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/*
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 * Simple example of use of vm86: launch a basic .com DOS executable
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 */
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#include <inttypes.h>
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#include <unistd.h>
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#include <fcntl.h>
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#include <sys/mman.h>
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#include <signal.h>
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#include <linux/unistd.h>
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#include <asm/vm86.h>
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//#define SIGTEST
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#undef __syscall_return
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#define __syscall_return(type, res) \
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do { \
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        return (type) (res); \
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} while (0)
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_syscall2(int, vm86, int, func, struct vm86plus_struct *, v86)
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#define COM_BASE_ADDR    0x10100
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void usage(void)
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{
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    printf("runcom version 0.1 (c) 2003 Fabrice Bellard\n"
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           "usage: runcom file.com\n"
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           "VM86 Run simple .com DOS executables (linux vm86 test mode)\n");
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    exit(1);
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}
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static inline void set_bit(uint8_t *a, unsigned int bit)
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{
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    a[bit / 8] |= (1 << (bit % 8));
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}
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static inline uint8_t *seg_to_linear(unsigned int seg, unsigned int reg)
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{
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    return (uint8_t *)((seg << 4) + (reg & 0xffff));
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}
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static inline void pushw(struct vm86_regs *r, int val)
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{
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    r->esp = (r->esp & ~0xffff) | ((r->esp - 2) & 0xffff);
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    *(uint16_t *)seg_to_linear(r->ss, r->esp) = val;
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}
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void dump_regs(struct vm86_regs *r)
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{
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    fprintf(stderr,
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            "EAX=%08lx EBX=%08lx ECX=%08lx EDX=%08lx\n"
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            "ESI=%08lx EDI=%08lx EBP=%08lx ESP=%08lx\n"
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            "EIP=%08lx EFL=%08lx\n"
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            "CS=%04x DS=%04x ES=%04x SS=%04x FS=%04x GS=%04x\n",
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            r->eax, r->ebx, r->ecx, r->edx, r->esi, r->edi, r->ebp, r->esp,
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            r->eip, r->eflags,
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            r->cs, r->ds, r->es, r->ss, r->fs, r->gs);
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}
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#ifdef SIGTEST
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void alarm_handler(int sig)
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{
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    fprintf(stderr, "alarm signal=%d\n", sig);
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    alarm(1);
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}
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#endif
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int main(int argc, char **argv)
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{
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    uint8_t *vm86_mem;
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    const char *filename;
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    int fd, ret, seg;
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    struct vm86plus_struct ctx;
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    struct vm86_regs *r;
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    if (argc != 2)
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        usage();
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    filename = argv[1];
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    vm86_mem = mmap((void *)0x00000000, 0x110000,
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                    PROT_WRITE | PROT_READ | PROT_EXEC,
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                    MAP_FIXED | MAP_ANON | MAP_PRIVATE, -1, 0);
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    if (vm86_mem == MAP_FAILED) {
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        perror("mmap");
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        exit(1);
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    }
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#ifdef SIGTEST
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    {
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        struct sigaction act;
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        act.sa_handler = alarm_handler;
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        sigemptyset(&act.sa_mask);
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        act.sa_flags = 0;
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        sigaction(SIGALRM, &act, NULL);
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        alarm(1);
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    }
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#endif
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    /* load the MSDOS .com executable */
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    fd = open(filename, O_RDONLY);
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    if (fd < 0) {
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        perror(filename);
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        exit(1);
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    }
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    ret = read(fd, vm86_mem + COM_BASE_ADDR, 65536 - 256);
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    if (ret < 0) {
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        perror("read");
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        exit(1);
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    }
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    close(fd);
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    memset(&ctx, 0, sizeof(ctx));
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    /* init basic registers */
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    r = &ctx.regs;
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    r->eip = 0x100;
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    r->esp = 0xfffe;
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    seg = (COM_BASE_ADDR - 0x100) >> 4;
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    r->cs = seg;
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    r->ss = seg;
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    r->ds = seg;
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    r->es = seg;
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    r->fs = seg;
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    r->gs = seg;
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    r->eflags = VIF_MASK;
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    /* put return code */
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    set_bit((uint8_t *)&ctx.int_revectored, 0x21);
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    *seg_to_linear(r->cs, 0) = 0xb4; /* mov ah, $0 */
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    *seg_to_linear(r->cs, 1) = 0x00;
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    *seg_to_linear(r->cs, 2) = 0xcd; /* int $0x21 */
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    *seg_to_linear(r->cs, 3) = 0x21;
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    pushw(&ctx.regs, 0x0000);
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    /* the value of these registers seem to be assumed by pi_10.com */
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    r->esi = 0x100;
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    r->ecx = 0xff;
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    r->ebp = 0x0900;
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    r->edi = 0xfffe;
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    for(;;) {
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        ret = vm86(VM86_ENTER, &ctx);
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        switch(VM86_TYPE(ret)) {
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        case VM86_INTx:
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            {
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                int int_num, ah;
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                int_num = VM86_ARG(ret);
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                if (int_num != 0x21)
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                    goto unknown_int;
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                ah = (r->eax >> 8) & 0xff;
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                switch(ah) {
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                case 0x00: /* exit */
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                    exit(0);
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                case 0x02: /* write char */
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                    {
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                        uint8_t c = r->edx;
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                        write(1, &c, 1);
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                    }
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                    break;
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                case 0x09: /* write string */
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                    {
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                        uint8_t c;
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                        for(;;) {
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                            c = *seg_to_linear(r->ds, r->edx);
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                            if (c == '$')
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                                break;
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                            write(1, &c, 1);
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                        }
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                        r->eax = (r->eax & ~0xff) | '$';
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                    }
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                    break;
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                default:
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                unknown_int:
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                    fprintf(stderr, "unsupported int 0x%02x\n", int_num);
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                    dump_regs(&ctx.regs);
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                    //                    exit(1);
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                }
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            }
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            break;
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        case VM86_SIGNAL:
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            /* a signal came, we just ignore that */
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            break;
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        case VM86_STI:
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            break;
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        default:
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            fprintf(stderr, "unhandled vm86 return code (0x%x)\n", ret);
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            dump_regs(&ctx.regs);
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            exit(1);
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        }
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    }
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}