Re: [PATCH] target/ppc: fix memory dump endianness in QEMU monitor

[David Gibson]

On Tue, Dec 24, 2019 at 01:10:34PM -0300, Fabiano Rosas wrote:
> David Gibson <address@hidden> writes:
> 
> >> It looks like the hflags MSR_LE is being updated correctly with TCG. But
> >> with KVM we only touch it on system_reset
> >
> > Ah.. right.  I think to fix that we'd want an hreg_compute_hflags() at
> > the end of sucking the state out of KVM.
> >
> 
> Hm.. The hflags is a TCG thing that does not get used with KVM at all,
> except for that one bit in the monitor disas function. I'd rather keep
> it completely out of kvm_enabled code.

That's a fair point.

It doesn't look like there's any reason ppc_tr_init_disas_context()
couldn't initialize ctx->le_mode directly from the MSR rather than
hflags anyway.  If we do that, we should again be able to remove the
LE bit from hflags entirely.  I think that's the way to go.

> 
> Couldn't we perhaps make it conditional on the acceleration type?
> Using kvm_enabled() or some ifdef.
> 
> Thanks
> 
> >> (and possibly h_cede? I don't
> >> know if it is QEMU who handles it).
> >
> > It's KVM.  If we used the qemu one it would add an awful lot of
> > latency to cedes.
> >> 
> >> So I would let hflags be.
> >> 
> >> 
> >> ... Actually, I don't really know the purpose of hflags. It comes from:
> >> 
> >>   commit 3f3373166227b13e762e20d2fb51eadfa6a2d653
> >>   Author: Fabrice Bellard <address@hidden>
> >>   Date:   Wed Aug 20 23:02:09 2003 +0000
> >>   
> >>       pop ss, mov ss, x and sti disable irqs for the next instruction -
> >>       began dispatch optimization by adding new x86 cpu 'hidden' flags
> >>       
> >>       
> >>       git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@372 
> >> c046a42c-6fe2-441c-8c8c-71466251a162
> >> 
> >> Could any one clarify that?
> >
> > Not really.  It's really, really old, in the cruft bits of TCG I don't
> > much understand.
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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