Learn Setting Up the Kernel Build Environment | Writing Your First Character Driver

Before you can begin writing and testing your own character device drivers, you must set up a suitable kernel build environment. Building kernel modules differs from compiling user-space programs: you interact directly with the kernel’s build system and require a set of specific files to ensure compatibility and successful compilation. The essential files you need are:

The kernel source code or at least its headers, matching the running kernel version;
A Makefile that instructs the kernel build system how to build your module;
Your kernel module source file, usually with a .c extension.

These files form the foundation for building and testing any kernel module.

Makefile.


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obj-m += simple_module.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

The Makefile shown above is a minimal example tailored for building a kernel module. It uses the obj-m variable to specify the object files to be built as modules. When you run make, it invokes the kernel’s own build system by calling make -C /lib/modules/$(shell uname -r)/build, passing the current directory as the module source location with M=$(PWD). This approach ensures your module is built against the correct kernel version and configuration, leveraging all the compatibility and dependency management provided by the kernel’s infrastructure.

simple_module.c


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#include <linux/module.h>
#include <linux/kernel.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("A simple minimal kernel module");

static int __init simple_init(void)
{
    printk(KERN_INFO "Simple module loaded\n");
    return 0;
}

static void __exit simple_exit(void)
{
    printk(KERN_INFO "Simple module unloaded\n");
}

module_init(simple_init);
module_exit(simple_exit);

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Section 2. Chapter 1

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The kernel source code or at least its headers, matching the running kernel version;
A Makefile that instructs the kernel build system how to build your module;
Your kernel module source file, usually with a .c extension.