Re: [Qemu-devel] [PATCH] sparc64: reimplement tick timers v2

[Igor Kovalenko]

On Tue, Jan 19, 2010 at 9:44 PM, Blue Swirl <address@hidden> wrote:
> On Mon, Jan 18, 2010 at 10:28 PM, Igor V. Kovalenko
> <address@hidden> wrote:
>> From: Igor V. Kovalenko <address@hidden>
>>
>> sparc64 timer has tick counter which can be set and read,
>> and tick compare value used as deadline to fire timer interrupt.
>> The timer is not used as periodic timer, instead deadline
>> is set each time new timer interrupt is needed.
>
> Does not compile:
>
>  CC    sparc64-softmmu/sun4u.o
> cc1: warnings being treated as errors
> /src/qemu/hw/sun4u.c: In function 'cpu_tick_set_count':
> /src/qemu/hw/sun4u.c:467: error: implicit declaration of function
> 'TIMER_DPRINTF'
> make[1]: *** [sun4u.o] Error 1

Sorry forgot the split out debugging piece. New v3 has all these
comments addressed.

> If I add the missing TIMER_DPRINTF, Linux still crashes:
>
> Memory: 117376k available (2136k kernel code, 664k data, 184k init)
> [fffff80000000000,0000000007e80000]
> SLUB: Genslabs=14, HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1
> Hierarchical RCU implementation.
> NR_IRQS:255
> clocksource: mult[a0000] shift[16]
> clockevent: mult[19999999] shift[32]
> Console: colour dummy device 80x25
> Unable to handle kernel NULL pointer dereference
> tsk->{mm,active_mm}->context = 0000000000000000
> tsk->{mm,active_mm}->pgd = fffff800006fdaa4
>              \|/ ____ \|/
>              "@'/ .. \`@"
>              /_| \__/ |_\
>                 \__U_/
> swapper(0): Oops [#1]
> TSTATE: 0000004480001607 TPC: 00000000006e32f4 TNPC: 00000000006e32f8
> Y: 00000000    Not tainted
> TPC: <calibrate_delay+0x94/0x2e0>

Easy to reproduce here, and I still fail to find the reason for this crash.
It looks like linux kernel loads zero values from memory while returning
from timer softirq handler. Note this does not always happen at first timer
interrupt inside calibrate_delay loop.

I really want to see debug trace of all processed instructions, but
qemu command line switch -singlestep does not really work for sparc64-softmmu
and stepping through calibrate_delay does not seem to help at the moment.
Any ideas on how to force all instructions after approx. 5000000 cpu
cycles to be
single stepped, so I get the trace in qemu.log ?

-- 
Kind regards,
Igor V. Kovalenko