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* Simple example of use of vm86: launch a basic .com DOS executable
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#include <linux/unistd.h>
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#undef __syscall_return
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#define __syscall_return(type, res) \
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return (type) (res); \
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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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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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static inline void set_bit(uint8_t *a, unsigned int bit)
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a[bit / 8] |= (1 << (bit % 8));
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static inline uint8_t *seg_to_linear(unsigned int seg, unsigned int reg)
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return (uint8_t *)((seg << 4) + (reg & 0xffff));
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static inline void pushw(struct vm86_regs *r, int val)
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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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void dump_regs(struct vm86_regs *r)
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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->cs, r->ds, r->es, r->ss, r->fs, r->gs);
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void alarm_handler(int sig)
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fprintf(stderr, "alarm signal=%d\n", sig);
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int main(int argc, char **argv)
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struct vm86plus_struct ctx;
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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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act.sa_handler = alarm_handler;
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sigemptyset(&act.sa_mask);
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sigaction(SIGALRM, &act, NULL);
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/* load the MSDOS .com executable */
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fd = open(filename, O_RDONLY);
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ret = read(fd, vm86_mem + COM_BASE_ADDR, 65536 - 256);
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memset(&ctx, 0, sizeof(ctx));
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/* init basic registers */
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seg = (COM_BASE_ADDR - 0x100) >> 4;
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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 $0x21 */
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*seg_to_linear(r->cs, 3) = 0x21;
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pushw(&ctx.regs, 0x0000);
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/* the value of these registers seem to be assumed by pi_10.com */
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ret = vm86(VM86_ENTER, &ctx);
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switch(VM86_TYPE(ret)) {
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int_num = VM86_ARG(ret);
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ah = (r->eax >> 8) & 0xff;
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case 0x00: /* exit */
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case 0x02: /* write char */
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case 0x09: /* write string */
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c = *seg_to_linear(r->ds, r->edx);
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r->eax = (r->eax & ~0xff) | '$';
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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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/* a signal came, we just ignore that */
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fprintf(stderr, "unhandled vm86 return code (0x%x)\n", ret);
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dump_regs(&ctx.regs);