fs/shm/shmfs_alloc.c: Allocate zero-initialized memory in flat build

POSIX requires that the shm objects are zero-initialized. This has been broken
in some earlier commits (starting from 9af5fc5)

Also fix the flat build memory allocation to allocate both object data and payload
in the same chunk (as the comment also suggests). This saves allocations and memory
in a system with lots of shm objects.

Signed-off-by: Jukka Laitinen <[email protected]>

fs/shm/shmfs_alloc.c

@@ -51,24 +51,34 @@ FAR struct shmfs_object_s *shmfs_alloc_object(size_t length)
    * chunk in kernel heap
    */
 
-  object = fs_heap_zalloc(sizeof(struct shmfs_object_s));
-  if (object)
+  size_t alloc_size;
+  size_t cachesize = up_get_dcache_linesize();
+
+  if (cachesize > 0)
     {
-      size_t cachesize = up_get_dcache_linesize();
-      if (cachesize > 0)
+      alloc_size =
+        ALIGN_UP(sizeof(struct shmfs_object_s), cachesize) +
+        ALIGN_UP(length, cachesize);
+      object = fs_heap_memalign(cachesize, alloc_size);
+      if (object)
         {
-          object->paddr = fs_heap_memalign(cachesize,
-                                           ALIGN_UP(length, cachesize));
+          memset(object, 0, alloc_size);
+          object->paddr = (void *)((uintptr_t)object + cachesize);
         }
-      else
+    }
+  else
+    {
+      alloc_size = sizeof(struct shmfs_object_s) + length;
+      object = fs_heap_zalloc(alloc_size);
+      if (object)
         {
-          object->paddr = fs_heap_malloc(length);
+          object->paddr = (FAR char *)(object + 1);
         }
+    }
 
-      if (object->paddr)
-        {
-           allocated = true;
-        }
+  if (object->paddr)
+    {
+      allocated = true;
     }
 
 #elif defined(CONFIG_BUILD_PROTECTED)
@@ -152,9 +162,7 @@ void shmfs_free_object(FAR struct shmfs_object_s *object)
 {
   if (object)
     {
-#if defined(CONFIG_BUILD_FLAT)
-      fs_heap_free(object->paddr);
-#elif defined(CONFIG_BUILD_PROTECTED)
+#if defined(CONFIG_BUILD_PROTECTED)
       kumm_free(object->paddr);
 #elif defined(CONFIG_BUILD_KERNEL)
       size_t i;