[PATCH v5 09/22] stack: fix unaligned accesses on 128-bit

[David Marchand]

Caught by UBSan:

../lib/eal/x86/include/rte_atomic_64.h:206:21: runtime error:
	member access within misaligned address 0x7ffd9c67f228 for
	type 'const rte_int128_t', which requires 16 byte alignment
	0x7ffd9c67f228: note: pointer points here
 00 00 00 00  c0 5d 3e 00 01 00 00 00  01 00 00 00 00 00 00 00
              ^
 00 00 00 00 00 00 00 00  00 00 00 00
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
	../lib/eal/x86/include/rte_atomic_64.h:206:21 in
	../lib/eal/x86/include/rte_atomic_64.h:206:21: runtime error:
	member access within misaligned address 0x7ffd9c67f228 for type
	'const union rte_int128_t::(anonymous at
	../lib/eal/include/generic/rte_atomic.h:1102:2)', which requires
	16 byte alignment
0x7ffd9c67f228: note: pointer points here
 00 00 00 00  c0 5d 3e 00 01 00 00 00  01 00 00 00 00 00 00 00
              ^
 00 00 00 00 00 00 00 00  00 00 00 00
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
	../lib/eal/x86/include/rte_atomic_64.h:206:21 in
	../lib/eal/x86/include/rte_atomic_64.h:206:16: runtime error:
	load of misaligned address 0x7ffd9c67f228 for type
	'const uint64_t' (aka 'const unsigned long'), which requires
	16 byte alignment
0x7ffd9c67f228: note: pointer points here
 00 00 00 00  c0 5d 3e 00 01 00 00 00  01 00 00 00 00 00 00 00
              ^
 00 00 00 00 00 00 00 00  00 00 00 00
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
	../lib/eal/x86/include/rte_atomic_64.h:206:21 in

Rather than explicitly set alignment in callers, mark the structure
itself with an alignment constraint.

Fixes: 3340202f5954 ("stack: add lock-free implementation")

Signed-off-by: David Marchand <david.marchand at redhat.com>
Acked-by: Bruce Richardson <bruce.richardson at intel.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev at huawei.com>
---
Changes since v4:
- dropped ABI exception and updated RN,

Changes since v3:
- changed rte_stack_lf_head struct alignment,

---

 doc/guides/rel_notes/release_25_11.rst | 3 +++
 lib/stack/rte_stack.h                  | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/doc/guides/rel_notes/release_25_11.rst b/doc/guides/rel_notes/release_25_11.rst
index ccad6d89ff..aa9211dd60 100644
--- a/doc/guides/rel_notes/release_25_11.rst
+++ b/doc/guides/rel_notes/release_25_11.rst
@@ -100,6 +100,9 @@ ABI Changes
    Also, make sure to start the actual text at the margin.
    =======================================================
 
+* stack: The structure ``rte_stack_lf_head`` alignment has been updated to 16 bytes
+  to avoid unaligned accesses.
+
 
 Known Issues
 ------------
diff --git a/lib/stack/rte_stack.h b/lib/stack/rte_stack.h
index 4439adfc42..fd17ac791d 100644
--- a/lib/stack/rte_stack.h
+++ b/lib/stack/rte_stack.h
@@ -33,14 +33,14 @@ struct rte_stack_lf_elem {
 	struct rte_stack_lf_elem *next;	/**< Next pointer */
 };
 
-struct rte_stack_lf_head {
+struct __rte_aligned(16) rte_stack_lf_head {
 	struct rte_stack_lf_elem *top; /**< Stack top */
 	uint64_t cnt; /**< Modification counter for avoiding ABA problem */
 };
 
 struct rte_stack_lf_list {
 	/** List head */
-	alignas(16) struct rte_stack_lf_head head;
+	struct rte_stack_lf_head head;
 	/** List len */
 	RTE_ATOMIC(uint64_t) len;
 };
-- 
2.50.0