I'm trying to compile following 'Hello World'.
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
MODULE_LICENSE("GPL");
MODULE_AUTHOR("BOBR");
MODULE_DESCRIPTION("HELLO MODULE");
MODULE_VERSION("0.10");
static char *name = "user";
module_param(name, charp, S_IRUGO);
MODULE_PARM_DESC(name, "The name to display");
static int __init hello_init(void) {
printk(KERN_INFO "HEllo, %s!\n", name);
return 0;
}
static void __exit hello_exit(void) {
printk(KERN_INFO "Goodbye, %s !\n", name);
}
module_init(hello_init);
module_exit(hello_exit);
My Makefile is
ifneq ($(KERNELRELEASE),)
include Kbuild
#KDIR ?= ../repos/linux
else
KDIR ?= /lib/modules/4.9.0-6-amd64/build
default:
$(MAKE) -C $(KDIR) M=$$PWD
clean:
$(MAKE) -C $(KDIR) M=$$PWD clean
endif
I start make as: make ARCH=arm CROSS_COMPILE='ccache arm-eabi-' PATH=/opt/gcc-linaro-7.2.1-2017.11-x86_64_arm-eabi/bin:$PATH
I compile on Debian 4.9.0-6-amd64. Target is arm32 4.16.18.
The problem is that I get a module for my host machine (I can insmod it), but the target kernel rejects it as invalid module.
When I try to change the linux path in the Makefile to the target kernel sources, the compilation fails with fatal error: asm/barrier.h: No such file or directory.
Related
I am newbee to linux kernel. Currently I want to have 2 module they can interact with each other. I've tried to call function2 from module2 in module1 by EXPORT_SYMBOL_GPL. When I 'insmod' module1 it tells me function2 is "unknown symbol" to module1. I did export function2 and add -DEXPORT_SYMTAB in Makefile. What else I miss? Any advice great appreciate.
Here's my hello samples
/* *************************************************************************************
* hello-1.c - The simplest kernel module.
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
#include "hello2.h"
static int __init init_module1(void)
{
printk(KERN_INFO "Hello world 1.\n");
function2();
/*
* A non 0 return means init_module failed; module can't be loaded.
*/
return 0;
}
static void __exit cleanup_module1(void)
{
printk(KERN_INFO "Goodbye world 1.\n");
}
module_init(init_module1);
module_exit(cleanup_module1);
MODULE_DESCRIPTION("Hello1");
MODULE_LICENSE("GPL");
/* *************************************************************************************
* hello-2.c - The simplest kernel module.
*/
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
static void function2 (void)
{
printk(KERN_INFO "Function called in hello2.\n");
}
EXPORT_SYMBOL_GPL(function2);
static int __init init_module2(void)
{
printk(KERN_INFO "Hello world 2.\n");
/*
* A non 0 return means init_module failed; module can't be loaded.
*/
return 0;
}
static void __exit cleanup_module2(void)
{
printk(KERN_INFO "Goodbye world 2.\n");
}
module_init(init_module2);
module_exit(cleanup_module2);
MODULE_DESCRIPTION("Hello2");
MODULE_LICENSE("GPL");
/* *************************************************************************************
* hello-2.h - The simplest kernel module header
*/
extern void function2 (void);
################################################
# Makefile for hello2
PWD := $(shell pwd)
KVERSION := $(shell uname -r)
KDIR := /lib/modules/$(shell uname -r)/build
KERNEL_DIR := /usr/src/linux-headers-$(KVERSION)/
INSTALL_PATH := /lib/modules/$(shell uname -r)/extra
EXTRA_CFLAGS = -DEXPORT_SYMTAB
MODULE_NAME = hello2
obj-m := hello2.o
#.PHONY: all clean insert
.PHONY: all clean
all:
$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:
$(MAKE) -C $(KDIR) M=$(PWD) clean
rm -rf *.o *.ko *.mod.* .c* .t*
insert:
$(MAKE) INSTALL_MOD_DIR=$(INSTALL_PATH) -C $(KDIR) M=$(PWD) modules_install
In hello-2.c you have:
static void function2 (void)
{
...
}
Please consider making it non-static:
void function2(void)
{
...
}
I found the solution from an old post:
insmod fails with "Unknown symbol in module" for a symbol defined in another module
Turns out 2 modules need to be built at the same time. I built they separately with 2 different Makefile.
I am trying to pass a "define variable called DEBUG" at compile time for a kernel module.
i.e provide the same functionality as DEBUG does below, but in a Makefile for a kernel module.
gcc -o foo -DDEBUG=1 foo.c
Can anyone give me a hint on how this can be achieved?
The Makefile:
# name of the module to be built
TARGET ?= test_module
# How to pass this during compile time? (-D$(DEBUG) or something similar)
DEBUG ?= 1
#define sources
SRCS := src/hello.c
#extract required object files
OBJ_SRCS := $(SRCS:.c=.o)
#define path to include directory containing header files
INCLUDE_DIRS = -I$(src)/includes
ccflags-y := $(INCLUDE_DIRS)
#define the name of the module and the source files
obj-m += $(TARGET).o
$(TARGET)-y := $(OBJ_SRCS)
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
#echo "insert module:\n\t sudo insmod $(TARGET).ko"
#echo "remove module:\n\t sudo rmmod $(TARGET)"
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
I am using the module from link (with a small change in the init function, see the #if #endif statement)
hello.c:
#include <linux/module.h> // included for all kernel modules
#include <linux/kernel.h> // included for KERN_INFO
#include <linux/init.h> // included for __init and __exit macros
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Lakshmanan");
MODULE_DESCRIPTION("A Simple Hello World module");
static int __init hello_init(void)
{
#if (DEBUG == 1)
printk(KERN_INFO "DEBUG = 1\n")
#endif
printk(KERN_INFO "Hello world!\n");
return 0; // Non-zero return means that the module couldn't be loaded.
}
static void __exit hello_cleanup(void)
{
printk(KERN_INFO "Cleaning up module.\n");
}
module_init(hello_init);
module_exit(hello_cleanup);
I would like to see that dmesg poduces the following after
sudo insmod test_module.ko
DEBUG = 1
Hello world!
Solution:
ccflags-y := -DDEBUG=$(DEBUG)
Made the code below execute as intended
#if (DEBUG == 1)
printk(KERN_INFO "DEBUG = 1\n")
#endif
ccflags-y := -DDEBUG=$(DEBUG)
Made the code below execute as intended
#if (DEBUG == 1)
printk(KERN_INFO "DEBUG = 1\n")
#endif
I have compiled this code:
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/genhd.h> // declaration of printk_all_partitions()
MODULE_LICENSE("GPL");
int __init start (void) {
printk ("evaluating the module ") ;
printk_all_partitions();
printk (" module inserted .. ");
return 0 ;
}
void __exit x(void) {
printk ("module unloaded ..");
}
module_init(start);
module_exit (x);
MODULE_LICENSE("GPL");
makefile is:
EXTRA_CFLAGS += -Wall
obj-m += printk_all_partitions.o
all :
make -C /lib/modules/$(shell uname -r )/build M=$(PWD) modules
clean :
make -C /lib/modules/$(shell uname -r )/build M=$(PWD) clean
when I run make I get
WARNING: "printk_all_partitions" [/root/c++/modulez/multiple_source_files/printk_plm/printk_all_partitions.ko] undefined!
egrep -w 'printk|printk_all_partitions' /proc/kallsyms :
ffffffff8162f135 T printk
ffffffff81ac7b46 T printk_all_partitions
Now the only difference between printk and printk_all_partitions is that printk_all_partitions does not exist in the Module.symvers
and printk is:
0x27e1a049 printk vmlinux EXPORT_SYMBOL
By the time i finished the writing I found out that a function must be EXPORT_SYMBOL-ed too in order for it to work
but if (somehow) Modules.symvers was deleted , and the kernel sources were not available, both printk and printk_all_partitions are begin with a "T", what other way to know is one is exported or not?
Normally this line
obj-m += printk_all_partitions.o
is the name of the module you're trying to create. In this case you're naming your module the same as an existing symbol, is this deliberate?
I'm a noob to linux kernel programming and thought I'd be able to find the answer for this (since it seems really simple) but haven't had any luck yet. I need to make a linux kernel module that prints the version number of the kernel. The assignment requires that implement a module which displays this kind of message when loaded:
"Hello Master. You are currently using Linux (version)", where (version) is the kernel version no.
How can I do this? I tried using uname (http://man7.org/linux/man-pages/man2/uname.2.html) but when I include sys/utsname.h, I get a fatal error upon compiling with my makefile
"Cannot open include file: 'sys/utsname.h': No such file or directory".
Here is my module
#undef __KERNEL__
#define __KERNEL__
#undef __MODULE__
#define __MODULE__
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <sys/utsname.h>
struct utsname unameData;
static int __init config_init(void)
{
uname(&unameData);
printk(KERN_INFO "Version number is %s\n", unameData.version);
return 0;
}
static void __exit config_exit(void)
{
printk(KERN_INFO "config_exit executed with success\n");
return;
}
module_init(config_init);
module_exit(config_exit);
MODULE_LICENSE("GPL");
Makefile
obj-m := config.o
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
all:
$(MAKE) -C $(KDIR) M=$(PWD) modules
clean:
$(MAKE) -C $(KDIR) M=$(PWD) clean
Firstly, you need to use the correct headers and also the correct function utsname(). Following code work well for me.
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/utsname.h>
static int __init my_init(void)
{
printk(KERN_INFO "Kernel version %s\n", utsname()->version);
printk(KERN_INFO "Kernel release %s\n", utsname()->release);
return 0;
}
static void __exit my_exit(void)
{
printk(KERN_INFO "exit module");
return;
}
module_init(my_init);
module_exit(my_exit);
MODULE_LICENSE("GPL");
dmesg output should looks something like this:
[ 1117.358451] Kernel version #64-Ubuntu SMP Mon Sep 22 21:28:38 UTC 2014
[ 1117.358457] Kernel release 3.13.0-37-generic
all:
I have 2 files, module1.c and module2.c which contains functions needed by the third file, big_module.c. My Makefile complained of not finding functions defined in module1.c and module2.c. These functions are needed by big_module.c Could you please help me defining my Makefile so it would work?
module1.c
#include <linux/module.h>
#include <linux/init.h>
#include <linux/version.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <asm/uaccess.h>
int module1 (struct file *filp, struct vm_area_struct *vma)
{ return 0; }
int __init init_module1 (void)
{ return 0; }
void __exit cleanup_module1 (void)
{ }
module2.c
#include <linux/module.h>
#include <linux/init.h>
#include <linux/version.h>
#include <linux/errno.h>
#include <asm/uaccess.h>
#include <asm/io.h>
unsigned long virt_addr;
int module2(struct file * filp, struct vm_area_struct * vma)
{ return 0; }
int __init init_module2 (void)
{ return 0; }
void __exit cleanup_module2 (void) { }
big_module.c
#include <linux/version.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/errno.h>
#include <linux/vt_kern.h>
#include <linux/fs.h>
MODULE_DESCRIPTION("Example");
MODULE_AUTHOR("Your Name Here");
MODULE_LICENSE("GPL");
static int __init hello_init(void)
{
init_module1();
init_module2();
return 0;
}
static void __exit hello_cleanup(void)
{
cleanup_module1();
cleanup_module2();
}
module_init(hello_init);
module_exit(hello_cleanup);
Makefile:
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
obj-m += big_module.o
obj-m += module1.o
obj-m += module2.o
modules:
$(MAKE) -C $(KDIR) M=$(PWD) modules
Errors:
> uu#uu-VirtualBox:~/UCSC-Ext/LDDII/Assignment3/ASK$ sudo make
> make -C /lib/modules/3.10.0uu/build M=/home/uu/UCSC-Ext/LDDII/Assignment3/ASK modules
> make[1]: Entering directory `/usr/src/linux-3.10'
> CC [M] /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.o
> /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.c: In function ‘hello_init’:
> /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.c:14:2: error: implicit declaration of function ‘init_module1’
> [-Werror=implicit-function-declaration]
> /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.c:15:2: error: implicit declaration of function ‘init_module2’
> [-Werror=implicit-function-declaration]
> /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.c: In function ‘hello_cleanup’:
> /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.c:21:2: error: implicit declaration of function ‘cleanup_module1’
> [-Werror=implicit-function-declaration]
> /home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.c:22:2: error: implicit declaration of function ‘cleanup_module2’
> [-Werror=implicit-function-declaration]
> cc1: some warnings being treated as errors
> make[2]: *** [/home/uu/UCSC-Ext/LDDII/Assignment3/ASK/big_module.o] Error 1
> make[1]: *** [_module_/home/uu/UCSC-Ext/LDDII/Assignment3/ASK] Error 2
> make[1]: Leaving directory `/usr/src/linux-3.10'
> make: *** [modules] Error 2
all:
I found the solution to my question. It's in the Makefile which should look
like the following:
Makefile
=======================
KDIR := /lib/modules/$(shell uname -r)/build
PWD := $(shell pwd)
obj-m := big_module.o
big_module-objs := module1.o module2.o
modules:
$(MAKE) -C $(KDIR) M=$(PWD) modules
=======================