ARM: 8418/1: add boot image dependencies to not generate invalid images
U-Boot is often used to boot the kernel on ARM boards, but uImage
is not built by "make all", so we are often inclined to do
"make all uImage" to generate DTBs, modules and uImage in a single
command, but we should notice a pitfall behind it. In fact,
"make all uImage" could generate an invalid uImage if it is run with
the parallel option (-j).
You can reproduce this problem with the following procedure:
[1] First, build "all" and "uImage" separately.
You will get a valid uImage
$ git clean -f -x -d
$ export CROSS_COMPILE=<your-tools-prefix>
$ make -s -j8 ARCH=arm multi_v7_defconfig
$ make -s -j8 ARCH=arm all
$ make -j8 ARCH=arm UIMAGE_LOADADDR=0x80208000 uImage
CHK include/config/kernel.release
CHK include/generated/uapi/linux/version.h
CHK include/generated/utsrelease.h
make[1]: `include/generated/mach-types.h' is up to date.
CHK include/generated/timeconst.h
CHK include/generated/bounds.h
CHK include/generated/asm-offsets.h
CALL scripts/checksyscalls.sh
CHK include/generated/compile.h
Kernel: arch/arm/boot/Image is ready
Kernel: arch/arm/boot/zImage is ready
UIMAGE arch/arm/boot/uImage
Image Name: Linux-4.2.0-rc5-00156-gdd2384a7-d
Created: Sat Aug 8 23:21:35 2015
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 6138648 Bytes = 5994.77 kB = 5.85 MB
Load Address: 80208000
Entry Point: 80208000
Image arch/arm/boot/uImage is ready
$ ls -l arch/arm/boot/*Image
-rwxrwxr-x 1 masahiro masahiro 13766656 Aug 8 23:20 arch/arm/boot/Image
-rw-rw-r-- 1 masahiro masahiro 6138712 Aug 8 23:21 arch/arm/boot/uImage
-rwxrwxr-x 1 masahiro masahiro 6138648 Aug 8 23:20 arch/arm/boot/zImage
[2] Update some source file(s)
$ touch init/main.c
[3] Then, re-build "all" and "uImage" simultaneously.
You will get an invalid uImage at random.
$ make -j8 ARCH=arm UIMAGE_LOADADDR=0x80208000 all uImage
CHK include/config/kernel.release
CHK include/generated/uapi/linux/version.h
CHK include/generated/utsrelease.h
make[1]: `include/generated/mach-types.h' is up to date.
CHK include/generated/timeconst.h
CHK include/generated/bounds.h
CHK include/generated/asm-offsets.h
CALL scripts/checksyscalls.sh
CC init/main.o
CHK include/generated/compile.h
LD init/built-in.o
LINK vmlinux
LD vmlinux.o
MODPOST vmlinux.o
GEN .version
CHK include/generated/compile.h
UPD include/generated/compile.h
CC init/version.o
LD init/built-in.o
KSYM .tmp_kallsyms1.o
KSYM .tmp_kallsyms2.o
LD vmlinux
SORTEX vmlinux
SYSMAP System.map
OBJCOPY arch/arm/boot/Image
Building modules, stage 2.
Kernel: arch/arm/boot/Image is ready
GZIP arch/arm/boot/compressed/piggy.gzip
AS arch/arm/boot/compressed/piggy.gzip.o
Kernel: arch/arm/boot/Image is ready
LD arch/arm/boot/compressed/vmlinux
GZIP arch/arm/boot/compressed/piggy.gzip
OBJCOPY arch/arm/boot/zImage
Kernel: arch/arm/boot/zImage is ready
UIMAGE arch/arm/boot/uImage
Image Name: Linux-4.2.0-rc5-00156-gdd2384a7-d
Created: Sat Aug 8 23:23:14 2015
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 26472 Bytes = 25.85 kB = 0.03 MB
Load Address: 80208000
Entry Point: 80208000
Image arch/arm/boot/uImage is ready
MODPOST 192 modules
AS arch/arm/boot/compressed/piggy.gzip.o
LD arch/arm/boot/compressed/vmlinux
OBJCOPY arch/arm/boot/zImage
Kernel: arch/arm/boot/zImage is ready
$ ls -l arch/arm/boot/*Image
-rwxrwxr-x 1 masahiro masahiro 13766656 Aug 8 23:23 arch/arm/boot/Image
-rw-rw-r-- 1 masahiro masahiro 26536 Aug 8 23:23 arch/arm/boot/uImage
-rwxrwxr-x 1 masahiro masahiro 6138648 Aug 8 23:23 arch/arm/boot/zImage
Please notice the uImage is extremely small when this issue is
encountered. Besides, "Kernel: arch/arm/boot/zImage is ready" is
displayed twice, before and after the uImage log.
The root cause of this is the race condition between zImage and
uImage. Actually, uImage depends on zImage, but the dependency
between the two is only described in arch/arm/boot/Makefile.
Because arch/arm/boot/Makefile is not included from the top-level
Makefile, it cannot know the dependency between zImage and uImage.
Consequently, when we run make with the parallel option, Kbuild
updates vmlinux first, and then two different threads descends into
the arch/arm/boot/Makefile almost at the same time, one for updating
zImage and the other for uImage. While one thread is re-generating
zImage, the other also tries to update zImage before creating uImage
on top of that. zImage is overwritten by the slower thread and then
uImage is created based on the half-written zImage.
This is the reason why "Kernel: arch/arm/boot/zImage is ready" is
displayed twice, and a broken uImage is created.
The same problem could happen on bootpImage.
This commit adds dependencies among Image, zImage, uImage, and
bootpImage to arch/arm/Makefile, which is included from the
top-level Makefile.
Signed-off-by: 
Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: 
Russell King <rmk+kernel@arm.linux.org.uk>
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