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    Subject[PATCH 5.4 56/57] arm64: vdso: Add -fasynchronous-unwind-tables to cflags
    Date
    From: Vincenzo Frascino <vincenzo.frascino@arm.com>

    commit 1578e5d03112e3e9d37e1c4d95b6dfb734c73955 upstream.

    On arm64 linux gcc uses -fasynchronous-unwind-tables -funwind-tables
    by default since gcc-8, so now the de facto platform ABI is to allow
    unwinding from async signal handlers.

    However on bare metal targets (aarch64-none-elf), and on old gcc,
    async and sync unwind tables are not enabled by default to avoid
    runtime memory costs.

    This means if linux is built with a baremetal toolchain the vdso.so
    may not have unwind tables which breaks the gcc platform ABI guarantee
    in userspace.

    Add -fasynchronous-unwind-tables explicitly to the vgettimeofday.o
    cflags to address the ABI change.

    Fixes: 28b1a824a4f4 ("arm64: vdso: Substitute gettimeofday() with C implementation")
    Cc: Will Deacon <will@kernel.org>
    Reported-by: Szabolcs Nagy <szabolcs.nagy@arm.com>
    Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm64/kernel/vdso/Makefile | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/arm64/kernel/vdso/Makefile
    +++ b/arch/arm64/kernel/vdso/Makefile
    @@ -32,7 +32,7 @@ UBSAN_SANITIZE := n
    OBJECT_FILES_NON_STANDARD := y
    KCOV_INSTRUMENT := n

    -CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny
    +CFLAGS_vgettimeofday.o = -O2 -mcmodel=tiny -fasynchronous-unwind-tables

    ifneq ($(c-gettimeofday-y),)
    CFLAGS_vgettimeofday.o += -include $(c-gettimeofday-y)

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