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Re: [Qemu-ppc] [OpenBIOS] Apple's BootX

From: James Lyons
Subject: Re: [Qemu-ppc] [OpenBIOS] Apple's BootX
Date: Wed, 31 Jan 2018 12:17:14 -0500
User-agent: Mozilla/5.0 (X11; Linux ppc; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 01/30/2018 10:47 AM, Jd Lyons wrote:

On Jan 30, 2018, at 9:10 AM, BALATON Zoltan <address@hidden> wrote:

On Mon, 29 Jan 2018, Jd Lyons via OpenBIOS wrote:
Ok, with a little help for Paul at the kvm-ppc mailing list, it seems the issue 
maybe that the BootX or more likely mach_kernel it trying to write something to 
or probe for an L3 cache.
With kvm could be but on TCG it doesn't seem that way. Enabling some SPR debug 
options in target/ppc/translate_init.c I see this (with qemu git HEAD without 
other patches):

$ ppc-softmmu/qemu-system-ppc -cpu G4 -d int
Write SPR 272 110 <= 07e00000
Read SPR 287 11f => 000c0209
Read SPR 25 019 => 07e00000
Read SPR 25 019 => 07e00000
Read SPR 287 11f => 000c0209
Raise exception at fff08978 => 00000003 (40000000)
Write SPR 273 111 <= 07df7ff0
Write SPR 274 112 <= 20000004
Read SPR 272 110 => 07e00000
Read SPR 273 111 => 07df7ff0
Read SPR 274 112 => 20000004
Read SPR 26 01a => fff08978
Read SPR 27 01b => 40000030

$ ppc-softmmu/qemu-system-ppc -cpu 7447a -d int
Write SPR 272 110 <= 07e00000
Read SPR 287 11f => 80030102
Read SPR 25 019 => 07e00000
Read SPR 25 019 => 07e00000
Read SPR 287 11f => 80030102
Raise exception at fff08978 => 0000004e (00)

So OpenBIOS gets unexpected exception very early right after reading the PVR so 
maybe it's a problem in OpenBIOS before it gets to what you're describing. Is 
this already fixed?


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It looks like in TCG mode that it tries to read these invalid spr’s


This doesn’t cause a halt, as the kernel boots.

I went ahead an added these spr's to the 74xx cpu, hoping that adding the L3CR would allow me to boot in KVM mode with -cpu host or -cpu 7447a_v1.5, but It didn't now the kernel hangs and I get the dmesg:

KVM: invalid SPR read: 1018

So I'm not doing it correctly or I'll have to do it in KVM and recompile the kernel for my host.

Here is the code I used for the L3CR, can anyone tell me a better way of doing it?

 /* L3CR */
    /* XXX : not implemented */
    spr_register(env, SPR_L3CR, "L3CR",
                 SPR_NOACCESS, SPR_NOACCESS,
                 &spr_read_generic, &spr_write_generic,

In TCG( -cpu 7447a_v1.5 without enable-kvm ) mode I no longer get invalid spr reads between BootX( Call Kernel! ) and mach_kernel .

If I set the value of the register to 0x80000000 the guest mach_kernel tries to make a write there in TCG mode, and booting halts.

So, I'm guessing that mach_kernel expects the value here to be 0x00000000, and if it isn't it tries to write something there.

In KVM mode the Kernel is unable to read the register. So I've got to figure some way around that. Or figure out why the kernel is trying to read this register for a CPU that doesn't support an L3 cache?

I don't know if this is an issue with Qemu, or the kernel reads this register when I boot native on the bare metal. Anyone know a way of getting a dump of register access on the bare metal?

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