Re: [Qemu-devel] PreP kernels boot using Qemu

[Aurelien Jarno]

J. Mayer a écrit :
> On Mon, 2007-10-22 at 18:28 +0200, Aurelien Jarno wrote:
>> On Mon, Oct 22, 2007 at 09:36:07AM +0200, J. Mayer wrote:
>>> Hi all,
>>>
>>> I've been investigating more about PreP kernel boot using Qemu and I
>>> achieved to boot 2.4.35, 2.6.12 and 2.6.22 kernels using Qemu CVS and
>>> unmodified OHW.
>>> The issues I found in the kernel are:
>>> - the OpenFirmware video console driver is broken in recent 2.4 kernels
>>> and have been removed from recent 2.6 kernel
>>> - I then decided to use the vga16fb console driver but needed to do some
>>> patches in order to make it compile properly
>>> - the CMOS RTC driver is not available for PPC architecture in 2.6
>>> kernels and need some patches in order to be usable
>>> - I discovered that the mkprep utility is bugged in 2.4.35 and 2.6.12
>>> kernels. The bugs are visible only when cross-compiling from a
>>> little-endian and/or 64 bits host.
>>> - I got issues (ie process freezing) when using the 2.6.22 kernel with
>>> HZ > 100. It seems to run properly when the system timer is set to 100
>>> Hz but this needs more tests for confirmation.
>>> - I got the 2.6.22 kernel crashing (ie kernel Oops in workqueue code)
>>> when it has no RTC available. There is no problem when the RTC is
>>> present. This is likely to be a kernel bug: when no RTC is available, it
>>> cannot calibrate its timers properly and the kernel timer seems to run
>>> very fast. Forcing (with hacks...) the timer to run at nearly real-time
>>> seems to prevent the bug to happen.
>>>
>>> I then generated some kernels that allow me to boot and use those 3
>>> kernels.
>>> Here are 3 tarballs with:
>>> - a patch to be applied to the vanilla kernel sources to fix the
>>> mentionned bugs
>>> - the .config file I used to build the kernel
>>> - the zImage.prep image
>>> <http://perso.magic.fr/l_indien/qemu-ppc/linux-tests/linux-2.4.35-prep.tar.bz2>
>>> <http://perso.magic.fr/l_indien/qemu-ppc/linux-tests/linux-2.6.12-prep.tar.bz2>
>>> <http://perso.magic.fr/l_indien/qemu-ppc/linux-tests/linux-2.6.22-prep.tar.bz2>
>>>
>>> I then run Qemu with the following command line template:
>>> ./ppc-softmmu/qemu-system-ppc -serial stdio -net nic,model=ne2k_isa -net
>>> tap -net nic,model=ne2k_pci -net tap -net nic,model=rtl8139 -net tap
>>> -cpu 604 -M prep -L pc-bios/ -hda <my_first_disk> -cdrom <my_cdrom>
>>> -kernel
>>> <src_base>/linux-<kversion>.patched/arch/ppc/boot/images/zImage.prep
>>>
>>> Hope this helps.
>>>
>> Yes, this help a lot, thanks! With your config file, I have been able to
>> build and boot a 2.6.22 kernel. I have used a Debian sid chroot.
>>
>> Here are a few remarks:
>> - The NE2000 card doesn't work for the same reason as with the powerpc
>>   architecture. The kernel patch below fixes the problem. I will send it
>>   later along with the ppc patch.
> 
> There's something else strange with the PCI ethernet devices: they got
> no IRQ assigned (as if the BIOS does not configure them properly). And
> the RTL8139 never has a mac address, never detects the PHY link, then
> there may be endianness issues in the emulation (I did not check at
> all).
> 
>> - The "floating point" problem I reported during the week-end does not
>>   exists, probably because of the switch from powerpc to ppc. I still 
>>   don't know if it is a kernel problem or a QEMU problem (or both).
> 
> There may be issues with the floating point emulation, especially if
> some kernel or programs relies on the FPSCR (floating-point status)
> register which is never updated in Qemu.
> 

Is there any technical reason behind that, or is it just a lack of time?


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