Here is a patch which I believe should detect a modern MBR format
and refuse to overwrite it, and hence avoid breaking windows vista+,
although of course with an option to use --force to do it anyhow.
I did not test it yet since I don't have a system handy that I could
test it on.
Fixing install-mbr to actually support modern MBR format would change
the format and make it incompatible with older versions and is a lot
more work, but at least preventing the breaking of the existing OSs is
pretty simple.
--
Len Sorensen
--- mbr-1.1.11.orig/install-mbr.c 2015-03-05 10:47:13.000000000 -0500
+++ mbr-1.1.11/install-mbr.c 2015-03-05 10:45:54.639111226 -0500
@@ -829,6 +829,26 @@
exit(1);
}
+ /* Check for modern MBR format (which install-mbr does NOT currently support)
+ If bytes 445 and 446 are either 0x0000 or 0x5A5A and bytes 440-443
+ are non zero, then it is very likely to be a modern MBR and we should
+ NOT overwrite it since that would break Windows Vista and higher. */
+ if ((dp->flags & DFLAG_FORCE) == 0 &&
+ (mbr_in[CODE_SIZE-6] != 0x00 ||
+ mbr_in[CODE_SIZE-5] != 0x00 ||
+ mbr_in[CODE_SIZE-4] != 0x00 ||
+ mbr_in[CODE_SIZE-3] != 0x00) &&
+ ((mbr_in[CODE_SIZE-2] == 0x00 && mbr_in[CODE_SIZE-1] == 0x00) ||
+ (mbr_in[CODE_SIZE-2] == 0x5A && mbr_in[CODE_SIZE-1] == 0x5A)))
+ {
+ fprintf(stderr, "%s:%s: Probable detection of modern MBR format which is "
+ "currently incompatible with install-mbr. Installing will probably "
+ "break Windows installations on this system. "
+ "Use --force to override.\n", prog_name,
+ dp->target.path);
+ exit(1);
+ }
+
/* Try to extract the parameters unless we're resetting them. If we
are resetting, or the extraction fails, reset them anyway. */
if ((dp->flags & DFLAG_RESET) != 0 ||
