[PATCH v2] devres: Really align data field to unsigned long long - Linux-stable-mirror

8 Jul 2018

Depending on ABI "long long" type of a particular 32-bit CPU
might be aligned by either word (32-bits) or double word (64-bits).
Make sure "data" is really 64-bit aligned for any 32-bit CPU.
At least for 32-bit ARC cores ABI requires "long long" types
to be aligned by normal 32-bit word. This makes "data" field aligned to
12 bytes. Which 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: Thomas Gleixner tglx@linutronix.de
Cc: stable@vger.kernel.org
---
Changes v1 -> v2:
* Reworded commit message
 * Inserted comment right in source [Thomas]
drivers/base/devres.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/base/devres.c b/drivers/base/devres.c
index f98a097e73f2..466fa59c866a 100644
--- a/drivers/base/devres.c
+++ b/drivers/base/devres.c
@@ -24,8 +24,12 @@ struct devres_node {
struct devres {
    struct devres_node		node;
-	/* -- 3 pointers */
-	unsigned long long		data[];	/* guarantee ull alignment */
+	/*
+	 * Depending on ABI "long long" type of a particular 32-bit CPU
+	 * might be aligned by either word (32-bits) or double word (64-bits).
+	 * Make sure "data" is really 64-bit aligned for any 32-bit CPU.
+	 */
+	unsigned long long		data[] __aligned(sizeof(unsigned long long));
 };
struct devres_group {
-- 
2.17.1

    