When building a Kernel Driver out of tree,
i run make like this in the drivers directory, where KERNELDIR either is the path to the kernel source, or to the headers.
make -C $(KERNELDIR) M=$(PWD) modules
when trying to build headers myself using:
make headers_install ARCH=i386 INSTALL_HDR_PATH=$(HEADERSDIR)
i find the export unsuitable to build modules against (without a full kernel source tree)
Several files and folders seem to be missing, like a Makefile, scripts , include/generated/autoconf.h or include/config/auto.conf etc.
Debian does things in an usable way, as described in rules.real, although it does more than is described in Documentation/make/headers_install.txt , which seems to be not the "standard" way.
In short: how do i correctly export linux headers, so i can build external modules against it?
headers_install is meant to export a set of header files suitable to use from a user space point of view. It is the userspace exposed API of the kernel. Let's say you create a wonderful new ioctl, with a custome data structure. This is the kind of information you wan't userspace to know, so that userspace program can use your wonderful new ioctl.
But everything that is not visible from userspace, that is "private" to the kernel, or in other word the internal API, is not exposed to userspace.
So to build an out of tree module, you need either a full configured source tree, or the kernel headers as packaged by your distro. Look for the linux-headers or linux-kernel-headers
package on a Ubuntu / Debian for example.
I believe the kernel make file target of headers_install is meant for the production of Linux header for the production of C library and tool chain and not for the purpose of enabling to build out of tree kernel modules sans full configured kernel source code.
In fact, I'm guessing building out of tree kernel modules without full kernel source code is not supported and is in fact a "hack" created by distributions.
Related
I'm trying to add a system call to my OS and when I read the online tutorials, it always starts with downloading and extracting a kernel source code from the Internet. For example:
$ wget https://cdn.kernel.org/pub/linux/kernel/v4.x/linux-4.4.56.tar.xz to download the .tar.xz file.
And $ tar -xvJf linux-4.4.56.tar.xz to extract the kernel source code.
My question is: why do we have to use another kernel source from the Internet? Can we add the new system call to the running OS and compile it directly?
I'm trying to add a system call to my OS and when I read the online tutorials, it always starts with downloading and extracting a kernel source code from the Internet.
Well, that's right. You need to modify the kernel source code in order to implement a new syscall.
why do we have to use another kernel source from the Internet?
It's not "another kernel source", it's just "a kernel source". You don't usually have the source code for your currently installed kernel already at hand.
Normally, most Linux distributions provide a binary package for the kernel itself (which is automatically installed), a package for its headers only (which can be used to compile new modules), and possibly a source package related the binary package.
For example, on Ubuntu or Debian (assuming that you have enabled source packages) you should be able to get the current kernel source:
apt-get source linux-image-$(uname -r)
Since the tutorial author cannot possibly know which kernel version or which Linux distribution you are using, or even if your distribution provides a kernel source package at all, they just tell you to download a kernel source package from that Linux kernel website. This also ensures you use the exact same version that is shown in the tutorial, to avoid any compatibility problem with newer/older kernel versions.
Furthermore, you usually don't want to play around with the kernel of the machine you are using, since if something bad happens, you can end up damaging your system. You usually want to use a virtual machine for experimenting.
Can we add the new system call to the running OS and compile it directly?
Not really, it's not possible to hot-patch a new syscall into a running kernel. Since you need to modify the source code, first of all you need to have the source. Secondly, you'll need to do whatever modification you need and then compile the new kernel. Thirdly, you'll need to properly install the new kernel and reboot the machine.
I have a question regarding best practices for Yocto Project.
What i want to do is to add sources for a driver from github in kernel and rebuild the whole yocto image, but i am not sure what's the best way of doing that. I am thinking of two options possible here.
Fork the kernel sources into my own repo, then add the driver sources, update the Makefile and Kconfig and provide my own defconfig file. (this definitely works)
The second thing that crosses my mind is to use the initial kernel sources and just create a recipe that fetches the driver code into place (drivers/net/...) and create a patch that adds the driver to the Makefile and Kconfig and replaces the defconfig file and then rebuild. (I am not sure about this, if it is possible to fetch a driver sources into a specific place in the kernel sources)
So my question is if the second way would be possible and it's common to have it this way.
But if i am thinking again maybe that is not possible because i have the recipe for the kernel which fetches the kernel sources then compile them, so i think that it may not be possible to have a kernel recipe that fetches the kernel sources then another recipe that fetches the driver sources, applies the patch and only after this the kernel is compiled. Am i right? or this should be possible somehow?
Thanks.
I know how to make loadable kernel modules in Linux.
But i want that loadable kernel module to be a part of the kernel , and after booting that driver should automatically load, like most of the other general driver.
How to do that?
There are two ways to do for your query
1) building your module as statically compiled along with kernel(your source code should reside in kernel tree ),so while building build it static which come as a part of kernel,
so when kernel boots your module will be loaded.
2)Same as above but while building build as dynamic loadable module so that wheneever required you can load it.
to illustrate above concept you can try below link for simple helloworld example.
http://www.agusbj.staff.ugm.ac.id/abjfile/Chap8.pdf
You have to configure modprobe to load automatically driver after kernel boot. Here an example of configuration.
If you want to a built-in module, you must re-compile the kernel, and set Y in the configuration file on all modules that you want inside the kernel
I want to compile and later modify a Linux kernel code but I cannot do it by installing and running separate Linux system like Ubuntu and then compiling this kernel on linux system as I am not able to work on full fledged Linux system(Laptop hardware problems).I want to do it on Windows 7.Is there a way that I can do it?
The Linux kernel source tree has different files in some directories whose names only differ in capitalization, so unpacking the source tree would have to happen in a directory where the POSIX compatibility mode was active. Furthermore, you need a cross compiler targetting Linux, and an appropriate shell environment.
It can be done within the Cygwin environment if so desired, but I suspect it is significantly easier to run a Linux virtual machine, or CoLinux.
i Think you are talking about this have a look on this site they provide a way to compile and modify and infact build a new kernel in Visual Studio hope it will help you
I am very newbie in this kind of business. I have just cross compiled Linux kernel. But I have few question to ask which I have to know.
When we compile a Linux kernel I am using this piece of command, because my target platform is ARM.
make ARCH=arm CROSS_COMPILE=arm-none-linux-gnueabi-
Could I cross compile any Open Source software like that or Is it depends on the software release that the software supports cross compilation or not?
The Linux kernel source contains a arch folder for separate architectures but gcc, gLibc, binutils doesn't have, why?
But those can be cross-compiled. Can any one tell me why this kind of behavior happens?
Is there any standard way to cross-compile different kind of software as per requirement?? Please lead me if any one proficient in this kind of business.
Thank you.
There is a general way for cross compilation of software in linux if that is having configure
script.
Extract the source code of the package that you want to install .
See whether that has any configure script in it.
If that is , then run
./configure --help
to find the options supported for compilation .
I usually use the following command to cross compile.
./configure --host=arm-none-linux-eabi --prefix=/path/to/where/you/want/to/install
Based on the package may be required to give additional options.
Examples like --with-out= libtiff etc.
If that is not having any configure script then tweak into the make file.
The linux kernel has its own, very particular, build-system that is set up - not only for cross-compilation - but multiple architecture cross-compilation. This is why a series of arch folders exists.
A large amount (but by no means all) of open-source user-space software uses GNU autoconf to manage the configuration and build process. The purpose of autoconf is somewhat different from the kernel build script - it allows software to be built on a wide variety of subtly different UNIX-like build hosts for a equally wide variety of build targets.
autoconf can be used used for cross-compilation with a bit of work. There are some hints here. In principle, the build process needs to know:
Which set of tools to use (e.g. gcc, binutils)
Where the target's headers and libraries are staged
Where to install the resulting product.
gcc and binutils are slightly special case in that cross-tools are installed on a development host alongside the host's own tools. Since build processes might well use both, it's untenable that selection of tools is done entirely by the executable search path. Instead, cross-tools are named with a target-specific name format - e.g.
arm-linux-gnueabi-gcc
and
i686-apple-darwin11-llvm-gcc