Syslinux - Aug 2006 - Fair warning regarding the future of the COM32 format

Hi all,

I just want to give everyone a heads-up that I'm considering removing 
support for COM32 in favour of relocatable (-fPIC) ELF files, or some 
other relocatable format.  This would allow one "ELFCOM" file to call 
out to another, and then return.

Part of the idea here is to run the main syslinux UI and probably the 
filesystem drivers in "ELFCOM" code, which doesn't work too well
with
everything being statically linked to a fixed address.

The other option, which I am also considering, is to do the same thing 
by playing games with segments.  This would break COM32 files which rely 
on touching fixed addresses (which most of them currently do), but would 
otherwise be a relatively straightforward operation.  If I do that, I'll 
  introduce a standard GDT which would have flat segments as well as 
fixed-offset ones, but you'd still have to convert pointers before 
passing them to something.  It's not clear to me at this time which way 
is better, although I think I am leaning toward the former.

	-hpa

> I just want to give everyone a heads-up that I'm considering removing 
> support for COM32 in favour of relocatable (-fPIC) ELF files, or some 
> other relocatable format.  This would allow one "ELFCOM" file to
call
> out to another, and then return.
> 
> Part of the idea here is to run the main syslinux UI and probably the 
> filesystem drivers in "ELFCOM" code, which doesn't work too
well with
> everything being statically linked to a fixed address.
That sounds great!  What kind of support will there be for dynamically
allocating memory when multiple ELFCOM modules are loaded?  I'm thinking
of the multiboot loader, which needs to allocate potentially quite large
amounts of memory and be sure they will be safe from other modules.

Tim.

-- 
Tim Deegan                           (My opinions, not the University's)
Systems Research Group
University of Cambridge Computer Laboratory