[src/trunk]: src/sys/arch/i386/stand/lib Don't trust %bp to point to same pla...

[dsl <dsl%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/e0d5c563e6fd
branches:  trunk
changeset: 544019:e0d5c563e6fd
user:      dsl <dsl%NetBSD.org@localhost>
date:      Sat Mar 08 21:09:37 2003 +0000

description:
Don't trust %bp to point to same place in real and protected modes.
prot_to_real preserves %ebp but changes %ss and %sp.
(ok if real %ss is offset n*64k from protected %ss - which it has been)

diffstat:

 sys/arch/i386/stand/lib/bios_disk.S |  23 +++++++++++------------
 1 files changed, 11 insertions(+), 12 deletions(-)

diffs (49 lines):

diff -r e129c2145053 -r e0d5c563e6fd sys/arch/i386/stand/lib/bios_disk.S
--- a/sys/arch/i386/stand/lib/bios_disk.S       Sat Mar 08 20:50:58 2003 +0000
+++ b/sys/arch/i386/stand/lib/bios_disk.S       Sat Mar 08 21:09:37 2003 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: bios_disk.S,v 1.11 2003/02/05 21:41:51 dsl Exp $       */
+/*     $NetBSD: bios_disk.S,v 1.12 2003/03/08 21:09:37 dsl Exp $       */
 
 /*
  * Ported to boot 386BSD by Julian Elischer (julian%tfs.com@localhost) Sept 1992
@@ -125,29 +125,28 @@
        orb     %al, %cl
        incb    %cl             # sector; sec starts from 1, not 0
        movb    8(%ebp), %dl    # device
+       movl    28(%ebp), %ebx  # buffer address (may be >64k)
+       movb    24(%ebp), %al   # number of sectors
 
        call    _C_LABEL(prot_to_real)  # enter real mode
        .code16
 
-       movl    28(%bp), %ebx   # buffer address (may be >64k)
-       movl    %ebx, %eax
-       shrl    $4, %eax        # max segment
-       andl    $0xf, %ebx      # and min offset - to avoid overrun
+       push    %bx
+       shrl    $4, %ebx        # max segment
        mov     %ds, %si
-       add     %si, %ax
-       mov     %ax, %es        # %es:%bx now valid buffer address
+       add     %si, %bx
+       mov     %bx, %es        # %es:%bx now valid buffer address
+       pop     %bx
+       and     $0xf, %bx       # and min offset - to avoid overrun
 
        movb    $0x2, %ah       # subfunction
-       movb    24(%bp), %al    # number of sectors
        int     $0x13
-       setc    %bl
-       movb    %ah, %bh        # save error code
+       setc    %al             # error code is in %ah
        
        calll   _C_LABEL(real_to_prot) # back to protected mode
        .code32
 
-       xorl    %eax, %eax
-       movw    %bx, %ax        # return value in %ax
+       andl    $0xffff, %eax
 
        pop     %edi
        pop     %esi