ++PC)
      {
      if ((c = getlab(N_DATA)) != NULL)
         {
         objdump(c);
         printf("%s",c);
         }
      if (objptr >= OBJMAX)
         if (objdump(NULL) && (symptr < 0))
            printf("D%05.5lx:",PC);
      j = getchar() & 0xff;
      objbuf[objptr++] = j;
      }

   objdump("");

}/* * * * * * * * * *  END OF  disdata()  * * * * * * * * * */

 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  *                                                         *
  * This  function  handles the object  file's bss segment. *
  * Disassembly of the bss segment is easy,  because every- *
  * thing in it is zero by definition.                      *
  *                                                         *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

static void disbss()

{/* * * * * * * * * *  START OF disbss()  * * * * * * * * * */

   register int j;
   register char *c;
   unsigned long beg, end;

   putchar('\n');

   if (HDR.a_flags & A_SEP)
      end = HDR.a_data + HDR.a_bss;
   else
      end = HDR.a_text + HDR.a_data + HDR.a_bss;

   printf("\t.bss\t\t\t| loc = %05.5lx, size = %05.5lx\n\n",
    PC,HDR.a_bss);

   segflg = 0;

   for (beg = PC; PC < end; ++PC)
      if ((c = getlab(N_BSS)) != NULL)
         {
         if (PC > beg)
            {
            zdump(beg);
            beg = PC;
            }
         printf("%s",c);
         }

   if (PC > beg)
      zdump(beg);

}/* * * * * * * * * * * END OF disbss() * * * * * * * * * * */

 /* * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
  *                                                         *
  * This is the program  entry  point.  The command line is *
  * searched for an input file name, which must be present. *
  * An optional output file name is also permitted; if none *
  * is found, standard output is the default.  One command- *
  * line option is available:  "-o",  which causes the pro- *
  * gram to include  object code in comments along with its *
  * mnemonic output.                                        *
  *                                                         *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

void
main(argc,argv)

   int argc;                  /* Command-line args from OS  */
   register char **argv;

{/* * * * * * * * * * * START OF main() * * * * * * * * * * */

   char a[1024];
   register int fd;
   long taboff, tabnum;
   long reloff, relnum;

   PRG = invoker(*argv);

   while (*++argv != NULL)    /* Process command-line args  */
      if (**argv == '-')
         switch (*++*argv)
            {
            case 'o' :
               if (*++*argv)
                  usage(PRG);
               else
                  ++objflg;
               break;
            default :
               usage(PRG);
            }
      else
         if (IFILE == NULL)
            IFILE = *argv;
         else if (OFILE == NULL)
            OFILE = *argv;
         else
            usage(PRG);

   if (IFILE == NULL)
      usage(PRG);
   else
      if ((fd = open(IFILE,0)) < 0)
         {
         sprintf(a,"can't access input file %s",IFILE);
         fatal(PRG,a);
         }

   if (OFILE != NULL)
      if (freopen(OFILE,"w",stdout) == NULL)
         {
         sprintf(a,"can't open output file %s",OFILE);
         fatal(PRG,a);
         }

   if ( ! cpuid )
      fprintf(stderr,"\07%s: warning: host/cpu clash\n",PRG);

   read(fd, (char *) &HDR,sizeof(struct exec));

   if (BADMAG(HDR))
      {
      sprintf(a,"input file %s not in object format",IFILE);
      fatal(PRG,a);
      }

   if (HDR.a_cpu != A_I8086)
      {
      sprintf(a,"%s is not an 8086/8088 object file",IFILE);
      fatal(PRG,a);
      }

   if (HDR.a_hdrlen <= A_MINHDR)
      HDR.a_trsize = HDR.a_drsize = 0L;
      HDR.a_tbase = HDR.a_dbase = 0L;
/*   AST emergency patch
      HDR.a_lnums = HDR.a_toffs = 0L;
*/

   reloff = HDR.a_text        /* Compute reloc data offset  */
          + HDR.a_data
          + (long)(HDR.a_hdrlen);

   relnum =
      (HDR.a_trsize + HDR.a_drsize) / sizeof(struct reloc);

   taboff = reloff            /* Compute name table offset  */
          + HDR.a_trsize
          + HDR.a_drsize;

   tabnum = HDR.a_syms / sizeof(struct nlist);

   if (relnum > MAXSYM)
      fatal(PRG,"reloc table overflow");

   if (tabnum > MAXSYM)
      fatal(PRG,"symbol table overflow");

   if (relnum)                            /* Get reloc data */
      if (lseek(fd,reloff,0) != reloff)
         fatal(PRG,"lseek error");
      else
         {
         for (relptr = 0; relptr < relnum; ++relptr)
            read(fd, (char *) &relo[relptr],sizeof(struct reloc));
         relptr--;
         }

   if (tabnum)                            /* Read in symtab */
      if (lseek(fd,taboff,0) != taboff)
         fatal(PRG,"lseek error");
      else
         {
         for (symptr = 0; symptr < tabnum; ++symptr)
            read(fd, (char *) &symtab[symptr],sizeof(struct nlist));
         symptr--;
         }
   else
      fprintf(stderr,"\07%s: warning: no symbols\n",PRG);

   close(fd);

   if (freopen(IFILE,"r",stdin) == NULL)
      {
      sprintf(a,"can't reopen input file %s",IFILE);
      fatal(PRG,a);
      }

   distext();

   disdata();

   disbss();

   exit(0);

}/* * * * * * * * * * *  END OF main()  * * * * * * * * * * */