gptmbr: save phdr -> bootsect on the stack, saving one byte

diff --git a/mbr/gptmbr.S b/mbr/gptmbr.S
index 10dfd45..4009643 100644 (file)
--- a/mbr/gptmbr.S
+++ b/mbr/gptmbr.S
@@ -115,6 +115,7 @@ next:
        xorl    %edx,%edx
        incw    %ax
        movw    $phdr, %bx
+       pushw   %bx             /* -8(%bp) phdr == bootsect */
        call    read_sector
 
        /* Number of partition sectors */
@@ -189,12 +190,13 @@ found_part:
 
 /*
  * boot: invoke the actual bootstrap. %ds:%si points to the
- * partition information in memory.
+ * partition information in memory.  The top word on the stack
+ * is phdr == 0x7c00 == the address of the boot sector.
  */
 boot:
        movl    (32+16)(%si),%eax
        movl    (36+16)(%si),%edx
-       movw    $bootsec,%bx
+       popw    %bx
        call    read_sector
        cmpw    $0xaa55, -2(%bx)
        jne     missing_os      /* Not a valid boot sector */