On Fri, 6 Jul 2018, Alexey Brodkin wrote:
> It looks like on most of architectures "data" member of devres struture
> gets aligned to 8-byte "unsigned long long" boundary as one may expect:
> if we don't explicitly pack a structure then natural alignment
> (which matches each member data type) is used.
>
> But at least on 32-bit ARC architecture ABI requires "long long" types
> to be aligned by normal 32-bit word. This makes "data" field aligned to
> 12 bytes. This is still OK as long as we use 32-bit data only.
>
> But once we want to use native atomic64_t type (i.e. when we use special
> instructions LLOCKD/SCONDD for accessing 64-bit data) we easily hit
> misaligned access exception.
>
> That's because even on CPUs capable of non-aligned data access LL/SC
> instructions require strict alignment.
>
> Signed-off-by: Alexey Brodkin <abrod...@synopsys.com>
> Cc: sta...@vger.kernel.org
> ---
> drivers/base/devres.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> index f98a097e73f2..35ddc8b66bc9 100644
> --- a/drivers/base/devres.c
> +++ b/drivers/base/devres.c
> @@ -25,7 +25,7 @@ struct devres_node {
> struct devres {
> struct devres_node node;
> /* -- 3 pointers */
> - unsigned long long data[]; /* guarantee ull alignment */
Pretty please put a big fat comment here so that the innocent reader does
not start to wonder.
> + unsigned long long data[] __aligned(sizeof(unsigned long
> long));
> };
Thanks,
tglx
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