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 abrodkin@synopsys.com Cc: stable@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