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    SubjectRe: Problems with arm64 compat vdso
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    Hi Will,

    thank you for reporting this.

    On 20/09/2019 15:27, Will Deacon wrote:
    > Hi Vincenzo,
    >
    > I've been running into a few issues with the COMPAT vDSO. Please could
    > you have a look?
    >

    I will be at Linux Recipes next week. I will look at this with priority when I
    come back.

    > If I do the following:
    >
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig
    > [...]
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
    > [set CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"]
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
    >
    > Then I see the following warning:
    >
    > arch/arm64/Makefile:62: CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built
    >
    > even though the compat vDSO *has* been built:
    >
    > $ file arch/arm64/kernel/vdso32/vdso.so
    > arch/arm64/kernel/vdso32/vdso.so: ELF 32-bit LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, BuildID[sha1]=c67f6c786f2d2d6f86c71f708595594aa25247f6, stripped
    >
    > However, I also get some warnings because arm64 headers are being included
    > in the compat vDSO build:
    >
    > In file included from ./arch/arm64/include/asm/thread_info.h:17:0,
    > from ./include/linux/thread_info.h:38,
    > from ./arch/arm64/include/asm/preempt.h:5,
    > from ./include/linux/preempt.h:78,
    > from ./include/linux/spinlock.h:51,
    > from ./include/linux/seqlock.h:36,
    > from ./include/linux/time.h:6,
    > from /usr/local/google/home/willdeacon/work/linux/lib/vdso/gettimeofday.c:7,
    > from <command-line>:0:
    > ./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
    > ./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
    > u64 __addr = (u64)addr & ~__tag_shifted(0xff);
    > ^
    > In file included from ./arch/arm64/include/asm/pgtable-hwdef.h:8:0,
    > from ./arch/arm64/include/asm/processor.h:34,
    > from ./arch/arm64/include/asm/elf.h:118,
    > from ./include/linux/elf.h:5,
    > from ./include/linux/elfnote.h:62,
    > from arch/arm64/kernel/vdso32/note.c:11:
    > ./arch/arm64/include/asm/memory.h: In function ‘__tag_set’:
    > ./arch/arm64/include/asm/memory.h:233:15: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
    > u64 __addr = (u64)addr & ~__tag_shifted(0xff);
    > ^
    > Worse, if your compat binutils isn't up-to-date, you'll actually run into
    > a build failure:
    >
    > /tmp/ccFCrjUg.s:80: Error: invalid barrier type -- `dmb ishld'
    > /tmp/ccFCrjUg.s:124: Error: invalid barrier type -- `dmb ishld'
    >
    > There also appears to be a problem getting the toolchain prefix from Kconfig.
    > If, for example, I do:
    >
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- defconfig
    > [...]
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
    > [set CONFIG_CROSS_COMPILE_COMPAT_VDSO="vincenzo"]
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
    > arch/arm64/Makefile:64: *** vincenzogcc not found, check CROSS_COMPILE_COMPAT. Stop.
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- menuconfig
    > [set CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"]
    > $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu-
    > arch/arm64/Makefile:64: *** vincenzogcc not found, check CROSS_COMPILE_COMPAT. Stop.
    > $ grep CONFIG_CROSS_COMPILE_COMPAT_VDSO .config
    > CONFIG_CROSS_COMPILE_COMPAT_VDSO="arm-linux-gnueabihf-"
    >
    > which is irritating, because it seems to force a 'mrproper' if you don't
    > get the prefix right first time.
    >
    > Cheers,
    >
    > Will
    >

    --
    Regards,
    Vincenzo
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