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Date: Wed, 26 Nov 2014 14:57:42 +0100 From: Linus Walleij <linus.walleij@...aro.org> To: Jason Cooper <jason@...edaemon.net> Cc: Russell King - ARM Linux <linux@....linux.org.uk>, Michal Marek <mmarek@...e.cz>, Grant Likely <grant.likely@...retlab.ca>, Rob Herring <rob.herring@...aro.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: [PATCH] ARM: kbuild: Fix forced rebuild after 'make dtbs' On Wed, Nov 26, 2014 at 1:57 AM, Jason Cooper <jason@...edaemon.net> wrote: > On Tue, Nov 25, 2014 at 11:51:50PM +0000, Russell King - ARM Linux wrote: >> I think this needs a bit more debugging to see why the whole kernel is >> being rebuilt - the kernel build system has methods to tell you why stuff >> is being built, which would be a good place to start. > > Linus, since you were the one experiencing the regression, care to take > a whack at that? OK this full example should be possible to repeat for anyone with a cross compiler, and uses a separate build dir, and yeah there was something fishy: the bug only appears if you specify CONFIG_DEBUG_SECTION_MISMATCH=y: make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 u300_defconfig make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage -> no rebuild, just relink make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 u300_defconfig make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage CONFIG_DEBUG_SECTION_MISMATCH=y make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage CONFIG_DEBUG_SECTION_MISMATCH=y -> no rebuild, just relink make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 u300_defconfig make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 dtbs make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage -> no rebuild, just relink make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 u300_defconfig make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage CONFIG_DEBUG_SECTION_MISMATCH=y make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 dtbs make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage CONFIG_DEBUG_SECTION_MISMATCH=y -> Rebuilds everything. This doesn't occur before the offending commit. So it only happens when specifying extra environment variables on the command line. So I can get rid of the rebuilding by making my scripts less strict by removing CONFIG_DEBUG_SECTION_MISMATCH=y. But is this really correct? Two last examples with more detail: make[1]: Entering directory `/home/linus/linux/build-u300' CHK include/config/kernel.release GEN ./Makefile CHK include/generated/uapi/linux/version.h CHK include/generated/utsrelease.h Using .. as source for kernel make[2]: `include/generated/mach-types.h' is up to date. CALL ../scripts/checksyscalls.sh - due to target missing CHK include/generated/compile.h Kernel: arch/arm/boot/Image is ready Kernel: arch/arm/boot/zImage is ready make[1]: Leaving directory `/home/linus/linux/build-u300' make -f Makefile -j5 ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- KBUILD_OUTPUT=build-u300 zImage CONFIG_DEBUG_SECTION_MISMATCH=y V=2 make[1]: Entering directory `/home/linus/linux/build-u300' CHK include/config/kernel.release GEN ./Makefile CHK include/generated/uapi/linux/version.h CHK include/generated/utsrelease.h Using .. as source for kernel CC scripts/mod/empty.o - due to command line change CC scripts/mod/devicetable-offsets.s - due to command line change MKELF scripts/mod/elfconfig.h - due to: scripts/mod/empty.o HOSTCC scripts/mod/modpost.o - due to: scripts/mod/elfconfig.h HOSTCC scripts/mod/sumversion.o - due to: scripts/mod/elfconfig.h GEN scripts/mod/devicetable-offsets.h - due to: scripts/mod/devicetable-offsets.s HOSTCC scripts/mod/file2alias.o - due to: scripts/mod/elfconfig.h scripts/mod/devicetable-offsets.h HOSTLD scripts/mod/modpost - due to: scripts/mod/modpost.o scripts/mod/file2alias.o scripts/mod/sumversion.o make[2]: `include/generated/mach-types.h' is up to date. CC kernel/bounds.s - due to command line change GEN include/generated/bounds.h - due to: kernel/bounds.s CC arch/arm/kernel/asm-offsets.s - due to: include/generated/bounds.h GEN include/generated/asm-offsets.h - due to: arch/arm/kernel/asm-offsets.s CALL ../scripts/checksyscalls.sh - due to target missing CC init/main.o - due to: include/generated/bounds.h CC arch/arm/common/firmware.o - due to: include/generated/bounds.h CC arch/arm/mm/dma-mapping.o - due to: include/generated/bounds.h CC arch/arm/kernel/elf.o - due to: include/generated/bounds.h CC arch/arm/mach-u300/core.o - due to: include/generated/bounds.h AS arch/arm/kernel/entry-common.o - due to: include/generated/asm-offsets.h LD arch/arm/common/built-in.o - due to: arch/arm/common/firmware.o CHK include/generated/compile.h CC arch/arm/kernel/irq.o - due to: include/generated/bounds.h CC arch/arm/mach-u300/dummyspichip.o - due to: include/generated/bounds.h CC init/do_mounts.o - due to: include/generated/bounds.h CC arch/arm/mm/extable.o - due to: include/generated/bounds.h CC arch/arm/kernel/opcodes.o - due to: include/generated/bounds.h (...) If I revert commit f4d4ffc03efc: make[1]: Entering directory `/home/linus/linux/build-u300' CHK include/config/kernel.release GEN ./Makefile CHK include/generated/uapi/linux/version.h Using .. as source for kernel CHK include/generated/utsrelease.h make[2]: `include/generated/mach-types.h' is up to date. CC scripts/mod/empty.o - due to command line change CC scripts/mod/devicetable-offsets.s - due to command line change CALL ../scripts/checksyscalls.sh - due to target missing MKELF scripts/mod/elfconfig.h - due to: scripts/mod/empty.o HOSTCC scripts/mod/modpost.o - due to: scripts/mod/elfconfig.h HOSTCC scripts/mod/sumversion.o - due to: scripts/mod/elfconfig.h GEN scripts/mod/devicetable-offsets.h - due to: scripts/mod/devicetable-offsets.s HOSTCC scripts/mod/file2alias.o - due to: scripts/mod/elfconfig.h scripts/mod/devicetable-offsets.h HOSTLD scripts/mod/modpost - due to: scripts/mod/modpost.o scripts/mod/file2alias.o scripts/mod/sumversion.o CHK include/generated/compile.h Kernel: arch/arm/boot/Image is ready Kernel: arch/arm/boot/zImage is ready make[1]: Leaving directory `/home/linus/linux/build-u300' So in both cases a changed command line is detected and empty.o and devicetable-offsets.s is rebuilt. But after the commit the rebuild goes on to rebuild kernel/bounds.s which generates bounds.h which in turn rebuilds the whole world. I don't know why the behaviour changed like this :( Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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