Compiling Linux Kernel Module With A Custom Header

Question

I would like to compile a simple character device module depending on a custom header. The folder is thus organized,

+ mymod.c
| customized-header.h
| customized-header.c
| Makefile

In mymod.c, the header is thus used,

#include "customized-header.h"

In Makefile:

obj-m := mymod.o
mymod-objs := customized-header.o
KVERSION = $(shell uname -r)
PWD = $(shell pwd)
all:
    make -C /lib/modules/$(KVERSION)/build M=$(PWD) modules
clean:
    make -C /lib/modules/$(KVERSION)/build M=$(PWD) clean

Everything should work fine, the module gets compiled without problem, I can load the module through sudo insmod, but the module doesn't work properly. When I checked nm mymod.ko, there are a lot of vars and functions are missing. It looks as if it stopped after linking customized_header.o. If I remove this header and its function, say no header function calls from the module, it compiles perfectly with desired result.

Could you see what went wrong here?

What happens when you change the obj-m line to: obj-m := mymod.o customized-header.o? — Peter L.
– Peter L., Commented Oct 1, 2013 at 23:00
@PeterL. Well, obj-m is to generate a module. When I added customized-header.o, some more files are generated: like customized-header.ko. In the meantime, mymod.ko is still the same. Here I would like only one module, which is mymod.ko, the customized-header works like a library for the module. — MeadowMuffins
– MeadowMuffins, Commented Oct 2, 2013 at 11:41

Community · Accepted Answer · 2017-05-23 12:13:05Z

3

The problem resides in the Makefile. Due to the link here, I changed it into

obj-m: mymodko.o
mymodko-obj: customized-header.o mymod.o

It now works fine. So the question was the naming of module object. We need to specify different names as in this case mymodko.o and mymod.o.

edited May 23, 2017 at 12:13

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answered Oct 2, 2013 at 12:20

MeadowMuffins

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1 Comment

MeadowMuffins Over a year ago

@BenjaminLeinweber I need to wait for another 20 hours to accept my own answer.

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