tests/runcom.c

   1 /*
   2  * Simple example of use of vm86: launch a basic .com DOS executable
   3  */
   4 #include <stdlib.h>
   5 #include <stdio.h>
   6 #include <string.h>
   7 #include <inttypes.h>
   8 #include <unistd.h>
   9 #include <fcntl.h>
  10 #include <sys/mman.h>
  11 #include <signal.h>
  12
  13 #include <linux/unistd.h>
  14 #include <asm/vm86.h>
  15
  16 extern int vm86 (unsigned long int subfunction,
  17                  struct vm86plus_struct *info);
  18
  19 #define VIF_MASK                0x00080000
  20
  21 //#define SIGTEST
  22
  23 #define COM_BASE_ADDR    0x10100
  24
  25 static void usage(void)
  26 {
  27     printf("runcom version 0.1 (c) 2003 Fabrice Bellard\n"
  28            "usage: runcom file.com\n"
  29            "VM86 Run simple .com DOS executables (linux vm86 test mode)\n");
  30     exit(1);
  31 }
  32
  33 static inline void set_bit(uint8_t *a, unsigned int bit)
  34 {
  35     a[bit / 8] |= (1 << (bit % 8));
  36 }
  37
  38 static inline uint8_t *seg_to_linear(unsigned int seg, unsigned int reg)
  39 {
  40     return (uint8_t *)((seg << 4) + (reg & 0xffff));
  41 }
  42
  43 static inline void pushw(struct vm86_regs *r, int val)
  44 {
  45     r->esp = (r->esp & ~0xffff) | ((r->esp - 2) & 0xffff);
  46     *(uint16_t *)seg_to_linear(r->ss, r->esp) = val;
  47 }
  48
  49 void dump_regs(struct vm86_regs *r)
  50 {
  51     fprintf(stderr,
  52             "EAX=%08lx EBX=%08lx ECX=%08lx EDX=%08lx\n"
  53             "ESI=%08lx EDI=%08lx EBP=%08lx ESP=%08lx\n"
  54             "EIP=%08lx EFL=%08lx\n"
  55             "CS=%04x DS=%04x ES=%04x SS=%04x FS=%04x GS=%04x\n",
  56             r->eax, r->ebx, r->ecx, r->edx, r->esi, r->edi, r->ebp, r->esp,
  57             r->eip, r->eflags,
  58             r->cs, r->ds, r->es, r->ss, r->fs, r->gs);
  59 }
  60
  61 #ifdef SIGTEST
  62 void alarm_handler(int sig)
  63 {
  64     fprintf(stderr, "alarm signal=%d\n", sig);
  65     alarm(1);
  66 }
  67 #endif
  68
  69 int main(int argc, char **argv)
  70 {
  71     uint8_t *vm86_mem;
  72     const char *filename;
  73     int fd, ret, seg;
  74     struct vm86plus_struct ctx;
  75     struct vm86_regs *r;
  76
  77     if (argc != 2)
  78         usage();
  79     filename = argv[1];
  80
  81     vm86_mem = mmap((void *)0x00000000, 0x110000,
  82                     PROT_WRITE | PROT_READ | PROT_EXEC,
  83                     MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
  84     if (vm86_mem == MAP_FAILED) {
  85         perror("mmap");
  86         exit(1);
  87     }
  88 #ifdef SIGTEST
  89     {
  90         struct sigaction act;
  91
  92         act.sa_handler = alarm_handler;
  93         sigemptyset(&act.sa_mask);
  94         act.sa_flags = 0;
  95         sigaction(SIGALRM, &act, NULL);
  96         alarm(1);
  97     }
  98 #endif
  99
 100     /* load the MSDOS .com executable */
 101     fd = open(filename, O_RDONLY);
 102     if (fd < 0) {
 103         perror(filename);
 104         exit(1);
 105     }
 106     ret = read(fd, vm86_mem + COM_BASE_ADDR, 65536 - 256);
 107     if (ret < 0) {
 108         perror("read");
 109         exit(1);
 110     }
 111     close(fd);
 112
 113     memset(&ctx, 0, sizeof(ctx));
 114     /* init basic registers */
 115     r = &ctx.regs;
 116     r->eip = 0x100;
 117     r->esp = 0xfffe;
 118     seg = (COM_BASE_ADDR - 0x100) >> 4;
 119     r->cs = seg;
 120     r->ss = seg;
 121     r->ds = seg;
 122     r->es = seg;
 123     r->fs = seg;
 124     r->gs = seg;
 125     r->eflags = VIF_MASK;
 126
 127     /* put return code */
 128     set_bit((uint8_t *)&ctx.int_revectored, 0x21);
 129     *seg_to_linear(r->cs, 0) = 0xb4; /* mov ah, $0 */
 130     *seg_to_linear(r->cs, 1) = 0x00;
 131     *seg_to_linear(r->cs, 2) = 0xcd; /* int $0x21 */
 132     *seg_to_linear(r->cs, 3) = 0x21;
 133     pushw(&ctx.regs, 0x0000);
 134
 135     /* the value of these registers seem to be assumed by pi_10.com */
 136     r->esi = 0x100;
 137     r->ecx = 0xff;
 138     r->ebp = 0x0900;
 139     r->edi = 0xfffe;
 140
 141     for(;;) {
 142         ret = vm86(VM86_ENTER, &ctx);
 143         switch(VM86_TYPE(ret)) {
 144         case VM86_INTx:
 145             {
 146                 int int_num, ah;
 147
 148                 int_num = VM86_ARG(ret);
 149                 if (int_num != 0x21)
 150                     goto unknown_int;
 151                 ah = (r->eax >> 8) & 0xff;
 152                 switch(ah) {
 153                 case 0x00: /* exit */
 154                     exit(0);
 155                 case 0x02: /* write char */
 156                     {
 157                         uint8_t c = r->edx;
 158                         write(1, &c, 1);
 159                     }
 160                     break;
 161                 case 0x09: /* write string */
 162                     {
 163                         uint8_t c;
 164                         for(;;) {
 165                             c = *seg_to_linear(r->ds, r->edx);
 166                             if (c == '$')
 167                                 break;
 168                             write(1, &c, 1);
 169                         }
 170                         r->eax = (r->eax & ~0xff) | '$';
 171                     }
 172                     break;
 173                 default:
 174                 unknown_int:
 175                     fprintf(stderr, "unsupported int 0x%02x\n", int_num);
 176                     dump_regs(&ctx.regs);
 177                     //                    exit(1);
 178                 }
 179             }
 180             break;
 181         case VM86_SIGNAL:
 182             /* a signal came, we just ignore that */
 183             break;
 184         case VM86_STI:
 185             break;
 186         default:
 187             fprintf(stderr, "unhandled vm86 return code (0x%x)\n", ret);
 188             dump_regs(&ctx.regs);
 189             exit(1);
 190         }
 191     }
 192 }