[ros-dev] Endianess

[art yerkes]

On Wed, 14 Mar 2007 05:21:34 -0400
"Tristan Miller" <trismandev at gmail.com> wrote:

> Ok, sounds good.  (I could have sworn that the idata - edata were being
> created when I would objcopy -F pei-powerpc , but thats what I get for
> coding at four in the morning I suppose.  : P).  Yeah, with the lack of any
> correct tools at all, I think that we should (at least for the time being)
> move to ELF like you said.  What code repository have you been working out
> of, the powerpc branch in svn?  I've been modifying some of the OF code to
> make it BE and cleaning it up a bit.

I think the safest is for this work to be isolated in the ppc branch for now.
Trunk has had quite enough activity on its own.  If we're going BE, we can
simplify the ofw interface generator that's in there too.

> 
> And once I create something appreciable how does one go about getting write
> access, and how would it work?  Would I work out of my own branch, or out of
> trunk?
> 
> Also, a few more quick questions.  Do you what sets the memory
> commit/reserve values?  Are heuristics in the compiler applied, or are they
> just set by a linker flag?  

AFAIK they have standard defaults (64k/1meg)

> I don't have that much experience with MSVC...
> Also, without setting callbacks, or mapping OFw into your PTEG, how are you
> able to use the OF framebuffer to display text?  Are you directly writing to
> the framebuffer or using the OF client interface?
> 

I get the framebuffer address from ofw in a similar way to linux before the
mmu takeover.  After we take over the MMU, it's just us, the CPU and anything
that lives in the physical map left.  Physical writes are done by loading
the desired value and the writing it with MSR[DR]=0.  Not too clever but it
gets the job done.  My intention was to eventually map the FB, once mm had
been sorted out.  The nice thing about using my scheme is that it'll work
even if virtually everything else is broken :-)

>  Thanks
>   ~Tristan Miller
>   (monocasa)
> 
> On 3/13/07, art yerkes <ayerkes at speakeasy.net> wrote:
> >
> > The port to this point can load ntoskrnl and hal and use the OFw
> > framebuffer
> > to display text.  Freeldr has been perverted to use openfirmware to
> > allocate
> > memory and access the disk, but uses its own implementation of fat32 to
> > load
> > files.  We allocate a new PTEG area, fill it with a mapping of freeldr and
> > the kernel area and reset SDR1 just before jumping to kernel land.  I
> > haven't
> > yet written the code that either communicates our new page arrangement in
> > the
> > existing page table format or hacks what I do store for ntoskrnl's use.
> >
> > The method used to write to the display is effective but slow.  It could
> > be
> > improved.
> >
> > ABI issues have been a significant sticking point at points, mainly due to
> > the mismatch between relocation types in the ELF we're generating to be
> > linked
> > and the ultimate result PE.  Admittedly I hadn't considered BE PE-COFF
> > because
> > I had mostly given up on reactivating COFF powerpc in binutils.  I'd like
> > to
> > know what target you're using to produce pe-powerpcbe.  My experience has
> > been
> > that the out of date portions of the coff infrastructure in binutils,
> > combined
> > with all the code for dead variants of coff-powerpc makes generating
> > sensible
> > coff-powerpc output from ld hard.
> >
> > As to your question about how I'd emulate PE-coff features in elf, for
> > dynamic
> > linking I'd follow the example of mcore in dlltool, for resources I'd
> > leave it
> > as a specially named section and for the PE header, I'd make space for it
> > at
> > link time and have the loader construct it based on the elf info.  We'd
> > only
> > be missing irreplaceable information like subsystem id and memory use
> > (stack
> > commit/reserve etc), which we could bury in a well named section with some
> > implementation specific type.  The main thing we'd have to look out for is
> > that
> > once tranformed, the resulting image won't be relocatable, so the loader
> > would
> > have to find the right aperture and use elf relocation to place
> > everything.
> > --
> > The way out is via the door. Why is it that no one will use this method? -
> > Confucius
> >
> 


-- 
The way out is via the door. Why is it that no one will use this method? - Confucius