[PATCH] Fix boot device in chainloader

[PATCH] Fix boot device in chainloader

[Pavel Roskin]

Hello!

That's a very serious bug, which prevents Windows Vista from loading
(and perhaps many other OSes depend on it too).  Applying the patch
fixes it.  The patch needs to be applied before 1.96 is released, if
possible.

The boot drive setting is held in the %edx register, which is clobbered
by grub_gate_a20() when called from grub_chainloader_real_boot().  %edx
and %esi are preserved around grub_dl_unload_all(), but not around
grub_gate_a20().

I'm not sure, but the bug may be relevant to the thread "root seems to
be incorrectly set after install".

 ChangeLog              |    6 ++++++
 kern/i386/pc/startup.S |    8 ++++----
 2 files changed, 10 insertions(+), 4 deletions(-)


diff --git a/ChangeLog b/ChangeLog
index c92168b..eb5d8ad 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2008-02-03  Pavel Roskin  <proski@gnu.org>
+
+	* a/kern/i386/pc/startup.S (grub_chainloader_real_boot): Pop
+	%edx and %esi from stack only after grub_gate_a20() is called.
+	grub_gate_a20() clobbers %edx.
+
 2008-02-03  Yoshinori K. Okuji  <okuji@enbug.org>
 
 	* configure.ac (AC_INIT): Bumped to 1.96.
diff --git a/kern/i386/pc/startup.S b/kern/i386/pc/startup.S
index e4101a6..0bfe2b3 100644
--- a/kern/i386/pc/startup.S
+++ b/kern/i386/pc/startup.S
@@ -594,16 +594,16 @@ FUNCTION(grub_chainloader_real_boot)
 
 	call	EXT_C(grub_dl_unload_all)
 
+	/* Turn off Gate A20 */
+	xorl	%eax, %eax
+	call	EXT_C(grub_gate_a20)
+
 	/* set up to pass boot drive */
 	popl	%edx
 
 	/* ESI must point to a partition table entry */
 	popl	%esi
 
-	/* Turn off Gate A20 */
-	xorl	%eax, %eax
-	call	EXT_C(grub_gate_a20)
-	
 	call	prot_to_real
 	.code16
 	ljmp	$0, $GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR


-- 
Regards,
Pavel Roskin

Re: [PATCH] Fix boot device in chainloader

[Yoshinori K. Okuji]

On Sunday 03 February 2008 18:15, Pavel Roskin wrote:
> That's a very serious bug, which prevents Windows Vista from loading
> (and perhaps many other OSes depend on it too).  Applying the patch
> fixes it.  The patch needs to be applied before 1.96 is released, if
> possible.

Sorry that it's a bit too late. But thank you for finding this bug. Please go 
ahead.

Okuji

Re: [PATCH] Fix boot device in chainloader

[Pavel Roskin]

Quoting "Yoshinori K. Okuji" <okuji@enbug.org>:

> On Sunday 03 February 2008 18:15, Pavel Roskin wrote:
>> That's a very serious bug, which prevents Windows Vista from loading
>> (and perhaps many other OSes depend on it too).  Applying the patch
>> fixes it.  The patch needs to be applied before 1.96 is released, if
>> possible.
>
> Sorry that it's a bit too late. But thank you for finding this bug. Please go
> ahead.

Committed.  Hopefully 1.97 won't take too long :)

-- 
Regards,
Pavel Roskin