Proposal: multiboot-kluge 'load_end' and 'load_bss' fields

[Yuri Zaporogets]

Hello guys!

It's quite a generic story - I'm writing a microkernel and use a nice
feature of GRUB called "Multiboot kluge". I use RDOFF2, a NASM
home-grown binary format. In its current version (0.98.31) RDOFF linker
'ldrdf' supports multiboot header "right out of the box" using a special
technique, namely "hardcode the trampoline code into the linker" :)

It's actually a quick-and-dirty hack which I would like to get rid of.
Instead, multiboot header and trampoline code will be in a separate file,
that can be embedded into the kernel header at linking stage.

The problem is that trampoline doesn't know the size of target kernel
image in advance; therefore, it's impossible to initialize 'load_end'
and 'bss_end' fields in the MB header to the correct values.

It would be great if I could specify something like '-1' for these
values. It might be a hint for the boot loader to load *entire* kernel
file and assume there is no BSS. I.e.

  if (load_end_addr == -1)
        load_end_addr = load_addr + filemax;
  if (bss_end_addr == -1)
        bss_end_addr = load_end_addr;
        
I think it's not hard to implement such a feature - only a few lines
in 'boot.c' and 'mbchk.c' need to be changed. If you consider it might
be useful for the future 0.7 Multiboot specification - I would be glad
to send a patch against grub-0.92.

Thanks.

P.S. (in case you're wondering why I need this. RDOFF is Relocatable
Dynamic format; it means that kernel needs to be relocated to its 
working area before start. Moreover, kernel lives in low memory; 
that's why a special setup code is needed. It's a plain binary, linked
absolutely with org=100000h and it's just glued to the kernel image.
To move this setup to 100000h a special 24-byte trampoline is used, 
which is embedded into the kernel together with a multiboot header.. %-)

73!

-- 
Regards,
Yuri Zaporogets.

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