Re: [Qemu-devel] (i386) TCG is broken in 1.5-rc0 with guest kernel 3.2?

[Michael Tokarev <mjt@tls.msk.ru>]

08.05.2013 12:22, Michael Tokarev wrote:
> Something strange is going on here.
> 
> I just tried 1.5-rc0 (32bit x86 userspace), and guest kernel
> crashes in an interesting way right at init time.
> 
>  qemu-system-x86_64 -net none -kernel /boot/vmlinuz-3.2-amd64 -append console=ttyS0 -serial file:serial
> 
> This results in:
> 
> [    0.071315] mce: CPU supports 10 MCE banks
> [    0.082316] SMP alternatives: switching to UP code
> [    0.658457] Freeing SMP alternatives: 16k freed
> [    0.660716] ACPI: Core revision 20110623
> [    0.744749] ..TIMER: vector=0x30 apic1=0 pin1=2 apic2=-1 pin2=-1
> [    0.778545] CPU0: AMD QEMU Virtual CPU version 1.4.90 stepping 03
> [    0.887450] Performance Events: Broken PMU hardware detected, using software events only.
> [    0.889372] NMI watchdog disabled (cpu0): hardware events not enabled
> [    0.889372] Brought up 1 CPUs
> [    0.889372] Total of 1 processors activated (6432.01 BogoMIPS).
> [    0.889372] devtmpfs: initialized
> [    0.889372] ------------[ cut here ]------------
> [    0.889372] WARNING: at fs/sysfs/group.c:138 dpm_sysfs_add+0xb4/0xc0()
> [    0.889372] Hardware name: Bochs
> [    0.889372] sysfs group ffffffff814bece0 not found for kobject 'platform'
...


This is broken by the following:

commit 57eb0cc85469a8948d1036ab830951e63aa32f66
Author: Richard Henderson <rth@twiddle.net>
Date:   Wed Jan 16 11:00:14 2013 -0800

    target-i386: expand cmov via movcond

    Signed-off-by: Richard Henderson <rth@twiddle.net>


After this change, (at least) 3.2 kernel starts behaving badly,
being unable to boot in qemu TCG mode:

> The same happens with other 3.2.x kernels, for example, ubuntu precise:
> http://archive.ubuntu.com/ubuntu/dists/precise/main/installer-amd64/current/images/netboot/ubuntu-installer/amd64/linux
> 
> 
> qemu-system-x86_64 from qemu-1.4.x lets these kernels to boot fine,
> it all boots fine when adding -enable-kvm.  So it is some change(s)
> in TCG between 1.4 and 1.5, maybe triggering a bug in guest kernel.
> 
> For added fun, for example, 3.8 guest kernel does NOT have problems
> with this config.


I'm trying 64bits now too...

/mjt