Re: [Qemu-devel] Powerpc regressions?

[Alexander Graf]

Hi Rov,



On 08.07.2009, at 00:48, Rob Landley <address@hidden> wrote:

> If you grab this tarball:
>
> http://impactlinux.com/fwl/downloads/binaries/system-image/system-image-powerpc.tar.bz2
>
> Extract it, and ./run-emulator.sh.
>
> This ran fine under svn 6657 (which is git 2d18e637e5ec).  The next  
> commit screwed up openbios, but
> reverting openbios worked for a while.

I don't think there's any _real_ ppc maintainer for qemu atm.

> In the last couple months, two problems have cropped up:
>
> 1) -hda sets /dev/hdc instead of /dev/hda (which is the cdrom).
> 2) The kernel panics running init:
>
> Unable to handle kernel paging request for data at address 0x0000007c
> Faulting instruction address: 0xc0125610
> Oops: Kernel access of bad area, sig: 11 [#1]
> PowerMac
> NIP: c0125610 LR: c013ea9c CTR: c013ea88
> REGS: c7827be0 TRAP: 0300   Not tainted  (2.6.29)
> MSR: 00009032 <EE,ME,IR,DR>  CR: 42224022  XER: 00000000
> DAR: 0000007c, DSISR: 40000000
> TASK = c78257f0[1] 'init.sh' THREAD: c7826000
> GPR00: c013ea9c c7827c90 c78257f0 00000000 c7825820 00000000  
> b2f34226 00000000
> GPR08: c7822ed8 00000001 c013ea88 00000000 58389c00 100834dc 28220022 10060000
> GPR16: 10080000 100852a8 00000000 10040000 00000000 c0310000  
> c031594c c0270000
> GPR24: 00000001 c0310000 0000000a c0310000 c02ee370 00000000 00000001 00000000
> NIP [c0125610] tty_wakeup+0x14/0xa0
> LR [c013ea9c] uart_tasklet_action+0x14/0x24
> Call Trace:
> [c7827c90] [c0125630] tty_wakeup+0x34/0xa0 (unreliable)
> [c7827ca0] [c013ea9c] uart_tasklet_action+0x14/0x24
> [c7827cb0] [c00303c8] tasklet_action+0x88/0x104
> [c7827cd0] [c00304d0] __do_softirq+0x8c/0x134
> [c7827d10] [c0006ba0] do_softirq+0x58/0x5c
> [c7827d20] [c003033c] irq_exit+0x94/0x98
> [c7827d30] [c0006c40] do_IRQ+0x9c/0xc0
> [c7827d50] [c0012778] ret_from_except+0x0/0x1c
> --- Exception: 501 at uart_start+0x24/0x38
>    LR = uart_start+0x20/0x38
> [c7827e30] [c014043c] uart_write+0xc4/0xe8
> [c7827e60] [c01293a0] n_tty_write+0x1d4/0x3c4
> [c7827eb0] [c0126540] tty_write+0x180/0x268
> [c7827ef0] [c007feec] vfs_write+0xc4/0x16c
> [c7827f10] [c0080404] sys_write+0x4c/0x90
> [c7827f40] [c00120ac] ret_from_syscall+0x0/0x40
> --- Exception: c01 at 0x4803a2dc
>    LR = 0x4804c490
> Instruction dump:
> 38c00000 4bf02255 80010024 bba10014 38210020 7c0803a6 4e800020  
> 9421fff0
> 7c0802a6 bfc10008 7c7f1b78 90010014 <8003007c> 70090020 4082002c  
> 387f00d8
> Kernel panic - not syncing: Fatal exception in interrupt
>
> I note that this is the same kernel binary and same system image  
> that used to run fine, only qemu changed.
> I can try to tweak the kernel .config to work around this, but I  
> don't know what the actual problem is...

Tty_wakeup tried to access data in a NULL pointer.

You basically have two options how to debug this:

1) Find out which change in openbios broke things and figure out why.

2) Add a lot of debug code to your guest kernel to find out where the  
null pointer comes from. Perhaps reading the source suffices already.

Maybe you also have to do both :)

Good Luck!

Alex

> Suggestions?
>
> Rob
> --
> Latency is more important than throughput. It's that simple. - Linus  
> Torvalds