[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Qemu-devel] Stack corruption problem with SeaBIOS/gPXE under QEMU

From: Naphtali Sprei
Subject: [Qemu-devel] Stack corruption problem with SeaBIOS/gPXE under QEMU
Date: Thu, 12 Nov 2009 13:20:58 +0200
User-agent: Thunderbird (X11/20090817)

I've found a problem with the usage of SeaBIOS/gPXE in Qemu.
The scenario is when failing to boot from network and falling back to booting 
from hard-disk (-boot nc).
The cause of the problem is that both SeaBIOS and gPXE (in it's installation 
phase) uses same stack area, 0x7c00.
The gPXE code corrupts the SeaBIOS stack, so when gPXE returns to SeaBIOS chaos 

Output: "qemu: fatal: Trying to execute code outside RAM or ROM at 

A simple hack/patch (attached) solves this problem, but a proper patch expected 
from the SeaBIOS guys.



Patch against current SeaBIOS git

Signed-off-by: Naphtali Sprei <address@hidden>
 src/arch/i386/prefix/pxeprefix.S |    2 +-
 src/arch/i386/prefix/romprefix.S |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/arch/i386/prefix/pxeprefix.S b/src/arch/i386/prefix/pxeprefix.S
index b541e4b..11dd45d 100644
--- a/src/arch/i386/prefix/pxeprefix.S
+++ b/src/arch/i386/prefix/pxeprefix.S
@@ -47,7 +47,7 @@ FILE_LICENCE ( GPL2_OR_LATER )
        /* Set up stack just below 0x7c00 */
        xorw    %ax, %ax
        movw    %ax, %ss
-       movl    $0x7c00, %esp
+       movl    $0x7a00, %esp
        /* Clear direction flag, for the sake of sanity */
        /* Print welcome message */
diff --git a/src/arch/i386/prefix/romprefix.S b/src/arch/i386/prefix/romprefix.S
index cb474e8..93f3f17 100644
--- a/src/arch/i386/prefix/romprefix.S
+++ b/src/arch/i386/prefix/romprefix.S
@@ -587,7 +587,7 @@ exec:       /* Set %ds = %cs */
        /* Obtain a reasonably-sized temporary stack */
        xorw    %ax, %ax
        movw    %ax, %ss
-       movw    $0x7c00, %sp
+       movw    $0x7a00, %sp
        /* Install gPXE */
        movl    image_source, %esi

reply via email to

[Prev in Thread] Current Thread [Next in Thread]