exec proper wine based on arch of PE binary

wine-arch-detector.c

/* Register with:
 * echo :wine:M::MZ::/opt/wine-arch-detector:PO > /proc/sys/fs/binfmt_misc/register
 */
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <sys/auxv.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int main(int argc, char ** argv)
{
  struct stat st;
  FILE * fh;
  unsigned long atexecfd;
  int lfa;
  unsigned short machine;
  unsigned char ub[4];

  if (argc < 3)
  {
    fprintf(stderr, "Usage: %s <file> <argv0> ...\n", argv[0]);
    return 1;
  }
  atexecfd = getauxval(AT_EXECFD);
  if (atexecfd)
    fh = fdopen(atexecfd, "rb");
  else
    fh = fopen(argv[1], "rb");
  if (!fh)
  {
    fprintf(stderr, "%s: %s\n", argv[1], strerror(errno));
    return 2;
  }
  if (fstat(fileno(fh), &st) != 0)
  {
    fprintf(stderr, "%s: %s\n", argv[1], strerror(errno));
    fclose(fh);
    return 2;
  }
  if (st.st_size < 256)
  {
    fprintf(stderr, "%s: File too small\n", argv[1]);
    fclose(fh);
    return 2;
  }
  if (fread(ub, 2, 1, fh) != 1)
  {
    fprintf(stderr, "%s: Short read\n", argv[1]);
    fclose(fh);
    return 2;
  }
  if (ub[0] != 'M' || ub[1] != 'Z')
  {
    fprintf(stderr, "%s: File does not start with MZ\n", argv[1]);
    fclose(fh);
    return 2;
  }
  if (fseek(fh, 60, SEEK_SET) != 0)
  {
    fprintf(stderr, "%s: %s\n", argv[1], strerror(errno));
    fclose(fh);
    return 2;
  }
  if (fread(ub, 4, 1, fh) != 1)
  {
    fprintf(stderr, "%s: Short read\n", argv[1]);
    fclose(fh);
    return 2;
  }

  lfa = (int)((unsigned int)ub[3] << 24 | (unsigned int)ub[2] << 16 | (unsigned int)ub[1] << 8 | ub[0]);
  if (lfa <= 0 || lfa >= st.st_size)
  {
    fprintf(stderr, "%s: PE header offset out of bounds\n", argv[1]);
    fclose(fh);
    return 2;
  }
  if (fseek(fh, lfa, SEEK_SET) != 0)
  {
    fprintf(stderr, "%s: %s\n", argv[1], strerror(errno));
    fclose(fh);
    return 2;
  }

  if (fread(ub, 4, 1, fh) != 1)
  {
    fprintf(stderr, "%s: Short read\n", argv[1]);
    fclose(fh);
    return 2;
  }
  if (ub[0] != 'P' || ub[1] != 'E' || ub[2] != 0 || ub[3] != 0)
  {
    fprintf(stderr, "%s: PE header not found\n", argv[1]);
    fclose(fh);
    return 2;
  }
  if (fread(ub, 2, 1, fh) != 1)
  {
    fprintf(stderr, "%s: Short read\n", argv[1]);
    fclose(fh);
    return 2;
  }
  machine = (unsigned short)ub[1] << 8 | ub[0];
#ifdef _DEBUG
  printf("%s: machine 0x%04hx\n", argv[1], machine);
#endif
  fclose(fh);
  /* TODO: should I register without P flag and replace argv[0] instead? */
  argv[2] = argv[1];
  switch (machine)
  {
  case 0x014c:
  case 0x8664:
    argv[1] = "/usr/bin/wine";
    break;
  case 0xaa64:
    argv[1] = "/usr/bin/wine-arm64";
    break;
  default:
    fprintf(stderr, "%s: Unhandled machine type in PE file %s: 0x%04hx\n", argv[0], argv[1], machine);
    return 3;
  }
  execv(argv[1], &argv[1]);
  fprintf(stderr, "%s: Error execing %s: %s\n", argv[0], argv[1], strerror(errno));

  return 5;
}