grub / grub2 conflicts

[Matthew Garrett]

On Fri, Sep 16, 2011 at 03:01:06PM -0400, Doug Ledford wrote:
> On 9/15/2011 12:01 PM, Matthew Garrett wrote:
> > On Thu, Sep 15, 2011 at 04:56:43PM +0100, Richard W.M. Jones wrote:
> > The most obvious case where it can fail involves grub being effectively 
> > unmaintained, and so various vendors have extended it in different ways. 
> > You may end up with valid configuration files for one distribution that 
> > can't be parsed by the grub for another. The assumption you're making is 
> > fragile. It's even worse for grub2, since it has a built-in module 
> > loader. Modules built for one version of grub aren't guaranteed (or even 
> > really expected) to work when loaded into another.
> 
> No it's not.  Grub doesn't install the 1.5 stage or the 2nd stage
> loaders, it uses the ones present in the root filesystem defined by the
> install command.  In this case, that's going to be the modules in the
> guest vm filesystem.  As such, anything valid in the guest vm's copy of
> grub will work in the guest vm even if the grub used to install the
> master boot record comes from the host.

grub-install *does* install the 1.5 and 2nd stage loaders. Even if it 
didn't, I'm not convinced it's guaranteed that an arbitrary grub stage 1 
can launch an arbitrary grub stage 1.5 since there are assumptions about 
register and stack state - see start.S.

-- 
Matthew Garrett | mjg59 at srcf.ucam.org