Hi Russel, 2015-07-10 19:22 GMT+09:00 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>: > On Mon, Jul 06, 2015 at 09:37:04PM +0900, Masahiro Yamada wrote: >> [3] Then, re-build "all" and "uImage" simultaneously. >> You will get an invalid uImage at random. >> $ make -s -j8 ARCH=arm UIMAGE_LOADADDR=0x80208000 all uImage >> Image Name: Linux-4.2.0-rc1-00008-g1c4c715-d >> Created: Mon Jul 6 17:52:22 2015 >> Image Type: ARM Linux Kernel Image (uncompressed) >> Data Size: 26768 Bytes = 26.14 kB = 0.03 MB >> Load Address: 80208000 >> Entry Point: 80208000 > > At no point in the above do I see an attempt to rebuild init/main.o, > which there should be as you touched the corresponding .c file - > because you're hiding that output with -s. Please show what's going > on without using -s. Please see the log attached at the end of this message. >> "make uImage" could descend into arch/arm/boot/Makefile before >> "make zImage" is completed because arch/arm/Makefile describes no >> dependency among boot targets. > > The uImage target should depend on vmlinux, which should force the > rebuild of init/main.o, and relink of the top-level vmlinux file > before decending into arch/arm/boot/Makefile for the > arch/arm/boot/uImage target. > > That makefile contains the dependencies required to order things > correctly - the arch/arm/boot/uImage target depends on > arch/arm/boot/zImage, which in turn depends on > arch/arm/boot/compressed/vmlinux, and then arch/arm/boot/Image. > > In other words, arch/arm/boot/Makefile deals with the dependencies > between the targets it's responsible for building itself. No, you do not understand what is happening in here. The dependencies among targets such as Image, zImage, uImage, are fully described in arch/arm/boot/Makefile, but it is not enough. Because arch/arm/boot/Makefile is _not_ included from the top-level Makefile, the top-level build cannot know the dependency between zImage and uImage. arch/arm/Makefile, which is included from the top Makefile, only describes that zImage depends on vmlinux, and uImage depends on vmlinux as well. But, no dependency between zImage and uImage is written in arch/arm/Makefile. Consequently, we run make with the parallel option, first Kbuild updates vmlinux, and then two different threads descends into arch/arm/boot/Makefile almost at the same time, one for updating zImage and the other for uImage. The is a race between the two threads. While one thread is re-generating zImage and also uImage on top of that, the other thread tries to re-generate zImage independently. zImage is overwritten by the slower thread, and then uImage is re-generated based on the broken zImage. See my detailed build log below: Please note: "Kernel: arch/arm/boot/zImage is ready" is displayed twice, the first one is shown before the uImage log, and the second one is after uImage. zImage is correct, but uImage is extremely small when this problem happens. $ git describe v4.2-rc1-62-gc4b5fd3 $ touch init/main.c $ 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 GZIP arch/arm/boot/compressed/piggy.gzip 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-4.2.0-rc1-00062-gc4b5fd3-d Created: Sat Jul 11 01:22:22 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 $ LANG=C ls -l arch/arm/boot/ total 19636 -rwxrwxr-x 1 masahiro masahiro 13766656 Jul 11 01:22 Image -rw-rw-r-- 1 masahiro masahiro 3137 Jul 3 01:17 Makefile drwxrwxr-x 2 masahiro masahiro 4096 Jul 3 01:17 bootp drwxrwxr-x 2 masahiro masahiro 4096 Jul 11 01:22 compressed drwxrwxr-x 3 masahiro masahiro 155648 Jul 11 00:58 dts -rw-rw-r-- 1 masahiro masahiro 1648 Jul 3 01:17 install.sh -rw-rw-r-- 1 masahiro masahiro 26536 Jul 11 01:22 uImage -rwxrwxr-x 1 masahiro masahiro 6135048 Jul 11 01:22 zImage -- Best Regards Masahiro Yamada -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
