ldd3 project

LDD3 project

Add the linux kernel source

Please execute the following command with the root privilege.

# apk add linux-lts-dev

Get the project source

% cd ~/proj
% git clone https://github.com/martinezjavier/ldd3.git
% cd ldd3

export the KERNELDIR

% export KERNELDIR=/lib/modules/5.10.29-0-lts/build/

Why we need the above KERNELDIR? If you check the Makefile in misc-modules directory. You will find the how the script setup the KERNELDIR. On some system the Makefile is smart to determine the kernel directory. On this IDE, for uname -r docker returns 5.10.25-linuxkit, while alpine linux-lts-dev returns 5.10.29-0-lts. Amazing?

# To build modules outside of the kernel tree, we run "make"
# in the kernel source tree; the Makefile these then includes this
# Makefile once again.
# This conditional selects whether we are being included from the
# kernel Makefile or not.

LDDINC=$(PWD)/../include
EXTRA_CFLAGS += -I$(LDDINC)

ifeq ($(KERNELRELEASE),)

    # Assume the source tree is where the running kernel was built
    # You should set KERNELDIR in the environment if it's elsewhere
    KERNELDIR ?= /lib/modules/$(shell uname -r)/build
    # The current directory is passed to sub-makes as argument
    PWD := $(shell pwd)

modules:
        $(MAKE) -C $(KERNELDIR) M=$(PWD) modules

modules_install:
        $(MAKE) -C $(KERNELDIR) M=$(PWD) modules_install

clean:
        rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions *.mod modules.order *.symvers

.PHONY: modules modules_install clean

else
    # called from kernel build system: just declare what our modules are
    obj-m := hello.o hellop.o seq.o jiq.o sleepy.o complete.o \
             silly.o faulty.o kdatasize.o kdataalign.o jit.o
endif

Make with bear

The following is one example to generate compile_commands.json. Here, bear will run make as usual and generate compile_commands.json in the current directory.

We also run make clean to show the result clearly. Please note the generated compile_commands.json file.

% cd ~/proj/ldd3/scullc
% bear -- make
make -C /lib/modules/5.10.29-0-lts/build M=/home/ide/proj/ldd3/scullc modules
make[1]: Entering directory '/usr/src/linux-headers-5.10.29-0-lts'
  CC [M]  /home/ide/proj/ldd3/scullc/main.o
  CC [M]  /home/ide/proj/ldd3/scullc/scull-shared/scull-async.o
  LD [M]  /home/ide/proj/ldd3/scullc/scullc.o
  MODPOST /home/ide/proj/ldd3/scullc/Module.symvers
  CC [M]  /home/ide/proj/ldd3/scullc/scullc.mod.o
  LD [M]  /home/ide/proj/ldd3/scullc/scullc.ko
make[1]: Leaving directory '/usr/src/linux-headers-5.10.29-0-lts'
% make clean
$ ls 
Makefile               main.c                 scull-shared           scullc_load
compile_commands.json  mmap.c                 scullc.h               scullc_unload

Edit source file

Now you can edit the any source file under scullc directory. You can also try misc-modules directory to repeat the above process.

From the above example, Generate the compile_commands.json file with bear is easy.