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    SubjectRe: [PATCH net-next v2] geneve: Use empty braces for addr6 initializer
    On Mon, 12 Nov 2018 23:11:47 -0700
    Nathan Chancellor <natechancellor@gmail.com> wrote:

    > Clang warns:
    >
    > drivers/net/geneve.c:428:29: error: suggest braces around initialization
    > of subobject [-Werror,-Wmissing-braces]
    > struct in6_addr addr6 = { 0 };
    > ^
    > {}
    >
    > Most initializations of structs in the kernel seem to use this format.

    Actually, even with this, we get a warning with gcc 4.4 and 4.8. I tried a
    few compilers:

    $ gcc-4.4 --version | head -n1
    rhel-6.9-gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-18)
    $ gcc-4.8 --version | head -n1
    rhel-7.5-gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-28)
    $ gcc-7.3 --version | head -n1
    gcc-7.3-gcc (GCC) 7.3.0
    $ gcc-8.2 --version | head -n1
    gcc (Debian 8.2.0-9) 8.2.0
    $ clang --version | head -n1
    clang version 6.0.1-9.2 (tags/RELEASE_601/final)

    $ cat init.c
    #include <linux/in6.h>

    int main()
    {
    struct in6_addr addr6 = INIT;

    return addr6.in6_u.u6_addr8[0];
    }

    $ gcc-4.4 -DINIT="{ }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    init.c:5: warning: missing initializer
    $ gcc-4.4 -DINIT="{ 0 }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    init.c:5: warning: missing braces around initializer
    $ gcc-4.4 -DINIT="{ { { 0 } } }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1

    $ gcc-4.8 -DINIT="{ }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    init.c:5:16: warning: missing initializer for field 'in6_u' of 'struct in6_addr' [-Wmissing-field-initializers]
    $ gcc-4.8 -DINIT="{ 0 }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    init.c:5:16: warning: missing braces around initializer [-Wmissing-braces]
    $ gcc-4.8 -DINIT="{ { { 0 } } }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1

    $ gcc-7.3 -DINIT="{ }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    $ gcc-7.3 -DINIT="{ 0 }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    $ gcc-7.3 -DINIT="{ { { 0 } } }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1

    $ gcc-8.2 -DINIT="{ }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    $ gcc-8.2 -DINIT="{ 0 }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    $ gcc-8.2 -DINIT="{ { { 0 } } }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1

    $ clang -DINIT="{ }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    $ clang -DINIT="{ 0 }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1
    init.c:5:33: warning: suggest braces around initialization of subobject [-Wmissing-braces]
    $ clang -DINIT="{ { { 0 } } }" -S -Wall -Wextra -o init init.c 2>&1 | grep warning | head -n1

    So { { { 0 } } } seems to be the safest option. We could go with static
    but it looks even uglier to me.

    Joe, suggestions?

    --
    Stefano

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