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

[Paolo Bonzini]

On 12/16/2011 03:15 PM, 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
>
> Makefile |    4 ++--
>   1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index c3ba2f3..cb00958 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -32,14 +32,14 @@ COMMONCFLAGS = -I$(OUT) -Os -MD \
>                  $(call cc-option,$(CC),-Wtype-limits,) \
>                  -m32 -march=i386 -mregparm=3 -mpreferred-stack-boundary=2 \
>                  -mrtd -minline-all-stringops \
>           -freg-struct-return -ffreestanding -fomit-frame-pointer \
>           -freg-struct-return -ffreestanding \
>            -fno-delete-null-pointer-checks \
>            -ffunction-sections -fdata-sections -fno-common
> COMMONCFLAGS += $(call cc-option,$(CC),-nopie,)
> COMMONCFLAGS += $(call cc-option,$(CC),-fno-stack-protector,)
> COMMONCFLAGS += $(call cc-option,$(CC),-fno-stack-protector-all,)
>
> -CFLAGS32FLAT = $(COMMONCFLAGS) -g -DMODE16=0 -DMODESEGMENT=0
> +CFLAGS32FLAT = $(COMMONCFLAGS) -fomit-frame-pointer -g -DMODE16=0 -DMODESEGMENT=0
>   CFLAGSSEG = $(COMMONCFLAGS) -DMODESEGMENT=1 -fno-defer-pop \
>               $(call cc-option,$(CC),-fno-jump-tables,-DMANUAL_NO_JUMP_TABLE) \
>               $(call cc-option,$(CC),-fno-tree-switch-conversion,)

Ouch.  I can imagine how fun it must have been to debug this.  Good catch.

Paolo