How to rebuild kernel only?

[ma...@xemi.net]

Is there a command to rebuild kernel only?

Typically usually something like "make -j8 kernel" would work... but doesn't seem to rebuild kernel after making changes.

I suppose I could remove the kernel obj directory, but that would rebuild the entire kernel, not just the changes.

[Chih-Wei Huang]

The reason is the Androud build system won't parse
kernel's makefile directly so it won't see the changes
in the kernel tree.

To force to rebuild kernel, you can touch the kernel
config file (kernel/arch/x86/configs/android-x86_*)
or just remove the kernel image:

rm $OUT/kernel

Either way will trigger kernel rebuilding.

--
Chih-Wei
Android-x86 project
http://www.android-x86.org

[Mauro Rossi]

Hi Chih-Wei,

just a question, when I perform changes in kernel in order to force rebuild of kernel,

I tried to delete the .config file in out/target/product/{x86,x86_64}/obj/kernel

in this case kernel is also rebuilt, 

but I wanted to check is this way or other ways limiting the re-build only to changed parts in the sources,

or there some drawback (e.g. entire kernel is rebuilt) in some of these ways or all of them?

Thanks for comments

Mauro

[Chih-Wei Huang]

2018-07-19 12:46 GMT+08:00 Mauro Rossi <issor...@gmail.com>:
> Hi Chih-Wei,
> just a question, when I perform changes in kernel in order to force rebuild
> of kernel,
> I tried to delete the .config file in
> out/target/product/{x86,x86_64}/obj/kernel
> in this case kernel is also rebuilt,

Surely it's OK to do so.

> but I wanted to check is this way or other ways limiting the re-build only
> to changed parts in the sources,
> or there some drawback (e.g. entire kernel is rebuilt) in some of these ways
> or all of them?

As I've said, the reason is the Android build system doesn't parse
kernel's makefile (kbuild). That means the kernel tree is not on the
dependency path to build an Android image.
The current only dependency I set is

system.sfs -> $OUT/kernel -> $OUT/obj/kernel/.config ->
kernel/arch/x86/configs/android-x86_*

So if you want to rebuild kernel, you just need to change (touch)
any file on the the dependency path.

Basically speaking, Android build system is totally different
than kbuild. kbuild is a traditionally recursive make system,
(i.e., subfolders are made by submake)
while Android's is designed to be non-recursive.
It's very hard to integrate them together seamless.

Since Android build system is using ninja now,
I'm also looking at the Kninja project:

https://github.com/rabinv/kninja

It may give us an opportunity to integrate the two
build systems seamless.
But it's just a low priority task. I haven't try it yet.

[youling 257]

when you change kernel source tree，you need delete output kernel and modules，then under Android source tree，lunch command rebuild iso，

write iso to u-disk，run live mode on your test device .

you do that ?

在 2018年7月19日星期四 UTC+8下午12:46:56，Mauro Rossi写道：

[youling 257]

git clone kernel source，cd kernel source folder

make android-x86_64_defconfig -C . O=../64

cd ../64

time make targz-pkg -j8

在 2018年7月19日星期四 UTC+8上午10:20:22，ma...@xemi.net写道：

[youling 257]

$ cd 3

$ git am 0001-platform-x86-touchscreen_dmi-Add-info-for-the-Cube-K.patch

fatal: could not open '0001-platform-x86-touchscreen_dmi-Add-info-for-the-Cube-K.patch' for reading: No such file or directory

$ git am ../0001-platform-x86-touchscreen_dmi-Add-info-for-the-Cube-K.patch

Applying: platform/x86: touchscreen_dmi: Add info for the Cube KNote i1101 tablet

$

root@localhost:/home/youling257# cd /data/data/com.termux/files/home/64

root@localhost:/data/data/com.termux/files/home/64# time make targz-pkg -i -j8

make KBUILD_SRC=

  GEN ./Makefile

  DESCEND objtool

  Using /data/data/com.termux/files/home/3 as source for kernel

  CALL /data/data/com.termux/files/home/3/scripts/checksyscalls.sh

  CHK include/generated/compile.h

  CC drivers/platform/x86/touchscreen_dmi.o

  AR drivers/platform/x86/built-in.a

  AR drivers/platform/built-in.a

  AR drivers/built-in.a

  GEN .version

  CHK include/generated/compile.h

  UPD include/generated/compile.h

  CC init/version.o

  AR init/built-in.a

  AR built-in.a

  LD vmlinux.o

  MODPOST vmlinux.o

  KSYM .tmp_kallsyms1.o

  KSYM .tmp_kallsyms2.o

  LD vmlinux

  SORTEX vmlinux

  SYSMAP System.map

  Building modules, stage 2.

  CC arch/x86/boot/version.o

  AS arch/x86/boot/compressed/head_64.o

  VOFFSET arch/x86/boot/compressed/../voffset.h

  OBJCOPY arch/x86/boot/compressed/vmlinux.bin

  RELOCS arch/x86/boot/compressed/vmlinux.relocs

  CC arch/x86/boot/compressed/kaslr.o

  CC arch/x86/boot/compressed/pgtable_64.o

  GZIP arch/x86/boot/compressed/vmlinux.bin.gz

  CC arch/x86/boot/compressed/misc.o

  MKPIGGY arch/x86/boot/compressed/piggy.S

  AS arch/x86/boot/compressed/piggy.o

  DATAREL arch/x86/boot/compressed/vmlinux

  LD arch/x86/boot/compressed/vmlinux

  ZOFFSET arch/x86/boot/zoffset.h

  OBJCOPY arch/x86/boot/vmlinux.bin

  AS arch/x86/boot/header.o

  LD arch/x86/boot/setup.elf

  OBJCOPY arch/x86/boot/setup.bin

  BUILD arch/x86/boot/bzImage

Setup is 16156 bytes (padded to 16384 bytes).

System is 8657 kB

CRC 146a8cd6

Kernel: arch/x86/boot/bzImage is ready (#3)