On Mon, Feb 11, 2019 at 10:39:43AM +0900, Masahiro Yamada wrote:
On Fri, Feb 8, 2019 at 6:13 AM Joel Fernandes (Google) joel@joelfernandes.org wrote:
Introduce in-kernel headers and other artifacts which are made available as an archive through proc (/proc/kheaders.txz file). This archive makes it possible to build kernel modules, run eBPF programs, and other tracing programs that need to extend the kernel for tracing purposes without any dependency on the file system having headers and build artifacts.
On Android and embedded systems, it is common to switch kernels but not have kernel headers available on the file system. Raw kernel headers also cannot be copied into the filesystem like they can be on other distros, due to licensing and other issues. There's no linux-headers package on Android. Further once a different kernel is booted, any headers stored on the file system will no longer be useful. By storing the headers as a compressed archive within the kernel, we can avoid these issues that have been a hindrance for a long time.
The feature is also buildable as a module just in case the user desires it not being part of the kernel image. This makes it possible to load and unload the headers on demand. A tracing program, or a kernel module builder can load the module, do its operations, and then unload the module to save kernel memory. The total memory needed is 3.8MB.
The code to read the headers is based on /proc/config.gz code and uses the same technique to embed the headers.
To build a module, the below steps have been tested on an x86 machine: modprobe kheaders rm -rf $HOME/headers mkdir -p $HOME/headers tar -xvf /proc/kheaders.txz -C $HOME/headers >/dev/null cd my-kernel-module make -C $HOME/headers M=$(pwd) modules rmmod kheaders
Signed-off-by: Joel Fernandes (Google) joel@joelfernandes.org
Changes since RFC: Both changes bring size down to 3.8MB:
- use xz for compression
- strip comments except SPDX lines
- Call out the module name in Kconfig
- Also added selftests in second patch to ensure headers are always
working.
Documentation/dontdiff | 1 + arch/x86/Makefile | 2 ++ init/Kconfig | 11 ++++++ kernel/.gitignore | 2 ++ kernel/Makefile | 29 +++++++++++++++ kernel/kheaders.c | 74 +++++++++++++++++++++++++++++++++++++++ scripts/gen_ikh_data.sh | 19 ++++++++++ scripts/strip-comments.pl | 8 +++++ 8 files changed, 146 insertions(+) create mode 100644 kernel/kheaders.c create mode 100755 scripts/gen_ikh_data.sh create mode 100755 scripts/strip-comments.pl
diff --git a/Documentation/dontdiff b/Documentation/dontdiff index 2228fcc8e29f..05a2319ee2a2 100644 --- a/Documentation/dontdiff +++ b/Documentation/dontdiff @@ -151,6 +151,7 @@ int8.c kallsyms kconfig keywords.c +kheaders_data.h* ksym.c* ksym.h* kxgettext diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 88398fdf8129..ad176d669da4 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -240,6 +240,8 @@ archmacros: ASM_MACRO_FLAGS = -Wa,arch/x86/kernel/macros.s export ASM_MACRO_FLAGS KBUILD_CFLAGS += $(ASM_MACRO_FLAGS) +IKH_EXTRA += arch/x86/kernel/macros.s +export IKH_EXTRA
This does not exist in any of released kernels.
See commit 6ac389346e6
Ok, thanks fixed it in v2 which I just sent and rebased on linus master branch.
- Joel