move compression buffer alloc to shutdown time

darshan-runtime/darshan-core.h

@@ -48,7 +48,7 @@ struct darshan_core_runtime
     struct darshan_core_record_ref *rec_hash;
     int rec_count;
     struct darshan_core_module* mod_array[DARSHAN_MAX_MODS];
-    char comp_buf[DARSHAN_COMP_BUF_SIZE];
+    char *comp_buf;
     double wtime_offset;
     char *trailing_data;
 };

darshan-runtime/lib/darshan-core.c

@@ -282,6 +282,13 @@ void darshan_core_shutdown()
     final_core = darshan_core;
     darshan_core = NULL;
 
+    final_core->comp_buf = malloc(DARSHAN_COMP_BUF_SIZE);
+    if(!(final_core->comp_buf))
+    {
+        darshan_core_cleanup(final_core);
+        return;
+    }
+
     /* we also need to set which modules were registered on this process and
      * call into those modules and give them a chance to perform any necessary
      * pre-shutdown steps.