X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=include%2Flttng%2Fsession.h;h=9b2d7eb414a8500ff7319f1f79164125f4c289d7;hb=499cbfa121fa1bc9ea78294f26b274b35fbc5e0a;hp=395df32450889d806aa0efd805a7a2cd67f4c219;hpb=780d4bb8ec9b4fa0ffd6d1ba2a2aa5d2f812611f;p=lttng-tools.git

diff --git a/include/lttng/session.h b/include/lttng/session.h
index 395df3245..9b2d7eb41 100644
--- a/include/lttng/session.h
+++ b/include/lttng/session.h
@@ -34,7 +34,7 @@ struct lttng_destruction_handle;
  *
  * The structures should be initialized to zero before use.
  */
-#define LTTNG_SESSION_PADDING1             12
+#define LTTNG_SESSION_PADDING1             8
 struct lttng_session {
 	char name[LTTNG_NAME_MAX];
 	/*
@@ -51,7 +51,29 @@ struct lttng_session {
 	uint32_t snapshot_mode;
 	unsigned int live_timer_interval;	/* usec */
 
+	/*
+	 * End of public attributes.
+	 * The remaining fields are used to deal with ABI management concerns.
+	 */
+
+	/*
+	 * 32-bit architectures are already naturally aligned on 4 bytes after
+	 * 'live_timer_interval'. However, the offset does not result in a
+	 * natural alignment on 64-bit architectures. Adding 4 bytes of
+	 * padding here results in an aligned offset after 'alignement_padding'
+	 * for both bitnesses.
+	 *
+	 * This was added since not all compilers appear to align unions in the
+	 * same way. Some (e.g. MSVC) do not seem to impose an alignement
+	 * constraint while others (e.g. gcc, clang, icc) seem to align it to
+	 * ensure 'ptr' is naturally aligned.
+	 */
+	char alignment_padding[4];
 	union {
+		/*
+		 * Ensure the 'extended' union has the same size for both
+		 * 32-bit and 64-bit builds.
+		 */
 		char padding[LTTNG_SESSION_PADDING1];
 		void *ptr;
 	} extended;
@@ -141,7 +163,7 @@ extern int lttng_destroy_session(const char *name);
  * an lttng_destruction_handle which can be used to wait for the completion
  * of the session's destruction. The lttng_destroy_handle can also be used
  * obtain the status and archive location of any implicit session
- * rotation that may have occured during the session's destruction.
+ * rotation that may have occurred during the session's destruction.
  *
  * Returns LTTNG_OK on success. The returned handle is owned by the caller
  * and must be free'd using lttng_destruction_handle_destroy().