Re: [Qemu-devel] [PATCH 01/27] Clean up PowerPC SLB handling code

[David Gibson <david@gibson.dropbear.id.au>]

On Thu, May 19, 2011 at 08:00:53AM +0200, Andreas Färber wrote:
> Am 19.05.2011 um 07:39 schrieb David Gibson:
> 
> >On Thu, May 19, 2011 at 07:35:30AM +0200, Andreas Färber wrote:
> >>Am 25.03.2011 um 04:21 schrieb David Gibson:
> >>
> >>>Currently the SLB information when emulating a PowerPC 970 is
> >>>storeed in a structure with the unhelpfully named fields 'tmp'
> >>>and 'tmp64'.  While the layout in these fields does match the
> >>>description of the SLB in the architecture document, it is not
> >>>convenient either for looking up the SLB, or for emulating the
> >>>slbmte instruction.
> >>>
> >>>This patch, therefore, reorganizes the SLB entry structure to be
> >>>divided in the the "ESID related" and "VSID related" fields as
> >>>they are divided in instructions accessing the SLB.
> >>>
> >>>In addition to making the code smaller and more readable, this will
> >>>make it easier to implement for the 1TB segments used in more
> >>>recent PowerPC chips.
> >>>
> >>>Signed-off-by: David Gibson <dwg@au1.ibm.com>
> >>
> >>According to my bisect, this patch broke ppc64 OpenBIOS.
> >>
> >>David, would you please take a look?
> >
> >Uh, sure.  can you describe the symptoms of the breakage, and the
> >exact qemu setup you've observed the problem with?
> 
> $ uname -a
> Darwin PMG5-3.local 9.8.0 Darwin Kernel Version 9.8.0: Wed Jul 15
> 16:57:01 PDT 2009; root:xnu-1228.15.4~1/RELEASE_PPC Power Macintosh
> # Mac OS X 10.5.8 on dual-core G5
> 
> $ gcc-4.2 --version
> powerpc-apple-darwin9-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5577)
> Copyright (C) 2007 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There
> is NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.
> 
> ../qemu/configure --prefix=/Users/andreas/QEMU/latest64 \
> --target-list=ppc-softmmu,ppc64-softmmu \
> --extra-cflags="-arch ppc64" --extra-ldflags="-arch ppc64" --cc=gcc-4.2
> --host-cc=gcc-4.2 \
> --enable-cocoa --disable-kvm --disable-strip --disable-docs
> --enable-io-thread $*
> # I/O thread doesn't matter
> 
> /Users/andreas/QEMU/qemu64/ppc64-softmmu/qemu-system-ppc64 -boot d -cdrom
> /Users/andreas/QEMU/AIX/dvd.1022A4_OBETA_710.iso \
> -bios /Users/andreas/QEMU/OpenBIOS/openbios/obj-ppc64/openbios-qemu.elf
> -m 1024 \
> -M mac99 -prom-env 'auto-boot?=false' -nographic
> 
> CD should be irrelevant, -boot c -hda /dev/null should work the same.

Um, yeah, I thought putting an AIX dvd into a Mac was a bit odd.

> Expected: OpenBIOS banner and > prompt
> Observed: DSI exception on mtmsrd, no serial output

Does this happen only with your openbios image, or does it also happen
with the one included in qemu?

My working theory is that openbios is using the old 32-64 bridge stuff
where segment register accesses are emulated to populate certain SLB
slots.  I have a vague recollection that I saw the code implementing
that when I was doing the cleanup and convinced myself it was not
necessary.  More information as I investigate further.

> (The regression on ppc32 AIX observed by Kenneth seems to be a
> different issue, introduced earlier.)

I don't know what that regression is; I don't read qemu-devel
exhaustively.  If you want my attention, best to CC me directly.

-- 
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