MBR: Don't clobber %eax before entering CBIOS code

diff --git a/mbr/mbr.S b/mbr/mbr.S
index 9e89b37..b9729eb 100644 (file)
--- a/mbr/mbr.S
+++ b/mbr/mbr.S
@@ -80,8 +80,10 @@ next:
        shrw    %cx             /* Bit 0 = fixed disk subset */
        jnc     1f
 
-       /* We have EBIOS; patch in jump to skip over read_sector_cbios */
-       movw    $0xeb+((read_common-read_sector_cbios-2)<< 8), (read_sector_cbios)
+       /* We have EBIOS; patch in the following code at
+          read_sector_cbios: movb $0x42, %ah ;  jmp read_common */
+       movl    $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \
+               (read_sector_cbios)
 
 1:
        popw    %dx
@@ -120,9 +122,9 @@ read_sector:
        pushw   $1      /* Sector count */
        pushw   $16     /* Size of packet */
        movw    %sp, %si
-       movb    $0x42, %ah
 
        /* This chunk is skipped if we have ebios */
+       /* Do not clobber %eax before this chunk! */
 read_sector_cbios:
        divl    (secpercyl)
        shlb    $6, %ah