| Message ID | 20180706171504.10265-1-abrodkin@synopsys.com |
|---|---|
| State | New |
| Headers | show |
| Series | devres: Really align data field to unsigned long long | expand |
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
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 */ + unsigned long long data[] __aligned(sizeof(unsigned long long)); }; struct devres_group {
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(-)