I have a LKM named RtmNetlinkLKM.c and compiles and run fine. The moment I update its Makefile to compile with other src files, it starts giving warning:
WARNING: modpost: missing MODULE_LICENSE()
The following MODULE_LICENSE("GPL"); is already present in kernel module file.
Previous Makefile, module compiles fine
obj-m += RtmNetlinkLKM.o
all:
make -C /lib/modules/`uname -r`/build M=$(PWD) modules
clean:
make -C /lib/modules/`uname -r`/build M=$(PWD) clean
updated Makefile, module now compiles with a warning
obj-m += RtmNetlinkLKM.o
RtmNetlinkLKM-objs += rt_kern.o gluethread/glthread.o << Added two more sources
all:
make -C /lib/modules/`uname -r`/build M=$(PWD) modules
clean:
make -C /lib/modules/`uname -r`/build M=$(PWD) clean
rm -f rt_kern.o
rm -f gluethread/glthread.o
When compiled using second Makefile, it gives stated warning. When I add MODULE_LICENSE("GPL") in gluethread/glthread.c , warning goes away. I don't understand, why do I need to add "GPL" license in glthread.c when it is not a module but contain functions to be used by module (It is a linked list mini-library). Why doesn't it complain with other src file rt_kern.c in a similar way. I had never made any changes in original module file RtmNetlink.c throughout this process.
Thanks to #Gautham Kantharaju in link provided by #Tsyvarev for solving my problem. While compiling multiple source files into a single module, the main reason for the warning seems to be, ".. it is not possible to have the module name and the source name to be the same."
If anyone else has the same question, I think following Makefile should solve the issue.
# give your module a different Name
obj-m += newModuleName.o
newModuleName-objs += RtmNetlinkLKM.o rt_kern.o gluethread/glthread.o
all:
make -C /lib/modules/`uname -r`/build M=$(PWD) modules
clean:
make -C /lib/modules/`uname -r`/build M=$(PWD) clean
Related
I'm trying to link a kernel module to a non-LKM source file. The problem is, I'm running into some issues. The names of the two files are chardev.c (the LKM) and foo.c.
My Makefile:
obj-m += chardev.o
obj-y += foo.o
all:
make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules
$(CC) test.c -o test
clean:
make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) clean
rm test
Inside of chardev.c I've the following line of code: extern int foo;, and inside foo I've the following line of code: int foo = 123;. (Both lines are at file-scope.)
When running make I'm getting the following output:
make -C /lib/modules/4.4.0-31-generic/build/ M=/home/kylemart/Desktop/Device-Driver modules
make[1]: Entering directory `/usr/src/linux-headers-4.4.0-31-generic'
CC [M] /home/kylemart/Desktop/Device-Driver/chardev.o
Building modules, stage 2.
MODPOST 1 modules
WARNING: "foo" [/home/kylemart/Desktop/Device-Driver/chardev.ko] undefined!
CC /home/kylemart/Desktop/Device-Driver/chardev.mod.o
LD [M] /home/kylemart/Desktop/Device-Driver/chardev.ko
make[1]: Leaving directory `/usr/src/linux-headers-4.4.0-31-generic'
cc test.c -o test
Seems things aren't linking properly. What am I doing wrong?
EDIT:
This seems to work, but there's a problem:
obj-m += chardev.o
chardev-objs += foo.o
all:
make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) modules
$(CC) test.c -o test
clean:
make -C /lib/modules/$(shell uname -r)/build/ M=$(PWD) clean
rm test
Although it compiles without warnings, after installing the compiled module (i.e. sudo insmod chardev.ko) there isn't a new device present in /dev. Previously, without trying to link source files, installing kernel modules as previously stated created a device file. That said, the device is present when running lsmod.
Your all target builds only the module, but not the kernel so that the foo symbol does not exist there.
When compiling a source (here: foo.c) into the kernel, you have to integrate the makefile into the kernel source. E.g. you have to add
obj-y += my-driver/
to the makefile in the previous directory and build the whole kernel. You should probably remove your all: and clean: targets from the makefile to avoid conflicts with kernel builtin rules.
foo.c must contain
EXPORT_SYMBOL(foo);
or
EXPORT_SYMBOL_GPL(foo);
The second makefile...
will generate only the chardev.ko module which is built from only foo.c; chardev.c will not be used for it. When you really want this, you have to change file names; e.g.
obj-m += chardev.o
chardev-objs = chardev-core.o foo.o
Is it possible to provide an output folder when building a kernel module?
These questions are very similar to mine but the answers are non conclusive Link1, Link2 (I have tested these proposals without success).
I have the following project structure and would like to put all outputs from the compiling of the kernel module into the build folder.
Makefile
src/
-main.c
build/
This is my current Makefile:
# name of the module to be built
MODULE_NAME ?= test_module
BASE := .
# define all module sources
SRCS := \
src/main.c
# extract required object files
OBJ_SRCS := $(SRCS:.c=.o)
# define path to directories containing header files
INCLUDE_DIRS = \
-I$(src)/src
# Products from the 'make all' command should be placed in this folder
BUILD_DIR := $(BASE)/build
# ccflags to pass at compile time
ccflags-y := \
$(INCLUDE_DIRS)
# setup kbuild stuff
obj-m += $(MODULE_NAME).o
$(MODULE_NAME)-y := $(OBJ_SRCS)
$(MAKE) = make
KERNEL_DIR=/lib/modules/$(shell uname -r)/build
all:
$(MAKE) -C $(KERNEL_DIR) M=$(PWD) modules
clean:
$(MAKE) -C $(KERNEL_DIR) M=$(PWD) clean
I have tried to add O=$(BUILD_DIR) as (as stated in the link above without success).
$(MAKE) -C $(KERNEL_DIR) O=$(BUILD_DIR) M=$(PWD) modules
Can anyone confirm if it is possible to redirect to output(the files generated during the compilation) when compiling the kernel module or not? (A suggestion would be much appreciated)
Is the only solution to put the Makefile in the build folder and update the all paths in the Makefile?
Thanks!
I am trying to compile a module against any source tree on the file system but I am having trouble with the Makefile. This was the original Makefile I had against the kernel specified:
obj-m += new-mod.o
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
This Makefile would compile correctly, but goal is to have it compile against any source tree. I have tried just:
obj-m += new-mod.o
I thought that "all:" is assumed but I get error:
make: *** No targets. Stop.
I have also added:
all:
to the Makefile with no difference except for error message:
make: Nothing to be done for `all'
I have tried a lot of documentation but no luck. I would greatly appreciate any help.
goal is to have it compile against any source tree
ya you can do it providing a compiled source-code path
just replace make -C /lib/modules/$(shell uname -r)/build M=$PWD modules
with this
make -C <path-to-compiled-src-code> M=$PWD modules
make -C /home/vinay/linux-3.9 M=$PWD modules
try below makefile
Makefile –
# if KERNELRELEASE is defined, we've been invoked from the
# kernel build system and can use its language.
ifneq (${KERNELRELEASE},)
obj-m := new-mod.o
# Otherwise we were called directly from the command line.
# Invoke the kernel build system.
else
KERNEL_SOURCE := /usr/src/linux
PWD := $(shell pwd)
default:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} modules
clean:
${MAKE} -C ${KERNEL_SOURCE} SUBDIRS=${PWD} clean
endif
In above you can change KERNEL_SOURCE := /usr/src/linux-->to.--> your sr-code KERNEL_SOURCE := <path to compiled-src-code>
for further info find below liks
while building kernel modules why do we need /lib/modules?
A simple program on linux device driver
How to make a built-in device driver in linux
Build against your custom kernel source ( not the one that is installed),
You can use following steps.
1.download kernel from kernel.org (tar)
2.Extract
3.make x86_64_defconfig
4.make prepare
5.make modules_prepare
Now you have to change Makefile to point to kernel source you had downloaded and extracted. Something similar mentioned in example by Vinay Answer.
Just remember you cannot insmod this module as kernel running and module built is for different kernel.
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?
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.
I'm trying to be able to execute "make debug" at the command line and it will build my driver module with the -DDEBUG_OUTPUT define, which will cause certain sections of code to be compiled in.
In 2.4 kernel makefiles, this is pretty easy. I just create a debug: target and included "-DDEBUG_OUTPUT" in the cc compilation command arguments for that target. Easy.
Unfortunately (for me), 2.6 completely changed how modules are compiled, and I can ONLY seem to find the trivial "all" and "clean" examples, which don't show adding custom defines at compilation time.
I tried this:
debug:
make -C $(KERNEL_DIR) SUBDIRS='pwd' -DDEBUG_OUTPUT modules
and got a complaint from make.
I've also tried:
.PHONY: debug
debug:
make -C $(KERNEL_DIR) SUBDIRS='pwd' EXTRA_CFLAGS="$(EXTRA_CFLAGS) -DDEBUG_OUTPUT" modules
but it is not seeing what EXTRA_CFLAGS contains. I can see from the command line output that it does correctly append the -D onto the existing EXTRA_CFLAGS, which includes the -I for includes dir. However, the driver file won't compile now because it cannot find the includes dir...so somehow it is not seeing what EXTRA_CFLAGS contains.
A "-D" option is not meant to be passed to make: it is a C preprocesseor (cpp) option.
To define DEBUG_OUTPUT for your build you have to add the following line to your Kbuild file:
EXTRA_CFLAGS = -DDEBUG_OUTPUT
Afterwards you can call, as usual:
make -C $(KERNEL_DIR) M=`pwd`
EDIT: If you don't want to edit the Kbuild file, you can have a debug target like this:
INCLUDES="-Imy_include_dir1 -Imy_include_dir2"
.PHONY: debug
debug:
$(MAKE) -C $(KDIR) M=`pwd` EXTRA_CFLAGS="$(INCLUDES) -DDEBUG_OUTPUT"
EDIT#2:
MY_CFLAGS=-DFOO -DBAR -Imydir1
all:
$(MAKE) -C $(KDIR) M=`pwd` EXTRA_CFLAGS="$(MY_CFLAGS)"
debug: MY_CFLAGS+=-DDEBUG_OUTPUT
debug:
$(MAKE) -C $(KDIR) M=`pwd` EXTRA_CFLAGS="$(MY_CFLAGS)"