[ros-dev] multiboot.S patch in need of review, please
tamlin at algonet.se
Thu Jan 27 05:23:21 CET 2005
Jonathan Wilson wrote:
> > I think freeldr shoudl be modified to PE load the boot drivers and
> > ntoskrnl, instead of just memory dumping. This should remove most of the
> > bss hacks which use kernel_base, and the rest should use whatever
> > freeldr pushes on the loader_block. For now, we were simply testing some
> > things, and Royce's patch still helps a lot.
> How does windows do this?
> I gather it does this through NTLDR but what does NTLDR do here?
While I haven't really verified this, so I can't be 100% sure, I strongly
suspect it does the Right Thing(tm) - PE loads the modules.
This discussion has been going round and round since basically the time I
got kernel+hal to compile with MSVC. I had to do some seriously cludgy
1) "inject" the multiboot header (which is basically just a few bytes
telling multiboot "load this image at this hardware address, clean the
memory between x and y for BSS use, and then jump to this absolute address
afterwards - much like the C64 loaded and ran binary images), and
2) in-place relocate ntoskrnl.exe (this is before paging is turned on, why
it was a little tricky to do from a combination of C and inline assembler
:-) ). The MinGW build don't have this "problem", since it uses page-sized
section alignment (meaning its layout is quite different from a kernel image
from an NT system), and depended on GCC-internal stuff to get BSS segment
and so on.
The solution is quite obvious: Create a small loader that is multiboot-able
(and get loaded by the multiboot-loader loading boot program), that in turn
loads the kernel(+hal IIRC) and relocates, makes sure BSS is zero, and jumps
to the PE-designated entry-point.
More information about the Ros-dev