Typo: occured -> occurred

[lttng-tools.git] / include / lttng / session.h

diff --git a/include/lttng/session.h b/include/lttng/session.h
index 395df32450889d806aa0efd805a7a2cd67f4c219..9b2d7eb414a8500ff7319f1f79164125f4c289d7 100644 (file)
--- 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().