[Buildroot] Re-building a Linux Net-bootable image after all other components are built

[Peter Seiderer]

Hello Stephen,

On Wed, 22 Jul 2020 18:05:39 -0400, Stephen Beckwith <embeddedsteve at gmail.com> wrote:

> Please pardon the verbosity of this - I am a believer that the more you
> know (i.e. context) the better.  I am grateful for your expertise and
> assistance.
> Regards,
> Stephen Beckwith
> 
> *In original setup:*
> 
> BR 2015.08.1  With GCC 4.4.7 (BR Build)
> 
> Kernel = linux-3.14.17-pilot4  {with patches}
> 
> U-Boot = u-boot-2013.07-pilot4  {with patches}
> 
>  - in this setup, everything works fine.  We complete our build steps, then
> we go back and do a “rebuild” of the Linux kernel as shown below.  The
> output uImage (renamed to uImage_netboot) will be approximately the same
> size as the output image we create for flashing:  ~ 26MB.
> 
>  - This will be a linux kernel (~ 2.8MB) + an INITRAMFS attached - to make
> the total size.
> 
> 
> *New Setup:*
> 
> BR 2020.02.1  With GCC 9.2.0 (and updated glibc as well)
> 
> Kernel and U-boot are the same, with some additional patches to allow for
> successful compile.
> 
>  - here, the final output is ~ the same as the previous build.
> 
>  - However, when we go to remake the Netboot image, we only get the Kernel
> output size of ~ 2.8MB, without the attached ROOT FILE SYSTEM.
> 
> 
> Investigation seems to show that the updated Buildroot internals are doing
> somethings differently vs. how we had implemented this in the current setup.
> The linux .config (in the output/build/linux-custom directory) seems to be
> getting overwritten by Buildroot AFTER we have manually modified it (shown
> below).  When I searched the .config file in the linux build directory, the
> parameters set below are NOT present, which leads me to believe that
> Buildroot is overwriting this during the reconfigure step (which it didn’t
> use to in the current setup).
> 
> 
> I’m looking for suggestions on how to do this post-processing build with
> the new Buildroot setup to generate this image.  We have the rootfs.cpio
> file to be attached to the kernel, just need to figure out how to do this
> “correctly”.
> 
> 
> *BR Configuration:*
> 
> BR2_ROOTFS_POST_IMAGE_SCRIPT="$(BR2_EXTERNAL_SP_DEV_PATH)/scripts/post_image_build.sh"
> 
> 
> The post_image_build.sh script calls: buildrootfs_binary_files script
> 
> This script will Generate the ext4 RFS images required (verified they are
> correct)
> 
> The post_image_build.sh then creates the package we flash on our devices,
> packing up the kernel and RFS with a “header” for our update process.
> 
> The very last step done in the entire process is to call:
> build_netbooting_image.sh
> 
> 
> This build_netbooting_image.sh script will:
> 
> Save off the uImage in the build directory, saves the original config file
> as well
> 
> It then “tweaks” the output/build/linux-custom directory’s .config file
> 
> CONFIG_INITRAMFS_SOURCE=${BR_BINARIES_DIR}/rootfs.cpio
> 
> CONFIG_INITRAMFS_ROOT_UID = 0
> 
> CONFIG_INITRAMFS_ROOT_GID =0
> 
> CONFIG_INITRAMFS_COMPRESSION_NONE = y
> 
> cd into the output directory and from here does a “make linux-reconfigure”

Would suspect this command, did not look at what the old buildroot version
is doing, but the actual one re-writes the linux-kernel .config file....

Try (after tweaking the .config file) with (as linux-menuconfig does):

	$ rm build/linux-custom/.stamp_built \
		build/linux-custom/.stamp_configured \
		build/linux-custom/.stamp_images_installed \
		build/linux-custom/.stamp_target_installed
	$ make

linux-reconfigure re-does although the stages '.stamp_dotconfig' and
'.stamp_kconfig_fixup_done'...

Regards,
Peter

> 
> Does clean up and re-copy of images: so we get a “uImage_netboot” of ~ 26MB
> 
> 
> This is the exact same process that we do with current buildroot setup -
> the only real difference is the Buildroot infrastructure and the compiler.
> 
> 
> *Current Build:*
> 
>   LD      vmlinux
> 
>   SORTEX  vmlinux
> 
>   SYSMAP  System.map
> 
>   OBJCOPY arch/arm/boot/Image
> 
>   Kernel: arch/arm/boot/Image is ready
> 
>   GZIP    arch/arm/boot/compressed/piggy.gzip
> 
>   AS      arch/arm/boot/compressed/piggy.gzip.o
> 
> arm-buildroot-linux-gnueabi-gcc: warning:
> /u/sbeckwit/p4/spNext/mendo_dev/src/include: linker input file unused
> because linking not done
> 
>   LD      arch/arm/boot/compressed/vmlinux
> 
>   OBJCOPY arch/arm/boot/zImage
> 
>   Kernel: arch/arm/boot/zImage is ready
> 
>   UIMAGE  arch/arm/boot/uImage
> 
> Image Name:   Linux-3.14.17-ami
> 
> Created:      Thu Jun 11 15:17:52 2020
> 
> Image Type:   ARM Linux Kernel Image (uncompressed)
> 
> *Data Size:    26622048 Bytes = 25998.09 kB = 25.39 MB*
> 
> Load Address: 81008000
> 
> Entry Point:  81008000
> 
>   Image arch/arm/boot/uImage is ready
> 
>   CHK     include/config/kernel.release
> 
>   CHK     include/generated/uapi/linux/version.h
> 
>   CHK     include/generated/utsrelease.h
> 
> make[6]: `include/generated/mach-types.h' is up to date.
> 
>   CALL    scripts/checksyscalls.sh
> 
> arm-buildroot-linux-gnueabi-gcc: warning:
> /u/sbeckwit/p4/spNext/mendo_dev/src/include: linker input file unused
> because linking not done
> 
>   Building modules, stage 2.
> 
>   MODPOST 8 modules
> 
> 
> *New Build:*
> 
>   CHK     include/config/kernel.release
> 
>   CHK     include/generated/uapi/linux/version.h
> 
>   CHK     include/generated/utsrelease.h
> 
> make[6]: 'include/generated/mach-types.h' is up to date.
> 
>   CALL    scripts/checksyscalls.sh
> 
> arm-buildroot-linux-gnueabi-gcc.br_real: warning:
> /home/sbeckwit/sp_dev/bowie_dev/src/include: linker input file unused
> because linking not done
> 
>   CHK     include/generated/compile.h
> 
>   CHK     kernel/config_data.h
> 
>   Kernel: arch/arm/boot/Image is ready
> 
>   Kernel: arch/arm/boot/zImage is ready
> 
>   UIMAGE  arch/arm/boot/uImage
> 
> Image Name:   Linux-3.14.17-ami
> 
> Created:      Thu Jun 11 15:04:23 2020
> 
> Image Type:   ARM Linux Kernel Image (uncompressed)
> 
> *Data Size:    2824656 Bytes = 2758.45 KiB = 2.69 MiB*
> 
> Load Address: 81008000
> 
> Entry Point:  81008000
> 
>   Image arch/arm/boot/uImage is ready
> 
>  - More detailed listings can be provided.