Re: [SeaBIOS] [PATCH RFC 1/7] Only use -fomit-frame-pointer with 32bit flat code

[Kevin O'Connor]

On Fri, Dec 16, 2011 at 02:15:07PM +0000, Julian Pidancet wrote:
> The real-mode emulator that Windows 7 uses to execute the vga bios rom
> becomes very confused when the code tries to dereference the stack
> pointer instead of using the frame pointer, leading to corruption of
> parameters passed on the stack from one function to another.
>
> Signed-off-by: Julian Pidancet

Wow - I can only imagine how hard it was to find that.

I'm okay with turning off omit-frame-pointer for the vga bios.
However, I'd prefer not to turn it off for the main seabios build.
Does the emulator also try to emulate parts of the BIOS, which would
make that a problem?

-Kevin

[PATCH RFC 1/7] Only use -fomit-frame-pointer with 32bit flat code

[Julian Pidancet]

On Sat, Dec 17, 2011 at 3:38 PM, Kevin O'Connor  wrote:
> On Fri, Dec 16, 2011 at 02:15:07PM +0000, Julian Pidancet wrote:
> > The real-mode emulator that Windows 7 uses to execute the vga bios rom
> > becomes very confused when the code tries to dereference the stack
> > pointer instead of using the frame pointer, leading to corruption of
> > parameters passed on the stack from one function to another.
> >
> > Signed-off-by: Julian Pidancet
>
> Wow - I can only imagine how hard it was to find that.
>
> I'm okay with turning off omit-frame-pointer for the vga bios.
> However, I'd prefer not to turn it off for the main seabios build.
> Does the emulator also try to emulate parts of the BIOS, which would
> make that a problem?

Besides the functions which are common to both the BIOS and the VGA
ROM ( src/output.c and src/util.c), it doesn't seem to make any
particular problem with the rest of the BIOS.

Julian.