On Tue, Feb 19, 2019 at 01:42:13PM +0900, Masahiro Yamada wrote: [..]
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 set looks good to me and since the main use case is building bpf progs I can route it via bpf-next tree if there are no objections. Masahiro, could you please ack it?
Honestly, I was not tracking this thread since I did not know I was responsible for this.
I just started to take a closer look, then immediately got scared.
This version is not mature enough for the merge.
First of all, this patch cannot be compiled out-of-tree (O= option).
I do not know why 0-day bot did not catch this apparent breakage.
$ make -j8 O=hoge make[1]: Entering directory '/home/masahiro/workspace/bsp/linux/hoge' GEN Makefile Using .. as source for kernel DESCEND objtool CALL ../scripts/checksyscalls.sh CHK include/generated/compile.h make[2]: *** No rule to make target 'Module.symvers', needed by 'kernel/kheaders_data.txz'. Stop. make[2]: *** Waiting for unfinished jobs.... /home/masahiro/workspace/bsp/linux/Makefile:1043: recipe for target 'kernel' failed make[1]: *** [kernel] Error 2 make[1]: *** Waiting for unfinished jobs.... make[1]: Leaving directory '/home/masahiro/workspace/bsp/linux/hoge' Makefile:152: recipe for target 'sub-make' failed make: *** [sub-make] Error 2
I saw this build error for in-tree building as well.
We cannot build this from a pristine source tree.
For example, I observed the build error in the following procedure.
$ make mrproper $ make defconfig Set CONFIG_IKHEADERS_PROC=y $ make
Module.symvers is generated in the modpost stage (the very last stage of build).
But, vmlinux depends on kernel/kheaders_data.txz, which includes Module.symvers.
So, this is not so simple since it is a circular dependency...
I guess I was not building a pristine tree either and missed this circular dependency :-/ . Any ideas on how we can fix the Module.symvers issue? One idea is to reserve the space in the binaries, but only populate the space reserved in the binary *after* the modpost stage, once the archive is ready..
thanks,
- Joel