[ovs-dev] [PATCH 1/2] ofp-actions: Make struct ofpact constant size across implementations.

Ben Pfaff blp at nicira.com
Tue Aug 12 18:44:09 UTC 2014


Before commit c2d936a44fa6 (ofp-actions: Centralize all OpenFlow action
code for maintainability.), struct ofpact was 4 bytes with GCC and Clang,
and 12 bytes with other compilers.  That commit changed struct ofpact so
that it remained 4 bytes with GCC and Clang but shrank to 8 bytes on other
compilers.  An unexpected side effect of that change was that the size
of the pad[] array in struct ofpact_nest shrank to 0 bytes, because that
array padded to a multiple of 8 bytes.  MSVC does not support 0-element
arrays, so this caused a build failure.

This commit fixes the problem by changing struct ofpact so that it is 4
bytes with every compiler.

Reported-by: Alin Serdean <aserdean at cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp at nicira.com>
---
 lib/compiler.h    |    1 +
 lib/ofp-actions.h |   12 ++++++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/lib/compiler.h b/lib/compiler.h
index cfe9066..e8bf119 100644
--- a/lib/compiler.h
+++ b/lib/compiler.h
@@ -169,6 +169,7 @@
  * or otherwise exposed outside of a single process. */
 #if __GNUC__ && !__CHECKER__
 #define OVS_PACKED_ENUM __attribute__((__packed__))
+#define HAVE_PACKED_ENUM
 #else
 #define OVS_PACKED_ENUM
 #endif
diff --git a/lib/ofp-actions.h b/lib/ofp-actions.h
index 0f1ea3f..5436f24 100644
--- a/lib/ofp-actions.h
+++ b/lib/ofp-actions.h
@@ -157,16 +157,20 @@ enum {
  *       code to translate the ofpact to OpenFlow must tolerate this case.)
  */
 struct ofpact {
+    /* We want the space advantage of an 8-bit type here on every
+     * implementation, without giving up the advantage of having a useful type
+     * on implementations that support packed enums. */
+#ifdef HAVE_PACKED_ENUM
     enum ofpact_type type;      /* OFPACT_*. */
+#else
+    uint8_t type;               /* OFPACT_* */
+#endif
+
     uint8_t raw;                /* Original type when added, if any. */
     uint16_t len;               /* Length of the action, in bytes, including
                                  * struct ofpact, excluding padding. */
 };
-
-#ifdef __GNUC__
-/* Make sure that OVS_PACKED_ENUM really worked. */
 BUILD_ASSERT_DECL(sizeof(struct ofpact) == 4);
-#endif
 
 /* Alignment. */
 #define OFPACT_ALIGNTO 8
-- 
1.7.10.4




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