Kernel Module with multiple source files not initializing

Irfan Ullah (울라 이르판) irfan at dke.khu.ac.kr
Wed Nov 6 20:50:25 EST 2019


Thanks a lot. it is working now.

On Wed, Nov 6, 2019 at 1:52 AM Aruna Hewapathirane <
aruna.hewapathirane at gmail.com> wrote:

> >> On Fri, Oct 25, 2019 at 5:16 AM Irfan Ullah (울라 이르판) <
> irfan at dke.khu.ac.kr> wrote:
> >> Dear All,
> >> I have developed a kernel module consists of one source file that sends
> and receives  message to the user space.  I have spitted the source code in
> two files, and now I  am trying to develop kernel module from these source
> files. After compiling >> and linking without any problems, I insmod the
> module but I didn’t see any of the printk() I wrote, in fact, the module
> can be inserted and removed, but it does nothing. Code is in the attached
> file zipped file.
> >> I tried many things , e.g.,  link <https://paguilar.org/?p=7>1, link2
> <https://www.linuxquestions.org/questions/linux-kernel-70/kernel-module-with-multiple-source-files-not-initializing-886190/>,
> and link3
> <https://android.googlesource.com/kernel/msm/+/android-msm-dory-3.10-kitkat-wear/Documentation/kbuild/modules.txt> etc.
> but nothings worked out.
> >> I also used *nm* to inspect the module, but, as expected, there was no
> signs of "__init and __exit" functions can in the output.
>
> When you take a careful look at make's output we see that
> netlink_kernel_module.c
> is not being compiled. See below:
>
> aruna at debian:~/Downloads/kmod6$ make
> make -C /lib/modules/3.16.0-4-amd64/build M=/home/aruna/Downloads/kmod6
> modules
> make[1]: Entering directory '/usr/src/linux-headers-3.16.0-4-amd64'
> make[1]: Entering directory `/usr/src/linux-headers-3.16.0-4-amd64'
>   CC [M]  /home/aruna/Downloads/kmod6/netlink_kernel_space.o
>   LD [M]  /home/aruna/Downloads/kmod6/netlink_kernel_module.o
>   Building modules, stage 2.
>   MODPOST 1 modules
>   CC      /home/aruna/Downloads/kmod6/netlink_kernel_module.mod.o
>   LD [M]  /home/aruna/Downloads/kmod6/netlink_kernel_module.ko
> make[1]: Leaving directory '/usr/src/linux-headers-3.16.0-4-amd64'
>
> This is why nm does not show hello_init or hello_exit.
>
> >> Can you please help me: what's the problem/mistake I am doing?
>
> Change your Makefile so the module name is not the same as the C source
> file. Let's say
> we want the module to be named aruna.ko ( make up any name different to
> the C source file)
>
> obj-m := aruna.o
> aruna-objs := netlink_kernel_module.o netlink_kernel_space.o
>
> and now make shows:
>
> make -C /lib/modules/3.16.0-4-amd64/build
> M=/home/aruna/kmod6/Kernel_User_comm modules
> make[1]: Entering directory '/usr/src/linux-headers-3.16.0-4-amd64'
> make[1]: Entering directory `/usr/src/linux-headers-3.16.0-4-amd64'
>   CC [M]  /home/aruna/kmod6/Kernel_User_comm/netlink_kernel_module.o  //
> <-- THIS TIME IT COMPILES !
>   CC [M]  /home/aruna/kmod6/Kernel_User_comm/netlink_kernel_space.o
>   LD [M]  /home/aruna/kmod6/Kernel_User_comm/aruna.o
>   Building modules, stage 2.
>   MODPOST 1 modules
>   CC      /home/aruna/kmod6/Kernel_User_comm/aruna.mod.o
>   LD [M]  /home/aruna/kmod6/Kernel_User_comm/aruna.ko
> make[1]: Leaving directory '/usr/src/linux-headers-3.16.0-4-amd64'
>
> and now nm aruna.ko shows:
> aruna at debian:~/kmod6/Kernel_User_comm$ nm aruna.ko
> 0000000000000020 T cleanup_module
> 0000000000000080 T create_socket
> 0000000000000040 T data_update
>                  U __fentry__
> 0000000000000020 t hello_exit               // WE HAVE hello_exit
> 0000000000000000 t hello_init                // WE HAVE hello_init
> 0000000000000000 T init_module
> 0000000000000070 T kernel_space_receiver
> 0000000000000050 T kernel_space_sender
> 0000000000000053 r __module_depends
> 0000000000000004 D pid
>                  U printk
> 0000000000000000 D res
> 0000000000000000 D __this_module
> 0000000000000000 r __UNIQUE_ID_author2
> 0000000000000013 r __UNIQUE_ID_description1
> 0000000000000047 r __UNIQUE_ID_license0
> 000000000000005c r __UNIQUE_ID_vermagic0
> 0000000000000000 r ____versions
>
> To get make to do this smoothly you will have to fix the multiple
> definition and
> other errors I encountered along the way. And something's in your header
> file really should belong in a C file :) heed Valdis's advice.
>
> As a learning experience try this Makefile:
>
> ------------------------------------------------------------------------------------------------------
> obj-m := aruna.o
> aruna-objs := netlink_kernel_module.o netlink_kernel_space.o
>
> SHELL += -x
>
> all:
>          make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
> clean:
>         make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
>
> ------------------------------------------------------------------------------------------------------
>
> One simple way to enhance the output of GNU Make is to redefine SHELL.
> SHELL is a GNU Make built-in variable that contains the name of the shell
> to use when
> GNU Make executes commands.
>
> Reference:
> https://www.cmcrossroads.com/article/tracing-rule-execution-gnu-make
>
> Since most shells have a -x option that causes them to print out each
> command they
> are about to execute modifying SHELL in a Makefile by appendin -x causes
> every command
> to be printed (usually preceded by +) as the Makefile is run.
>
> Try:
> make clean the make and go through the output can be an enlightening
> experience.
>
> Ah the joys of building a kernel module that has more than one source file
> :-)--
>
> Good luck - Aruna
>
>

-- 
*Best Regards,*


*Mr. Irfan Ullah*
PhD Candidate
Data and Knowledge Engineering(DKE) Lab
Department of Computer Science and Engineering
Kyung Hee University, South Korea.
 +82-010-591-51651 <+82%2010-3877-8867>
  sahibzada.iu at gmail.com
 sahibzada_irfanullah
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