[Qemu-devel] [PATCH] s390: remove boot image detection to fix boot with newer kernels

[Qemu-devel] [PATCH] s390: remove boot image detection to fix boot with newer kernels

[Christian Borntraeger]

Alex,

Newer kernels will not always have a 0dd0 (basr 13,0) at address 0x10000.
(e.g. current linux-next). We must not rely on specific code at certain
addresses, so lets just remove this check.

Reported-by: Philipp Muens <programming.philipp.muens@googlemail.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

---
 hw/s390-virtio.c |    5 -----
 1 file changed, 5 deletions(-)

Index: b/hw/s390-virtio.c
===================================================================
--- a/hw/s390-virtio.c
+++ b/hw/s390-virtio.c
@@ -193,11 +193,6 @@ static void s390_init(ram_addr_t my_ram_
     if (kernel_filename) {
         kernel_size = load_image(kernel_filename, qemu_get_ram_ptr(0));
 
-        if (lduw_be_phys(KERN_IMAGE_START) != 0x0dd0) {
-            fprintf(stderr, "Specified image is not an s390 boot image\n");
-            exit(1);
-        }
-
         env->psw.addr = KERN_IMAGE_START;
         env->psw.mask = 0x0000000180000000ULL;
     } else {

Re: [Qemu-devel] [PATCH] s390: remove boot image detection to fix boot with newer kernels

[Alexander Graf]

On 06.09.2011, at 13:41, Christian Borntraeger wrote:

> Alex,
> 
> Newer kernels will not always have a 0dd0 (basr 13,0) at address 0x10000.
> (e.g. current linux-next). We must not rely on specific code at certain
> addresses, so lets just remove this check.

Is there any other sane way we can find out if the image we're loading is actually bootable? I don't want users to do qemu-system-s390x -kernel vmlinux and see it just plain fail.


Alex

Re: [Qemu-devel] [PATCH] s390: remove boot image detection to fix boot with newer kernels

[Christian Borntraeger]

On 07/09/11 13:56, Alexander Graf wrote:
> 
> On 06.09.2011, at 13:41, Christian Borntraeger wrote:
> 
>> Alex,
>>
>> Newer kernels will not always have a 0dd0 (basr 13,0) at address 0x10000.
>> (e.g. current linux-next). We must not rely on specific code at certain
>> addresses, so lets just remove this check.
> 
> Is there any other sane way we can find out if the image we're loading is 
> actually bootable? I don't want users to do qemu-system-s390x -kernel 
> vmlinux and see it just plain fail.

No, in theory it could change arbitrarily. The vmlinux case is unfortunate
but in the end its "shoot yourself in the foot", we just have to make sure
that we allow a graceful exit from a looping qemu guest.


Christian

Re: [Qemu-devel] [PATCH] s390: remove boot image detection to fix boot with newer kernels

[Alexander Graf]

On 07.09.2011, at 14:33, Christian Borntraeger wrote:

> On 07/09/11 13:56, Alexander Graf wrote:
>> 
>> On 06.09.2011, at 13:41, Christian Borntraeger wrote:
>> 
>>> Alex,
>>> 
>>> Newer kernels will not always have a 0dd0 (basr 13,0) at address 0x10000.
>>> (e.g. current linux-next). We must not rely on specific code at certain
>>> addresses, so lets just remove this check.
>> 
>> Is there any other sane way we can find out if the image we're loading is 
>> actually bootable? I don't want users to do qemu-system-s390x -kernel 
>> vmlinux and see it just plain fail.
> 
> No, in theory it could change arbitrarily. The vmlinux case is unfortunate
> but in the end its "shoot yourself in the foot", we just have to make sure
> that we allow a graceful exit from a looping qemu guest.

That's not the answer I'd like to hear. Can't we put a magic constant somewhere for newer kernel versions that would identify those and keep the basr 13,0 hack around for older ones?


Alex

Re: [Qemu-devel] [PATCH] s390: remove boot image detection to fix boot with newer kernels

[Christian Borntraeger]

On 07/09/11 14:34, Alexander Graf wrote:
>> No, in theory it could change arbitrarily. The vmlinux case is unfortunate
>> but in the end its "shoot yourself in the foot", we just have to make sure
>> that we allow a graceful exit from a looping qemu guest.
> 
> That's not the answer I'd like to hear. Can't we put a magic constant somewhere
>for newer kernel versions that would identify those and keep the basr 13,0 hack 
> around for older ones?

I will wire up the elf loader for s390, to make vmlinux simply work. That should
make the test no longer needed. 
There are some small problems left, e.g. the elf loader loads the kernel as bios 
afterwards and therefore overwrites the kernel parameter line. Will fix this in the
next days.

Christian