[coreboot] SeaBIOS question and cross compilation fix.

[Stefan Reinauer]

Stefan Reinauer wrote:
> Hi, Kevin,
>
> I am experimenting with v3 and better integration of SeaBIOS and
> coreboot. For that, I am copying a SeaBIOS image to the FSEG during
> coreboot's VGA init code. In addition I added another 32bit entry point
> to SeaBIOS at 0xffc0 (Thus, living at 0xfffc0)
>
> int copy_systembios(void)
> {
>         struct mem_file archive, result;
>         int ret;
>         init_archive(&archive);
>         ret = find_file(&archive, "bios.bin", &result);
>         if (ret) {
>                 printk(BIOS_WARNING, "No legacy bios found.\n");
>                 return -1;
>         }
>         process_file(&result, (void *)0xf0000);
>         return 0;
> }
>
> void run_bios(struct device *dev, unsigned long addr)
> {
>         int i;
>         void (*init_systembios)(void) = (void *)0xfffc0;
>         copy_systembios();
>         init_systembios();
>         real_mode_switch_call_vga((dev->bus->secondary << 8) |
> dev->path.pci.devfn);
> }
>
> Now, the entry point looks like this:
> diff -ur -x .git seabios2/src/romlayout.S seabios/src/romlayout.S
> --- seabios2/src/romlayout.S    2008-11-06 15:46:44.000000000 +0100
> +++ seabios/src/romlayout.S     2008-11-01 11:38:06.000000000 +0100
> @@ -544,6 +544,18 @@
>          ORG 0xff54
>          IRQ_ENTRY_ARG 05
>
> +.code32
> +        ORG 0xffc0 // coreboot Entry Point
> +       mov $0x3f8, %dx
> +       mov $0x44, %al
> +       outb %al, %dx // print
> +       call _code32__init
> +       mov $0x3f8, %dx
> +       mov $0x45, %al
> +       outb %al, %dx
> +       ret
> +.code16gcc
Ok, thanks for your hint with the gdb debugging in qemu. This is quite nice.

(gdb) disas 0xfffc0 0xfffd4
Dump of assembler code from 0xfffc0 to 0xfffd4:
0x000fffc0:    mov    $0x3f8,%dx
0x000fffc4:    mov    $0x44,%al
0x000fffc6:    out    %al,(%dx)
0x000fffc7:    call   0x1e2617
0x000fffcc:    mov    $0x3f8,%dx
0x000fffd0:    mov    $0x45,%al
0x000fffd2:    out    %al,(%dx)
0x000fffd3:    ret   

The call is actually interpreted as a call to 0x1e2617 instead of a call
to 0xf2617. Not sure where the 0x1e instead of the 0xf comes from.

out stepan$ i386-elf-nm rom.o |grep _init
000f2617 A _code32__init
000f2617 T _init

ndisasm translates the same assembler code from above as follows:

0000FFC0  66BAF803          mov dx,0x3f8
0000FFC4  B044              mov al,0x44
0000FFC6  EE                out dx,al
0000FFC7  E84B260E00        call 0xf2617
0000FFCC  66BAF803          mov dx,0x3f8
0000FFD0  B045              mov al,0x45
0000FFD2  EE                out dx,al
0000FFD3  C3                ret

so it looks like ndisasm and I made the same mistake, while qemu
interprets the code sequence differently.

Any hints?

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