Re: [SeaBIOS] [Qemu-devel] [Qemu-stable] problems with freeBSD

[Kevin O'Connor]

On Fri, Mar 08, 2013 at 12:03:15AM +0800, Peter Maydell wrote:
> Earlier in this thread it's been stated that this often produces
> subtly broken blobs...

I think there have been some far reaching conclusions in this thread
based on incorrect premises.

SeaBIOS has had problems with mis-compilations in the past.  To handle
this, the SeaBIOS build runs test cases on every compilation to verify
the tool chain (see tools/test-build.sh).  I have not seen a report of
a guest visible SeaBIOS mis-compilation in many years.

There have been a few cases of guest bugs that get tickled when
changes to SeaBIOS cause slightly different memory layouts.  The last
case of this that comes to mind is the JunOS bug that was tracked down
a year and a half ago.  The root cause of the FreeBSD issue raised in
this thread is very similar - the full details aren't known yet, but
we do know that a slightly different memory layout is ticking a bug in
a FreeBSD page presence check.

Since changes are inevitable anyway (the only alternative would be to
never enhance SeaBIOS), I don't believe that dictating one "true
compiler" or one "true blob" is necessary or desirable.

-Kevin

[Qemu-devel] [Qemu-stable] problems with freeBSD

[Peter Stuge]

Kevin O'Connor wrote:
> I don't believe that dictating one "true compiler" or one "true
> blob" is necessary or desirable.

Sure. The point isn't to have only one correct way, but to have
reliable results in the common case.

A reference toolchain and a reference blob both help accomplish
that, but they're by no means the only, or even best, methods.

//Peter