MBR: always do setup for EBIOS, makes stack handling easier and saves jmp

diff --git a/mbr/mbr.S b/mbr/mbr.S
index 43b2983..9e89b37 100644 (file)
--- a/mbr/mbr.S
+++ b/mbr/mbr.S
@@ -80,8 +80,8 @@ next:
        shrw    %cx             /* Bit 0 = fixed disk subset */
        jnc     1f
 
-       /* We have EBIOS; patch in a jump to read_sector_ebios */
-       movw    $0xeb+((read_sector_ebios-read_sector_cbios-2)<< 8), (read_sector_cbios)
+       /* We have EBIOS; patch in jump to skip over read_sector_cbios */
+       movw    $0xeb+((read_common-read_sector_cbios-2)<< 8), (read_sector_cbios)
 
 1:
        popw    %dx
@@ -111,9 +111,18 @@ next:
  */
 read_sector:
        pushal
-       movw    %sp, %bp
        xorl    %edx, %edx
        movw    $bootsec, %bx
+       pushl   %edx    /* MSW of LBA */
+       pushl   %eax    /* LSW of LBA */
+       pushw   %es     /* Buffer segment */
+       pushw   %bx     /* Buffer offset */
+       pushw   $1      /* Sector count */
+       pushw   $16     /* Size of packet */
+       movw    %sp, %si
+       movb    $0x42, %ah
+
+       /* This chunk is skipped if we have ebios */
 read_sector_cbios:
        divl    (secpercyl)
        shlb    $6, %ah
@@ -125,20 +134,11 @@ read_sector_cbios:
        orb     %ah, %cl
        incw    %cx     /* Sectors are 1-based */
        movw    $0x0201, %ax
-       jmp     read_common
-read_sector_ebios:
-       pushl   %edx    /* MSW of LBA */
-       pushl   %eax    /* LSW of LBA */
-       pushw   %es     /* Buffer segment */
-       pushw   %bx     /* Buffer offset */
-       pushw   $1      /* Sector count */
-       pushw   $16     /* Size of packet */
-       movw    %sp, %si
-       movb    $0x42, %ah
+
 read_common:
        movb    (driveno), %dl
        int     $0x13
-       movw    %bp, %sp
+       addw    $16, %sp        /* Drop DAPA */
        popal
        ret