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As part of my research I'm trying to modify the linux kernel. In particular, I'm trying to separate the pages of LKM's from the base-kernel. For some book keeping, I ...
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  1. #1
    Just Joined!
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    Modifying "struct module" breaks insmod


    As part of my research I'm trying to modify the linux kernel. In particular, I'm trying to separate the pages of LKM's from the base-kernel. For some book keeping, I added a field to 'struct module' in module.h and have been experiencing problems with loading LKMs.

    I get the error:
    insmod: -1 Invalid parameters

    /var/log/messages:
    Jul 15 12:35:46 xensezer kernel: [ 199.878540] WARNING: at /home/ecsezer/kernels/linux-2.6.24/lib/kobject.c:176 kobject_add()
    Jul 15 12:35:46 xensezer kernel: [ 199.878546] Pid: 6033, comm: insmod Not tainted 2.6.24-19-generic #4
    Jul 15 12:35:46 xensezer kernel: [ 199.878548]
    Jul 15 12:35:46 xensezer kernel: [ 199.878548] Call Trace:
    Jul 15 12:35:46 xensezer kernel: [ 199.878556] [kobject_get+0x12/0x20] kobject_get+0x12/0x20
    Jul 15 12:35:46 xensezer kernel: [ 199.878563] [kobject_add+0x1ec/0x200] kobject_add+0x1ec/0x200
    Jul 15 12:35:46 xensezer kernel: [ 199.878570] [mod_sysfs_setup+0x34/0xe0] mod_sysfs_setup+0x34/0xe0
    Jul 15 12:35:46 xensezer kernel: [ 199.878573] [sys_init_module+0x1556/0x1aa0] sys_init_module+0x1556/0x1aa0
    Jul 15 12:35:46 xensezer kernel: [ 199.878581] [_atomic_dec_and_lock+0x48/0x70] _atomic_dec_and_lock+0x48/0x70
    Jul 15 12:35:46 xensezer kernel: [ 199.878584] [ext3:dput+0xbc/0x340] dput+0xbc/0x140
    Jul 15 12:35:46 xensezer kernel: [ 199.878591] [system_call+0x7e/0x83] system_call+0x7e/0x83
    Jul 15 12:35:46 xensezer kernel: [ 199.878596]


    I compile the LKM before trying to load it. Why is this happening? I appreciate any insight and/or pointers to other sources.

    Thanks,

    John

    PS. I do get some warning messages about some modules (no name) not agreeing about the size of 'struct module'. But I'm not sure if the two are related. The snippet from /var/log/messages above only happens when I try to install a module. The module loading fails but the kernel continues to run ok.

  2. #2
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    So I had given up on this problem and decided to create my own header file and data structures without changing the original declarations. However, I recently realized that some of the changes I made were not taking effect. So I think I've found the problem.

    When I modify and recompile the kernel, all the builtin modules compile with the header files I've modified. But when I install the kernel, the header files in /usr/src/linux-header-* were not updated. Therefore LKM's I compiled later were still using the original header files.

    I'm using Ubuntu Hardy and following the instructions in https://help.ubuntu.com/community/Kernel/Compile. I realized that the header files are installed in /usr/src/linux-2.6.24-19-generic and the header files are symbolic links to the real header files that are not modified. I'm not sure if this was intentional or not and I'll post on Ubuntu forums as well. Here is the output from dpkg:

    Code:
    (Reading database ... 142983 files and directories currently installed.)
    Preparing to replace linux-headers-2.6.24-19-generic 2.6.24-19.34 (using linux-headers-2.6.24-19-generic_2.6.24-19.34_amd64.deb) ...
    Unpacking replacement linux-headers-2.6.24-19-generic ...
    Setting up linux-headers-2.6.24-19-generic (2.6.24-19.34) ...

    Finally, the Makefile I'm using to compile my LKM is:
    Code:
    obj-m += test.o
    
    all:
            make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
    
    clean:
            make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
    Perhaps it is possible to change the directory so the modified header files are used instead. Yet the symbolic links even in my source directory point to /usr/src/linux-headers-*

    Cheers,

    John

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