qemu crashes on unaligned extended disk reads

[Andrew McGowen]

When performing a BIOS extended disk read (INT 13H, AH=0x42), if the offset of the buffer destination in the DAP (disk address packet) is not dword-aligned (i.e. a multiple of 4), SeaBIOS attempts to execute code at non-mapped address 0xb4f53, causing QEMU to crash. I imagine it's a bug in the BIOS code, but it does cause QEMU to crash.

QEMU version: 1.4.0 (Debian 1.4.0+dfsg-1expubuntu4) (from Ubuntu repository)
SeaBIOS version: 1.7.2-20130119_170942-roseapple
command line: qemu-system-x86_64 -m 64 -hda hda.img -monitor stdio
CPU: Intel Core i7 CPU M620 on a Dell Latitude E6410
OS: Ubuntu, GNU/Linux 3.8.0-25-generic, 64-bit

[Stefan Hajnoczi (stefanha)]

On Tue, Jun 18, 2013 at 09:23:31PM -0000, Andrew McGowen wrote:
> When performing a BIOS extended disk read (INT 13H, AH=0x42), if the
> offset of the buffer destination in the DAP (disk address packet) is not
> dword-aligned (i.e. a multiple of 4), SeaBIOS attempts to execute code
> at non-mapped address 0xb4f53, causing QEMU to crash. I imagine it's a
> bug in the BIOS code, but it does cause QEMU to crash.

Can you post details on the "crash"? What is the error message?

Stefan

[Andrew McGowen (akmcgowen)]

...well this is embarrassing - it was an issue with my code not saving/restoring registers on the stack properly.

[Thomas Huth (th-huth)]

Marking this ticket as "Invalid" according to comment #2.