[gPXE-devel] [PATCH v3][lkrn] add ramdisk support

[Michael Brown]

On Thursday 03 Jun 2010 08:32:55 Wu Fengguang wrote:
> > You are right.  We need a clean way to pass the off-limits region to
> > relocate().
> >
> > Generic code can't access lkrnprefix.S symbols but it should be
> > possible to pass an (addr, size) pair or even a pointer to an array of
> > (addr, size) pairs.
> 
> Yes! This is actually what I've been thinking: a little less
> straightforward, however a more modular approach.

Do you see anything wrong with Shao Miller's approach:

  http://git.etherboot.org/?p=people/sha0/gpxe.git;a=commitdiff;h=e9516971

It's pretty straightforward, and solves the problem.  The only reason I 
haven't yet merged it in to iPXE is because I'm wondering if there's a way to 
(neatly) pass max_addr in via a register, as is done with all other parameters 
in the prefix code.

(The problem of using memory for parameter passing is that the ROM prefix 
sometimes executes with a read-only .prefix.  Consequently all of the generic 
prefix code is written to assume that .prefix is non-writeable.  While it's true 
that the ROM prefix wouldn't need to override max_addr, I'd prefer to avoid 
introducing that kind of inconsistency.  We could pass parameters via the 
stack but, again, that would introduce an inconsistency since currently 
everything is passed in registers.)

Michael