Re: [uml-devel] kernel module support broken on x86-64?

[juergen.kadidlo@exasol.com]

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Boaz Harrosh wrote:

>juergen.kadidlo@exasol.com wrote:
>  
>
>>Boaz Harrosh wrote:
>>    
>>
>>>juergen.kadidlo@exasol.com wrote:
>>>  
>>>      
>>>
>>>>Boaz Harrosh wrote:
>>>>    
>>>>        
>>>>
>>>>>juergen.kadidlo@exasol.com wrote:
>>>>>  
>>>>>      
>>>>>          
>>>>>
>>>>>>Hi!
>>>>>>
>>>>>> I've compiled an UML kernel based on 2.6.25 but loading kernel modules 
>>>>>>seems to be broken. No matter which module I try to load the output 
>>>>>>looks similar to this:
>>>>>>
>>>>>> overflow in relocation type 11 val 80836d41
>>>>>>'loop' likely not compiled with -mcmodel=kernel
>>>>>>
>>>>>>After searching for a while I found some threads from 2006 discussing 
>>>>>>this issue, e.g.:
>>>>>>http://www.mail-archive.com/user-mode-linux-devel@lists.sourceforge.net/msg03693.html
>>>>>>and
>>>>>>http://marc.info/?l=user-mode-linux-devel&m=115125101012707&w=2
>>>>>>
>>>>>>As Andi Kleen has mentioned in a mail from the first thread, simply 
>>>>>>appending "-mcmodel=kernel" to the KBUILD_CFLAGS does not work (I tried 
>>>>>>it anyway and can confirm his statement ;)
>>>>>>
>>>>>>Since I could not find any solution I've decided to write this mail and 
>>>>>>ask about the current state of this issue and of course for a solution! 
>>>>>>I simply don't want to believe that there is no loadable module support 
>>>>>>for UML in 2008...
>>>>>>
>>>>>>Regards
>>>>>>JK
>>>>>>
>>>>>>    
>>>>>>        
>>>>>>            
>>>>>>
>>>>>Every thing is fine down here. What host Kernel-gcc-glibc / uml-gcc-glibc
>>>>>are you using?
>>>>>
>>>>>I'm using out-of-tree modules with uml for every kernel since 2.6.19.
>>>>>I have both Host and UML as x86_64 on FC7 with gcc 4.1.2
>>>>>
>>>>>Boaz
>>>>>
>>>>>  
>>>>>      
>>>>>          
>>>>>
>>>>I'm glad to here that the bug has been fixed. Anyway, it does not work
>>>>with my configuration:
>>>>
>>>> - CentOS 5.1 as host system and UML root fs
>>>> - Kernel 2.6.25.4 (vanilla, but config taken from the CentOS kernel)
>>>> - GCC 4.1.2
>>>> - GLIBC 2.5
>>>>
>>>>Regards
>>>>JK
>>>>
>>>>    
>>>>        
>>>>
>>>I used to run with red-hat 4.5 so this should work.
>>>64 bit, right?
>>>
>>>From passed experience I've seen that UML will only
>>>work if I first do "make ARCH=um defconfig"  and then
>>>manually enable any needed options with make xconfig.
>>>other wise it breaks in all kind of ways. Even doing
>>>a make oldconfig on a good uml config file from older
>>>kernel will not work. Try to do defconfig and see if
>>>it loads at all.
>>>
>>>How do you compile and run the out-of-tree module
>>>or is it one of the built in modules?
>>>
>>>Boaz
>>>
>>>  
>>>      
>>>
>>I tried what you've suggested and did the following:
>>- make mrproper
>>- make defconfig ARCH=um
>>- make linux ARCH=um
>>- make modules ARCH=um
>>- make modules_install INSTALL_MOD_PATH=/path/to/mounted/uml_root_fs ARCH=um
>>
>>It did not work (same result).
>>
>>After that, I copied the kernel source to the uml-root-fs, started the
>>UML and did a 'make clean' and 'make modules ARCH=um' inside the running
>>UML, followed by a 'make modules_install'. Again, it did not work.
>>
>>After that, I've extracted the kernel source again (completely vanilla)
>>and restarted at 'make defconfig'. Same result.
>>No module is loadable. They all have 'invalid fomrat' an the usage of
>>the '-mcmodel=kernel' flag is suggested.
>>
>>BTW : with the same sources (and the same commands as listed above) I've
>>successfully built a fully working 32 bit UML kernel!
>>
>>I've also tried kernel 2.6.24.7 with identical results.
>>
>>Last but not least, I've tried the same with a fresh download of the
>>2.6.26 kernel. Unfortunately, this time there was another problem: the
>>kernel exits with a panic on startup (tried to build it twice with the
>>same result). According to the stack-trace, the panic happens somewhere
>>inside "get_page_from_free_list()"...
>>
>>I'm really running out of ideas right now, does anyone have some
>>suggestions?
>>
>>Regards
>>JK
>> 
>>    
>>
>
>It all works down here. Just a long shot you have installed uml_utilities
>on the host ...
>  
>
They are installed.

>I run the uml from the root of the source tree like this:
>.../.build_um/vmlinux ubd0=/usr0/var/local/um/Fedora7-AMD64-root_fs eth0=tuntap,,,192.168.0.117 mem=256M
>(The .build_um/ is because I use KBUILD_OUTPUT=.build_um so I can compile 
>multiple targets from same source tree)
>
>Maybe there is some package missing from the Linux image you are using.
>You are using a 64bit Linux image with your 64bit kernel, yes?
>Try to compare the 32 bit image with the 64bit one. See if they have
>the same packages installed. I started with a ready made fedora7 uml
>image and never really touched it much except the occasional yum install
>of a library or two.
>
>Boaz
>  
>
I already thought about the root fs being the reason for this, but I 
can't imagine how a different root can affect the kernel's ability to 
load modules. It should not be affected by any packages installed, isn't it?
 Anyway, after taking a closer look to your starting command, I noticed 
another difference: I've always been using "mem=512m" on the 64 bit 
system (it's an 8 GB machine). I've tried it with "mem=256" and IT 
FINALLY WORKS! All the kernels I've compiled are working correctly now, 
except for the 2.6.26 which still exits with a panic on startup...

Thank you very much for your help! But I'd really like to know why it 
did not work with "m= 512m". I've always thought that this would only 
alter the max. available memory inside the UML. Maybe this is a bug though?

Regards
JK

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