[v5,08/39] mbuf: use C11 alignas

Message ID 1708715054-22386-9-git-send-email-roretzla@linux.microsoft.com (mailing list archive)
State Superseded, archived
Delegated to: Thomas Monjalon
Series use C11 alignas |


Context Check Description
ci/checkpatch success coding style OK

Commit Message

Tyler Retzlaff Feb. 23, 2024, 7:03 p.m. UTC
  The current location used for __rte_aligned(a) for alignment of types
and variables is not compatible with MSVC. There is only a single
location accepted by both toolchains.

For variables standard C11 offers alignas(a) supported by conformant
compilers i.e. both MSVC and GCC.

For types the standard offers no alignment facility that compatibly
interoperates with C and C++ but may be achieved by relocating the
placement of __rte_aligned(a) to the aforementioned location accepted
by all currently supported toolchains.

To allow alignment for both compilers do the following:

* Move __rte_aligned from the end of {struct,union} definitions to
  be between {struct,union} and tag.

  The placement between {struct,union} and the tag allows the desired
  alignment to be imparted on the type regardless of the toolchain being
  used for all of GCC, LLVM, MSVC compilers building both C and C++.

* Replace use of __rte_aligned(a) on variables/fields with alignas(a).

Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
 lib/mbuf/rte_mbuf_core.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)


diff --git a/lib/mbuf/rte_mbuf_core.h b/lib/mbuf/rte_mbuf_core.h
index 5688683..917a811 100644
--- a/lib/mbuf/rte_mbuf_core.h
+++ b/lib/mbuf/rte_mbuf_core.h
@@ -463,7 +463,7 @@  enum {
  * The generic rte_mbuf, containing a packet mbuf.
-struct rte_mbuf {
+struct __rte_cache_aligned rte_mbuf {
 	RTE_MARKER cacheline0;
 	void *buf_addr;           /**< Virtual address of segment buffer. */
@@ -476,7 +476,7 @@  struct rte_mbuf {
 	 * same mbuf cacheline0 layout for 32-bit and 64-bit. This makes
 	 * working on vector drivers easier.
-	rte_iova_t buf_iova __rte_aligned(sizeof(rte_iova_t));
+	alignas(sizeof(rte_iova_t)) rte_iova_t buf_iova;
 	 * Next segment of scattered packet.
@@ -662,7 +662,7 @@  struct rte_mbuf {
 	uint16_t timesync;
 	uint32_t dynfield1[9]; /**< Reserved for dynamic fields. */
-} __rte_cache_aligned;
  * Function typedef of callback to free externally attached buffer.