Re: [Xen-devel] Xen1.2 NetBSD port snapshot available and set_gdt patch for Xen1.2

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> yes, although the loader will have to get the setup right:  we need an ELF
> header in front of the symbol table, i.e. the layout after loading should
> be:
>     ...
> __bss_start:
>     bss space
> _end:
>     somewhat mangled ELF header
>     STRTAB/SYMTAB sections (only the STRTAB sections which are referenced by
> a SYMTAB section)
> esym:
> 
> Right now the dumpsym program extracts the mangled header and the required
> sections, we pass this in as an initrd and the kernel then copies the initrd
> to _end and initializes esym from MOD_LEN.  This is fine except that it
> needs 2 files and that's annoying.
> 
> I would add our loader to the domain builder except that it has a 4 clause
> BSD licence and I don't know if you want code in Xen which has the
> advertising clause.  The loader is in the NetBSD tree at
> sys/lib/libsa/loadfile_elf32.c.  grub also includes a loader which sets
> things up correctly...

Yes, I took a look at the GRUB code. It wouldn't be hard to add an
xc_netbsd_build() function I think. Most of the code would be in
common with the Linux builder.

> >  2. The block-device and network I/O rings are now indexed using
> >  non-wrapping counters. e.g. rather than
> >    i = (i + 1) % RING_SIZE;
> >    ent = ring[i];
> >  you do
> >    ent = ring[++i];
> >  There are predefined index types NET_RING_IDX and BLK_RING_IDX.
> 
> That's ent = ring[MASK_NET_{R,T}X_IDX(++i)], right?
> I think I'll use non-wrapping counters when writing the block-device driver
> and I'll apply the mask when accessing the ring counters...

Oops, yes!

 -- Keir


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