Fix SIGBUS from alignment issues on 64bit ARM

ARMv8 (and in general aarch64) has flipped some strictness requirements.
However, at some point in history the NEED_ALIGN configure check code was
optimized away by GCC.

This fixes detection of alignment, as well as fixes an unaligned access that
snuck in via the logging code.

Also fixes a 64bit GCC atomics test that possibly never worked before.

configure.ac

@@ -490,13 +490,16 @@ AC_CHECK_FUNCS(clock_gettime)
 AC_CHECK_FUNCS([accept4], [AC_DEFINE(HAVE_ACCEPT4, 1, [Define to 1 if support accept4])])
 AC_CHECK_FUNCS([getopt_long], [AC_DEFINE(HAVE_GETOPT_LONG, 1, [Define to 1 if support getopt_long])])
 
+dnl Need to disable opt for alignment check. GCC is too clever and turns this
+dnl into wide stores and no cmp under O2.
 AC_DEFUN([AC_C_ALIGNMENT],
 [AC_CACHE_CHECK(for alignment, ac_cv_c_alignment,
 [
   AC_RUN_IFELSE(
     [AC_LANG_PROGRAM([
 #include <stdlib.h>
 #include <inttypes.h>
+#pragma GCC optimize ("O0")
     ], [
        char *buf = malloc(32);
 
@@ -551,7 +554,8 @@ dnl Check for usage of 64bit atomics
 dnl 32bit systems shouldn't have these.
 have_gcc_64atomics=no
 AC_MSG_CHECKING(for GCC 64bit atomics)
-AC_TRY_LINK([],[
+AC_TRY_LINK([#include <inttypes.h>
+   ],[
   uint64_t a;
   uint64_t b;
   b = __sync_add_and_fetch(&a, 1);

logger.c

@@ -363,7 +363,7 @@ static int logger_thread_read(logger *l, struct logger_stats *ls) {
         } else {
             logger_thread_write_entry(e, ls, scratch, scratch_len);
         }
-        pos += sizeof(logentry) + e->size;
+        pos += sizeof(logentry) + e->size + e->pad;
     }
     assert(pos <= size);
 
@@ -699,8 +699,9 @@ enum logger_ret_type logger_log(logger *l, const enum log_entry_type event, cons
         l->dropped++;
         return LOGGER_RET_NOSPACE;
     }
-    e->gid = logger_get_gid();
     e->event = d->subtype;
+    e->pad = 0;
+    e->gid = logger_get_gid();
     /* TODO: Could pass this down as an argument now that we're using
      * LOGGER_LOG() macro.
      */
@@ -754,8 +755,15 @@ enum logger_ret_type logger_log(logger *l, const enum log_entry_type event, cons
             break;
     }
 
+#ifdef NEED_ALIGN
+    /* Need to ensure *next* request is aligned. */
+    if (sizeof(logentry) + e->size % 8 != 0) {
+        e->pad = 8 - (sizeof(logentry) + e->size % 8);
+    }
+#endif
+
     /* Push pointer forward by the actual amount required */
-    if (bipbuf_push(buf, (sizeof(logentry) + e->size)) == 0) {
+    if (bipbuf_push(buf, (sizeof(logentry) + e->size + e->pad)) == 0) {
         fprintf(stderr, "LOGGER: Failed to bipbuf push a text entry\n");
         pthread_mutex_unlock(&l->mutex);
         return LOGGER_RET_ERR;

logger.h

@@ -100,6 +100,7 @@ struct logentry_item_store {
 
 typedef struct _logentry {
     enum log_entry_subtype event;
+    uint8_t pad;
     uint16_t eflags;
     uint64_t gid;
     struct timeval tv; /* not monotonic! */