2005-02-15 Yoshinori K. Okuji <okuji@enbug.org>

* stage2/builtins.c (install_func): If DEST_DRIVE is a hard
  disk, enable the workaround in Stage 1 by replacing the jmp
  with double nop's.

  * stage1/stage1.h (STAGE1_BOOT_DRIVE_CHECK): New macro.
  (STAGE1_BOOT_DRIVE_MASK): Removed.

  * stage1/stage1.S (boot_drive_check): New label. This implements
  a different workaround for buggy BIOSes which don't pass boot
  drive correctly. This is effective for BIOSes which pass a value
  without the seventh bit (0x80).
  (boot_drive_mask): Removed.

stage1/stage1.S

@@ -108,12 +108,18 @@ after_BPB:
 
 	/*
 	 * This is a workaround for buggy BIOSes which don't pass boot
-	 * drive correctly. If GRUB is installed into a HDD, do
-	 * "orb $0x80, %dl", otherwise "orb $0x00, %dl" (i.e. nop).
+	 * drive correctly. If GRUB is installed into a HDD, check if
+	 * DL is masked correctly. If not, assume that the BIOS passed
+	 * a bogus value and set DL to 0x80, since this is the only
+	 * possible boot drive. If GRUB is installed into a floppy,
+	 * this does nothing (only jump).
 	 */
-	.byte	0x80, 0xca
-boot_drive_mask:
-	.byte	0x00
+boot_drive_check:	
+	jmp	1f
+	testb	$0x80, %dl
+	jnz	1f
+	movb	$0x80, %dl
+1:	
 
 	/*
 	 * ljmp to the next instruction because some bogus BIOSes

stage1/stage1.h

@@ -51,8 +51,8 @@
 /* The offset of STAGE2_SEGMENT.  */
 #define STAGE1_STAGE2_SEGMENT	0x48
 
-/* The offset of BOOT_DRIVE_MASK.  */
-#define STAGE1_BOOT_DRIVE_MASK	0x4d
+/* The offset of BOOT_DRIVE_CHECK.  */
+#define STAGE1_BOOT_DRIVE_CHECK	0x4b
 
 /* The offset of a magic number used by Windows NT.  */
 #define STAGE1_WINDOWS_NT_MAGIC	0x1b8