isohdpfx: actually generate the stack frame isolinux expects

Actually generate the stack frame isolinux expects.  This is not the
optimal order, but it appears to be what both earlier and later
versions of isolinux expects...

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S
index 375c846..801115c 100644 (file)
--- a/mbr/isohdpfx.S
+++ b/mbr/isohdpfx.S
@@ -48,9 +48,9 @@ isolinux_start_hybrid         = 0x7c00+64+4
 stack          = 0x7c00
 partoffset     = (stack-8)
 driveno                = (stack-14)
-ebios_flag     = (stack-16)
+heads          = (stack-16)
 sectors                = (stack-18)
-heads          = (stack-20)
+ebios_flag     = (stack-20)
 secpercyl      = (stack-24)
 
 BIOS_kbdflags  = 0x417
@@ -138,18 +138,21 @@ next:
        jmp     1f
 1:
        popw    %dx
-       pushw   %cx             /* -16: Save EBIOS flag */
+       pushw   %cx             /* EBIOS flag */
 
        /* Get (C)HS geometry */
        movb    $0x08, %ah
        int     $0x13
        andw    $0x3f, %cx      /* Sector count */
-       pushw   %cx             /* -18: Save sectors on the stack */
+       popw    %bx             /* EBIOS flag */
+       pushw   %cx             /* -16: Save sectors on the stack */
        movzbw  %dh, %ax        /* dh = max head */
        incw    %ax             /* From 0-based max to count */
-       pushw   %ax             /* -20: Save heads on the stack */
+       pushw   %ax             /* -18: Save heads on the stack */
        mulw    %cx             /* Heads*sectors -> sectors per cylinder */
 
+       pushw   %bx             /* -20: EBIOS flag */
+       
        /* Save sectors/cylinder on the stack */
        pushw   %dx             /* -22: High word */
        pushw   %ax             /* -24: Low word */
@@ -177,7 +180,7 @@ next:
        jne     bad_signature
 
        cli
-       movw    $heads, %sp
+       movw    $ebios_flag, %sp
 
        /*
         * Use a ljmpw here to work around a bug in some unknown version