Archipelago » qemu

/*

 * Simple example of use of vm86: launch a basic .com DOS executable

 */

#include <stdlib.h>

#include <stdio.h>

#include <string.h>

#include <inttypes.h>

#include <unistd.h>

#include <fcntl.h>

#include <sys/mman.h>

#include <signal.h>

#include <linux/unistd.h>

#include <asm/vm86.h>

extern int vm86 (unsigned long int subfunction,

                 struct vm86plus_struct *info);

#define VIF_MASK                0x00080000

//#define SIGTEST

#define COM_BASE_ADDR    0x10100

static void usage(void)

{

    printf("runcom version 0.1 (c) 2003 Fabrice Bellard\n"

           "usage: runcom file.com\n"

           "VM86 Run simple .com DOS executables (linux vm86 test mode)\n");

    exit(1);

}

static inline void set_bit(uint8_t *a, unsigned int bit)

{

    a[bit / 8] |= (1 << (bit % 8));

}

static inline uint8_t *seg_to_linear(unsigned int seg, unsigned int reg)

{

    return (uint8_t *)((seg << 4) + (reg & 0xffff));

}

static inline void pushw(struct vm86_regs *r, int val)

{

    r->esp = (r->esp & ~0xffff) | ((r->esp - 2) & 0xffff);

    *(uint16_t *)seg_to_linear(r->ss, r->esp) = val;

}

void dump_regs(struct vm86_regs *r)

{

    fprintf(stderr,

            "EAX=%08lx EBX=%08lx ECX=%08lx EDX=%08lx\n"

            "ESI=%08lx EDI=%08lx EBP=%08lx ESP=%08lx\n"

            "EIP=%08lx EFL=%08lx\n"

            "CS=%04x DS=%04x ES=%04x SS=%04x FS=%04x GS=%04x\n",

            r->eax, r->ebx, r->ecx, r->edx, r->esi, r->edi, r->ebp, r->esp,

            r->eip, r->eflags,

            r->cs, r->ds, r->es, r->ss, r->fs, r->gs);

}

#ifdef SIGTEST

void alarm_handler(int sig)

{

    fprintf(stderr, "alarm signal=%d\n", sig);

    alarm(1);

}

#endif

int main(int argc, char **argv)

{

    uint8_t *vm86_mem;

    const char *filename;

    int fd, ret, seg;

    struct vm86plus_struct ctx;

    struct vm86_regs *r;

    if (argc != 2)

        usage();

    filename = argv[1];

    vm86_mem = mmap((void *)0x00000000, 0x110000,

                    PROT_WRITE | PROT_READ | PROT_EXEC,

                    MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);

    if (vm86_mem == MAP_FAILED) {

        perror("mmap");

        exit(1);

    }

#ifdef SIGTEST

    {

        struct sigaction act;

        act.sa_handler = alarm_handler;

        sigemptyset(&act.sa_mask);

        act.sa_flags = 0;

        sigaction(SIGALRM, &act, NULL);

        alarm(1);

    }

#endif

    /* load the MSDOS .com executable */

    fd = open(filename, O_RDONLY);

    if (fd < 0) {

        perror(filename);

        exit(1);

    }

    ret = read(fd, vm86_mem + COM_BASE_ADDR, 65536 - 256);

    if (ret < 0) {

        perror("read");

        exit(1);

    }

    close(fd);

    memset(&ctx, 0, sizeof(ctx));

    /* init basic registers */

    r = &ctx.regs;

    r->eip = 0x100;

    r->esp = 0xfffe;

    seg = (COM_BASE_ADDR - 0x100) >> 4;

    r->cs = seg;

    r->ss = seg;

    r->ds = seg;

    r->es = seg;

    r->fs = seg;

    r->gs = seg;

    r->eflags = VIF_MASK;

    /* put return code */

    set_bit((uint8_t *)&ctx.int_revectored, 0x21);

    *seg_to_linear(r->cs, 0) = 0xb4; /* mov ah, $0 */

    *seg_to_linear(r->cs, 1) = 0x00;

    *seg_to_linear(r->cs, 2) = 0xcd; /* int $0x21 */

    *seg_to_linear(r->cs, 3) = 0x21;

    pushw(&ctx.regs, 0x0000);

    /* the value of these registers seem to be assumed by pi_10.com */

    r->esi = 0x100;

    r->ecx = 0xff;

    r->ebp = 0x0900;

    r->edi = 0xfffe;

    for(;;) {

        ret = vm86(VM86_ENTER, &ctx);

        switch(VM86_TYPE(ret)) {

        case VM86_INTx:

            {

                int int_num, ah;

                int_num = VM86_ARG(ret);

                if (int_num != 0x21)

                    goto unknown_int;

                ah = (r->eax >> 8) & 0xff;

                switch(ah) {

                case 0x00: /* exit */

                    exit(0);

                case 0x02: /* write char */

                    {

                        uint8_t c = r->edx;

                        write(1, &c, 1);

                    }

                    break;

                case 0x09: /* write string */

                    {

                        uint8_t c;

                        for(;;) {

                            c = *seg_to_linear(r->ds, r->edx);

                            if (c == '$')

                                break;

                            write(1, &c, 1);

                        }

                        r->eax = (r->eax & ~0xff) | '$';

                    }

                    break;

                default:

                unknown_int:

                    fprintf(stderr, "unsupported int 0x%02x\n", int_num);

                    dump_regs(&ctx.regs);

                    //                    exit(1);

                }

            }

            break;

        case VM86_SIGNAL:

            /* a signal came, we just ignore that */

            break;

        case VM86_STI:

            break;

        default:

            fprintf(stderr, "unhandled vm86 return code (0x%x)\n", ret);

            dump_regs(&ctx.regs);

            exit(1);

        }

    }

}