mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
synced 2026-01-26 19:51:35 +01:00
Build the Linux kernel independently from Buildroot
This will allow for other types of root filesystems that don't rely on Buildroot to be added and used in the future. Propagate --verbose on all build scripts to see full GCC commands. build-all: allow for neat subsets also 9p share rootfs_overlay. TODO document.
This commit is contained in:
Ciro Santilli 六四事件 法轮功
97
README.adoc
97
README.adoc
@@ -75,6 +75,8 @@ cd linux-kernel-module-cheat
|
||||
./configure --qemu && \
|
||||
./build-qemu &&
|
||||
./build-buildroot && \
|
||||
./build-linux && \
|
||||
./build-modules && \
|
||||
./run && \
|
||||
:;
|
||||
....
|
||||
@@ -98,7 +100,7 @@ see this: https://askubuntu.com/questions/496549/error-you-must-put-some-source-
|
||||
|
||||
It does not work if you just download the `.zip` from GitHub because we use link:.gitmodules[Git submodules], you must clone this repo. `./configure` then fetches only the required submodules for you.
|
||||
|
||||
QEMU opens up and you can start playing with the kernel modules inside the simulated system:
|
||||
QEMU opens up and you can start playing with the kernel modules inside the simulated system: TODO fix path to 9p:
|
||||
|
||||
....
|
||||
insmod /hello.ko
|
||||
@@ -210,10 +212,12 @@ pr_info("hello init hacked\n");
|
||||
and then rebuild the kernel modules and re-run to see it take effect:
|
||||
|
||||
....
|
||||
./build-buildroot --kernel-modules
|
||||
./build-modules
|
||||
./run --eval-busybox 'insmod /hello.ko'
|
||||
....
|
||||
|
||||
TODO mention 9p
|
||||
|
||||
Congratulations, you are now officially a kernel module hacker!
|
||||
|
||||
We use `./build-buildroot` because the kernel modules go inside the root filesystem, and it is Buildroot that generates and updates our root filesystem. The kernel modules are link:packages/kernel_modules[inside a Buildroot package].
|
||||
@@ -245,7 +249,7 @@ pr_info("I'VE HACKED THE LINUX KERNEL!!!");
|
||||
Then rebuild the Linux kernel and reboot:
|
||||
|
||||
....
|
||||
./build-buildroot && ./run
|
||||
./build-linux && ./run
|
||||
....
|
||||
|
||||
and, surely enough, your message has appeared at the beginning of the boot.
|
||||
@@ -321,6 +325,8 @@ All of this makes QEMU the natural choice of default system simulator.
|
||||
|
||||
=== gem5 Buildroot setup
|
||||
|
||||
TODO document kernel modules don't work on 9p
|
||||
|
||||
==== About the gem5 Buildroot setup
|
||||
|
||||
This setup is like the <<qemu-buildroot-setup>>, but it uses link:http://gem5.org/[gem5] instead of QEMU as a system simulator.
|
||||
@@ -535,7 +541,6 @@ The limitations are severe however:
|
||||
* can't <<gdb,GDB step debug the kernel>>, since the source and cross toolchain with GDB are not available. Buildroot cannot easily use a host toolchain: <<prebuilt-toolchain>>.
|
||||
+
|
||||
Maybe we could work around this by just downloading the kernel source somehow, and using a host prebuilt GDB, but we felt that it would be too messy and unreliable.
|
||||
* can't create new modules or modify the existing ones, since no cross toolchain
|
||||
* you won't get the latest version of this repository. Our <<travis>> attempt to automate builds failed, and storing a release for every commit would likely make GitHub mad at us.
|
||||
* <<gem5>> is not currently supported, although it should not be too hard to do. Annoyances:
|
||||
+
|
||||
@@ -583,6 +588,23 @@ then do whatever that checked out README says.
|
||||
|
||||
If you are curious to see what the releases contain in detail, have a look at our <<release,release procedure>>.
|
||||
|
||||
To build the kernel modules, simply do:
|
||||
|
||||
....
|
||||
./build-linux -- modules_prepare
|
||||
./build-modules
|
||||
./run
|
||||
....
|
||||
|
||||
`modules_prepare` does the minimal build procedure required on the kernel for us to be able to compile the kernel modules, and is way faster than doing a full kernel build. A full kernel build would also work however.
|
||||
|
||||
To modify the Linux kernel, build and use it as usual:
|
||||
|
||||
....
|
||||
./build-linux
|
||||
./run
|
||||
....
|
||||
|
||||
////
|
||||
For gem5, do:
|
||||
|
||||
@@ -601,11 +623,11 @@ The Linux kernel is required for `extract-vmlinux` to convert the compressed ker
|
||||
[[host]]
|
||||
=== Host kernel module setup
|
||||
|
||||
**THIS IS DANGEROUS, YOU HAVE BEEN WARNED**
|
||||
**THIS IS DANGEROUS (AND FUN), YOU HAVE BEEN WARNED**
|
||||
|
||||
This method runs the kernel modules directly on your host computer without a VM, and saves you the compilation time and disk usage of the virtual machine method.
|
||||
|
||||
It has however severe limitations, and you will soon see that the compilation time and disk usage are well worth it:
|
||||
It has however severe limitations:
|
||||
|
||||
* can't control which kernel version and build options to use. So some of the modules will likely not compile because of kernel API changes, since https://stackoverflow.com/questions/37098482/how-to-build-a-linux-kernel-module-so-that-it-is-compatible-with-all-kernel-rele/45429681#45429681[the Linux kernel does not have a stable kernel module API].
|
||||
* bugs can easily break you system. E.g.:
|
||||
@@ -618,20 +640,34 @@ It has however severe limitations, and you will soon see that the compilation ti
|
||||
Still interested?
|
||||
|
||||
....
|
||||
cd packages/kernel_modules
|
||||
./make-host.sh
|
||||
./build-modules --host
|
||||
....
|
||||
|
||||
If the compilation of any of the C files fails because of kernel or toolchain differences that we don't control on the host, just rename it to remove the `.c` extension and try again:
|
||||
Compilation will likely fail for some modules because of kernel or toolchain differences that we can't control on the host.
|
||||
|
||||
The best solution is to compile just your modules with:
|
||||
|
||||
....
|
||||
./build-modules --host -- hello hello2
|
||||
....
|
||||
|
||||
which is equivalent to:
|
||||
|
||||
....
|
||||
./build-modules --host -- packages/kernel/modules/hello.c packages/kernel/modules/hello2.c
|
||||
....
|
||||
|
||||
Or just remove the `.c` extension from the failing files and try again:
|
||||
|
||||
....
|
||||
cd "$(./getvar kernel_modules_src_dir)"
|
||||
mv broken.c broken.c~
|
||||
./build_host
|
||||
....
|
||||
|
||||
Once you manage to compile, and have come to terms with the fact that this may blow up your host, try it out with:
|
||||
|
||||
....
|
||||
cd "$(./getvar kernel_modules_build_host_dir)"
|
||||
sudo insmod hello.ko
|
||||
|
||||
# Our module is there.
|
||||
@@ -649,15 +685,6 @@ dmesg -T
|
||||
sudo lsmod | grep hello
|
||||
....
|
||||
|
||||
Once you are done with this method, you must clean up the in-tree build objects before you decide to do the right thing and move on to the superior `./build` Buildroot method:
|
||||
|
||||
....
|
||||
cd packages/kernel_modules
|
||||
./make-host.sh clean
|
||||
....
|
||||
|
||||
otherwise they will cause problems.
|
||||
|
||||
==== Hello host
|
||||
|
||||
Minimal host build system example:
|
||||
@@ -3362,6 +3389,8 @@ although this can be useful when someone gives you a random image.
|
||||
[[kernel-configs-about]]
|
||||
==== About our Linux kernel configs
|
||||
|
||||
TODO: explain link:update-buildroot-kernel-config[]
|
||||
|
||||
We have managed to come up with minimalistic kernel configs that work for both QEMU and gem5 (oh, the hours of bisection).
|
||||
|
||||
Our configs are all based on Buildroot's configs, which were designed for QEMU, and then on top of those we also add:
|
||||
@@ -7276,7 +7305,7 @@ Bibliography:
|
||||
|
||||
==== 9P gem5
|
||||
|
||||
Seems possible! Lets do it:
|
||||
TODO seems possible! Lets do it:
|
||||
|
||||
* http://gem5.org/wiki/images/b/b8/Summit2017_wa_devlib.pdf
|
||||
* http://gem5.org/WA-gem5
|
||||
@@ -10853,23 +10882,21 @@ We use it for:
|
||||
+
|
||||
C files for example need compilation, and must go through the regular package system, e.g. through link:packages/kernel_modules/user[].
|
||||
|
||||
=== CONTRIBUTING
|
||||
=== Test this repo
|
||||
|
||||
==== Testing
|
||||
This section describes how to run the most complete set of tests possible.
|
||||
|
||||
Testing that should be done for every functional patch.
|
||||
It takes too much time to be feasible for every patch, but it should be done for every release.
|
||||
|
||||
===== Guest testing
|
||||
|
||||
Run all tests:
|
||||
==== Automated tests
|
||||
|
||||
....
|
||||
./build-all
|
||||
./test
|
||||
./test --size 3
|
||||
echo $?
|
||||
....
|
||||
|
||||
Should output 0.
|
||||
should output 0.
|
||||
|
||||
Sources:
|
||||
|
||||
@@ -10893,7 +10920,7 @@ Test that the Internet works:
|
||||
|
||||
Source: link:rootfs_overlay/test_all.sh[].
|
||||
|
||||
===== Host testing
|
||||
===== Test GDB
|
||||
|
||||
Shell 1:
|
||||
|
||||
@@ -10914,7 +10941,7 @@ Then proceed to do the following tests:
|
||||
* `/count.sh` and `b __x64_sys_write`
|
||||
* `insmod /timer.ko` and `b lkmc_timer_callback`
|
||||
|
||||
==== Bisection
|
||||
=== Bisection
|
||||
|
||||
When updating the Linux kernel, QEMU and gem5, things sometimes break.
|
||||
|
||||
@@ -10953,7 +10980,7 @@ git submodule update
|
||||
|
||||
An example of Linux kernel commit bisection on gem5 boots can be found at: link:bisect-linux-boot-gem5[].
|
||||
|
||||
==== Update a forked submodule
|
||||
=== Update a forked submodule
|
||||
|
||||
This is a template update procedure for submodules for which we have some patches on on top of mainline.
|
||||
|
||||
@@ -10979,7 +11006,7 @@ git rebase --onto "$next_mainline_revision" "$last_mainline_revision"
|
||||
git commit -m "linux: update to ${next_mainline_revision}"
|
||||
....
|
||||
|
||||
==== Sanity checks
|
||||
=== Sanity checks
|
||||
|
||||
Basic C and C++ hello worlds:
|
||||
|
||||
@@ -11000,7 +11027,7 @@ Sources:
|
||||
* link:packages/kernel_modules/user/hello.c[]
|
||||
* link:packages/kernel_modules/user/hello_cpp.c[]
|
||||
|
||||
===== rand_check.out
|
||||
==== rand_check.out
|
||||
|
||||
Print out several parameters that normally change randomly from boot to boot:
|
||||
|
||||
@@ -11015,7 +11042,7 @@ This can be used to check the determinism of:
|
||||
* <<norandmaps>>
|
||||
* <<qemu-record-and-replay>>
|
||||
|
||||
==== Release
|
||||
=== Release
|
||||
|
||||
Create a release:
|
||||
|
||||
@@ -11042,7 +11069,7 @@ This should in particular enable to easily update <<prebuilt>>.
|
||||
|
||||
TODO also run tests and only release if they pass.
|
||||
|
||||
===== release-zip
|
||||
==== release-zip
|
||||
|
||||
Create a zip containing all files required for <<prebuilt>>
|
||||
|
||||
|
||||
Reference in New Issue
Block a user