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    SubjectRe: [PATCH] fix BUILD_BUG_ON() and a couple of bogus uses of it
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    From: Andrew Morton <akpm@linux-foundation.org>
    Date: Thu, 17 Sep 2009 16:24:37 -0700

    > sparc64:
    >
    > In file included from arch/sparc/kernel/vio.c:17:
    > /usr/src/devel/arch/sparc/include/asm/vio.h: In function `vio_dring_avail':
    > /usr/src/devel/arch/sparc/include/asm/vio.h:261: error: bit-field `<anonymous>' width not an integer constant
    >
    > static inline u32 vio_dring_avail(struct vio_dring_state *dr,
    > unsigned int ring_size)
    > {
    > BUILD_BUG_ON(!is_power_of_2(ring_size));
    >
    > return (dr->pending -
    > ((dr->prod - dr->cons) & (ring_size - 1)));
    > }
    >
    > changing it to MAYBE_BUILD_BUG_ON seems to have fixed it.

    That's completely bogus.

    First of all, arch/sparc/kernel/vio.c never calls this function
    so it should never be evaluated.

    Second of all, all the places that do call this function only
    pass pure constants as the 'ring_size' parameter.

    drivers/block/sunvdc.c:

    static inline u32 vdc_tx_dring_avail(struct vio_dring_state *dr)
    {
    return vio_dring_avail(dr, VDC_TX_RING_SIZE);
    }

    drivers/net/sunvnet.c:

    static inline u32 vnet_tx_dring_avail(struct vio_dring_state *dr)
    {
    return vio_dring_avail(dr, VNET_TX_RING_SIZE);
    }

    Making this MAYBE_BUILD_BUG_ON shouldn't be necessary.


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