• Masahiro Yamada's avatar
    ARM: 8418/1: add boot image dependencies to not generate invalid images · 3939f334
    Masahiro Yamada authored
    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: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    3939f334
Makefile 12.6 KB