NEWS: document changes in 4.07

[profile/ivi/syslinux.git] / mbr / mbr.S

diff --git a/mbr/mbr.S b/mbr/mbr.S
index ac24b74..b71cfb7 100644 (file)
--- a/mbr/mbr.S
+++ b/mbr/mbr.S
@@ -1,6 +1,7 @@
 /* -----------------------------------------------------------------------
  *
- *   Copyright 2007 H. Peter Anvin - All Rights Reserved
+ *   Copyright 2007-2009 H. Peter Anvin - All Rights Reserved
+ *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
  *
  *   Permission is hereby granted, free of charge, to any person
  *   obtaining a copy of this software and associated documentation
@@ -25,6 +26,8 @@
  *
  * ----------------------------------------------------------------------- */
 
+#include "adjust.h"
+
        .code16
        .text
 
@@ -34,7 +37,8 @@ driveno               = (stack-6)
 sectors                = (stack-8)
 secpercyl      = (stack-12)
 
-BIOS_page = 0x462
+BIOS_kbdflags  = 0x417
+BIOS_page      = 0x462
 
        /* gas/ld has issues with doing this as absolute addresses... */
        .section ".bootsec", "a", @nobits
@@ -45,15 +49,14 @@ bootsec:
        .text
        .globl  _start
 _start:
+       .byte   0x33, 0xc0      /* xorw %ax, %ax */
        cli
-       xorw    %ax, %ax
        movw    %ax, %ds
        movw    %ax, %ss
        movw    $stack, %sp
        movw    %sp, %si
        pushw   %es             /* es:di -> $PnP header */
        pushw   %di
-       pushw   %dx             /* dl -> drive number */
        movw    %ax, %es
        sti
        cld
@@ -64,11 +67,14 @@ _start:
        rep; movsw
 
        ljmpw   $0, $next
-
 next:
+
+       ADJUST_DRIVE
+       pushw   %dx             /* dl -> drive number */
+
        /* Check to see if we have EBIOS */
        pushw   %dx             /* drive number */
-       movw    $0x4100, %ax
+       movb    $0x41, %ah      /* %al == 0 already */
        movw    $0x55aa, %bx
        xorw    %cx, %cx
        xorb    %dh, %dh
@@ -93,19 +99,22 @@ next:
        int     $0x13
        andw    $0x3f, %cx      /* Sector count */
        pushw   %cx             /* Save sectors on the stack */
-       xorw    %ax, %ax
-       pushw   %ax             /* High word of sectors/cylinder */
-       movb    %dh, %al        /* dh = number of heads */
-       incw    %ax             /* From 0-based to count */
+       movzbw  %dh, %ax        /* dh = max head */
+       incw    %ax             /* From 0-based max to count */
        mulw    %cx             /* Heads*sectors -> sectors per cylinder */
-       pushw   %ax             /* Save sectors/cylinder on the stack */
+
+       /* Save sectors/cylinder on the stack */
+       pushw   %dx             /* High word */
+       pushw   %ax             /* Low word */
 
        xorl    %eax, %eax      /* Base */
        cdq                     /* Root (%edx <- 0) */
        call    scan_partition_table
 
        /* If we get here, we have no OS */
-       jmp     missing_os
+missing_os:
+       call    error
+       .ascii  "Missing operating system.\r\n"
 
 /*
  * read_sector: read a single sector pointed to by %eax to 0x7c00.
@@ -125,6 +134,7 @@ read_sector:
 
        /* This chunk is skipped if we have ebios */
        /* Do not clobber %eax before this chunk! */
+       /* This also relies on %bx and %edx as set up above. */
 read_sector_cbios:
        divl    (secpercyl)
        shlb    $6, %ah
@@ -140,7 +150,7 @@ read_sector_cbios:
 read_common:
        movb    (driveno), %dl
        int     $0x13
-       addw    $16, %sp        /* Drop DAPA */
+       leaw    16(%si), %sp    /* Drop DAPA */
        popal
        ret
 
@@ -202,8 +212,8 @@ scan_partition_table:
        jns     too_many_active
 
        /* No active partitions found, look for extended partitions */
-       popw    %bx             /* %bx <- ptab */
        popw    %cx             /* %cx <- 4    */
+       popw    %bx             /* %bx <- ptab */
 7:
        movb    4(%bx), %al
        cmpb    $0x0f, %al      /* 0x0f = Win9x extended */
@@ -241,6 +251,10 @@ scan_partition_table:
        popal
        ret
 
+too_many_active:
+       call    error
+       .ascii  "Multiple active partitions.\r\n"
+
 /*
  * boot: invoke the actual bootstrap. (%si) points to the partition
  *      table entry, and 28(%bp) has the partition table base.
@@ -253,46 +267,33 @@ boot:
        jc      disk_error
        cmpw    $0xaa55, (bootsec+510)
        jne     missing_os              /* Not a valid boot sector */
-       movw    $driveno, %sp
+       movw    $driveno, %sp   /* driveno == bootsec-6 */
        popw    %dx             /* dl -> drive number */
        popw    %di             /* es:di -> $PnP vector */
        popw    %es
        cli
-       jmp     bootsec
+       jmpw    *%sp            /* %sp == bootsec */
 
-/*
- * error messages
- */
-missing_os:
-       movw    $missing_os_msg, %si
-       jmp     error
 disk_error:
-       movw    $disk_error_msg, %si
-       jmp     error
-too_many_active:
-       movw    $too_many_active_msg, %si
-       /* jmp error */
+       call    error
+       .ascii  "Operating system load error.\r\n"
 
+/*
+ * Print error messages.  This is invoked with "call", with the
+ * error message at the return address.
+ */
 error:
+       popw    %si
 2:
        lodsb
-       andb    %al, %al
-       jz      3f
        movb    $0x0e, %ah
        movb    (BIOS_page), %bh
        movb    $0x07, %bl
-       int     $0x10
-       jmp     2b
-3:
+       int     $0x10           /* May destroy %bp */
+       cmpb    $10, %al        /* Newline? */
+       jne     2b
+
        int     $0x18           /* Boot failure */
-       jmp     .               /* Die */
-
-missing_os_msg:
-       .ascii  "Missing operating system."
-       .byte   0
-disk_error_msg:
-       .ascii  "Operating system load error."
-       .byte   0
-too_many_active_msg:
-       .ascii  "Multiple active partitions."
-       .byte   0
+die:
+       hlt
+       jmp     die