Add configUSE_MINI_LIST_ITEM configuration option to enable the MiniListItem_t type. (#433)

* Add configUSE_MINI_LIST_ITEM configuration option to enable the MiniListItem_t type.

When configUSE_MINI_LIST_ITEM == 0:
	MiniListItem_t and ListItem_t are both typedefs of struct xLIST_ITEM.

When configUSE_MINI_LIST_ITEM == 1 (the default in projdefs.h):
	MiniListItem_t is a typedef of struct xMINI_LIST_ITEM, which contains 3 fewer fields than a struct xLIST_ITEM.
	This configuration saves approximately sizeof(TickType_t) + 2 * sizeof( void * ) bytes of ram, however it also violates strict aliasing rules which some compilers depend on for optimization.

configUSE_MINI_LIST_ITEM defaults to 1 when not defined.

* Add pp_indent_brace option to uncrustify config

Improves compliance with the FreeRTOS code style guide:
https://www.freertos.org/FreeRTOS-Coding-Standard-and-Style-Guide.html

.github/uncrustify.cfg

@@ -157,4 +157,5 @@ pp_indent_at_level              = true     # false/true
 pp_indent_count                 = 4        # unsigned number
 pp_space                        = remove   # ignore/add/remove/force
 pp_if_indent_code               = true     # false/true
+pp_indent_brace                 = false    # true/false
 # option(s) with 'not default' value: 158

History.txt

@@ -7,6 +7,12 @@ Documentation and download available at https://www.FreeRTOS.org/
 	  The new function xTimerGetAutoReload() provides the auto-reload state as
 	  a BaseType_t.  The legacy function uxTimerGetAutoReload is retained with the
 	  original UBaseType_t return value.
+	+ Introduce the configUSE_MINI_LIST_ITEM configuration option. When this
+	  option is set to 1, ListItem_t and MiniLitItem_t remain separate types.
+	  However, when configUSE_MINI_LIST_ITEM == 0, MiniLitItem_t and ListItem_t
+	  are both typedefs of the same struct xLIST_ITEM. This addresses some issues
+	  observed when strict-aliasing and link time optimization are enabled.
+	  To maintain backwards compatibility, configUSE_MINI_LIST_ITEM defaults to 1.
 
 
 Changes between FreeRTOS V10.4.4 and FreeRTOS V10.4.5 released September 10 2021

include/FreeRTOS.h

@@ -334,6 +334,10 @@
     #define pcQueueGetName( xQueue )
 #endif
 
+#ifndef configUSE_MINI_LIST_ITEM
+    #define configUSE_MINI_LIST_ITEM    1
+#endif
+
 #ifndef portPOINTER_SIZE_TYPE
     #define portPOINTER_SIZE_TYPE    uint32_t
 #endif
@@ -1134,16 +1138,20 @@ struct xSTATIC_LIST_ITEM
 };
 typedef struct xSTATIC_LIST_ITEM StaticListItem_t;
 
-/* See the comments above the struct xSTATIC_LIST_ITEM definition. */
+#if ( configUSE_MINI_LIST_ITEM == 1 )
-struct xSTATIC_MINI_LIST_ITEM
+    /* See the comments above the struct xSTATIC_LIST_ITEM definition. */
-{
+    struct xSTATIC_MINI_LIST_ITEM
+    {
         #if ( configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES == 1 )
             TickType_t xDummy1;
         #endif
         TickType_t xDummy2;
         void * pvDummy3[ 2 ];
-};
+    };
-typedef struct xSTATIC_MINI_LIST_ITEM StaticMiniListItem_t;
+    typedef struct xSTATIC_MINI_LIST_ITEM StaticMiniListItem_t;
+#else /* if ( configUSE_MINI_LIST_ITEM == 1 ) */
+    typedef struct xSTATIC_LIST_ITEM      StaticMiniListItem_t;
+#endif /* if ( configUSE_MINI_LIST_ITEM == 1 ) */
 
 /* See the comments above the struct xSTATIC_LIST_ITEM definition. */
 typedef struct xSTATIC_LIST

include/list.h

@@ -153,14 +153,18 @@ struct xLIST_ITEM
 };
 typedef struct xLIST_ITEM ListItem_t;                   /* For some reason lint wants this as two separate definitions. */
 
-struct xMINI_LIST_ITEM
+#if ( configUSE_MINI_LIST_ITEM == 1 )
-{
+    struct xMINI_LIST_ITEM
+    {
         listFIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE /*< Set to a known value if configUSE_LIST_DATA_INTEGRITY_CHECK_BYTES is set to 1. */
         configLIST_VOLATILE TickType_t xItemValue;
         struct xLIST_ITEM * configLIST_VOLATILE pxNext;
         struct xLIST_ITEM * configLIST_VOLATILE pxPrevious;
-};
+    };
-typedef struct xMINI_LIST_ITEM MiniListItem_t;
+    typedef struct xMINI_LIST_ITEM MiniListItem_t;
+#else
+    typedef struct xLIST_ITEM      MiniListItem_t;
+#endif
 
 /*
  * Definition of the type of queue used by the scheduler.

list.c

@@ -54,6 +54,8 @@ void vListInitialise( List_t * const pxList )
      * as the only list entry. */
     pxList->pxIndex = ( ListItem_t * ) &( pxList->xListEnd ); /*lint !e826 !e740 !e9087 The mini list structure is used as the list end to save RAM.  This is checked and valid. */
 
+    listSET_FIRST_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );
+
     /* The list end value is the highest possible value in the list to
      * ensure it remains at the end of the list. */
     pxList->xListEnd.xItemValue = portMAX_DELAY;
@@ -63,6 +65,15 @@ void vListInitialise( List_t * const pxList )
     pxList->xListEnd.pxNext = ( ListItem_t * ) &( pxList->xListEnd );     /*lint !e826 !e740 !e9087 The mini list structure is used as the list end to save RAM.  This is checked and valid. */
     pxList->xListEnd.pxPrevious = ( ListItem_t * ) &( pxList->xListEnd ); /*lint !e826 !e740 !e9087 The mini list structure is used as the list end to save RAM.  This is checked and valid. */
 
+    /* Initialize the remaining fields of xListEnd when it is a proper ListItem_t */
+    #if ( configUSE_MINI_LIST_ITEM == 0 )
+    {
+        pxList->xListEnd.pvOwner = NULL;
+        pxList->xListEnd.pxContainer = NULL;
+        listSET_SECOND_LIST_ITEM_INTEGRITY_CHECK_VALUE( &( pxList->xListEnd ) );
+    }
+    #endif
+
     pxList->uxNumberOfItems = ( UBaseType_t ) 0U;
 
     /* Write known values into the list if