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Don't trust %bp to point to same place in real and protected modes.

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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)
This commit is contained in:
dsl 2003-03-08 21:09:37 +00:00
parent d4bb6dd255
commit ef18027d4d
1 changed files with 11 additions and 12 deletions
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23
sys/arch/i386/stand/lib/bios_disk.S
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@ -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) Sept 1992
@ -125,29 +125,28 @@ ENTRY(biosread)
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