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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?

Peter L.
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MeadowMuffins
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  • What happens when you change the obj-m line to: obj-m := mymod.o customized-header.o? – Peter L. Oct 01 '13 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 Oct 02 '13 at 11:41

1 Answers1

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.

Community
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MeadowMuffins
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