altmbr: fix accounting of logical partitions

Unlike the main MBR, we need to keep careful count when we process
logical partitions... and we weren't.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/mbr/altmbr.S b/mbr/altmbr.S
index 4a502ed..794ab62 100644 (file)
--- a/mbr/altmbr.S
+++ b/mbr/altmbr.S
@@ -195,31 +195,30 @@ scan_partition_table:
        /* Scan the primary partition table */
        movw    $ptab, %si
        movw    $4, %cx
+       /* Is it a primary partition table? */
+       andl    %edx, %edx
+       jnz     7f
        push    %si
        push    %cx
 
-       /* Is it a primary partition? */
-       andl    %edx, %edx
-       jnz     6f
-
 5:
        decb    (partition)
        jz      boot
        addw    $16, %bx
        loopw   5b
 
-6:
-       /* No active partitions found, look for extended partitions */
-       popw    %cx             /* %cx <- 4    */
-       popw    %si             /* %si <- ptab */
-7:
-       movl    20(%bp), %edx           /* "Root" */
+       popw    %cx                     /* %cx <- 4    */
+       popw    %si                     /* %si <- ptab */
 
+       /* No primary partitions found, look for extended/logical partitions */
+7:
        movb    4(%si), %al
-       cmpb    $0x0f, %al      /* 0x0f = Win9x extended */
+       andb    %al, %al
+       jz      12f                     /* Not a valid partition */
+       cmpb    $0x0f, %al              /* 0x0f = Win9x extended */
        je      8f
-       andb    $~0x80, %al     /* 0x85 = Linux extended */
-       cmpb    $0x05, %al      /* 0x05 = MS-DOS extended */
+       andb    $~0x80, %al             /* 0x85 = Linux extended */
+       cmpb    $0x05, %al              /* 0x05 = MS-DOS extended */
        jne     9f
 
        /* It is an extended partition.  Read the extended partition and
@@ -243,9 +242,8 @@ scan_partition_table:
        /* fall through */
 9:
        /* Not an extended partition */
-       andb    %al, %al
-       jz      12f                     /* Not a valid partition */
        andl    %edx, %edx              /* Are we inside an extended part? */
+       jz      12f
        /* If so, this is a logical partition */
        decb    (partition)
        je      boot