Add support for IDLE Thread stack allocator

Add a stack allocator hook specifically for allocation of IDLE thread stacks.
This allows the user to decide if IDLE thread stacks are statically allocated
or handled by the same custom allocator mechanism as other thread stacks.

Closes #4524.

2 files changed, 29 insertions, 5 deletions

diff --git a/cpukit/include/rtems/confdefs/percpu.h b/cpukit/include/rtems/confdefs/percpu.h
index badb616988..3bea8340cb 100644
--- a/cpukit/include/rtems/confdefs/percpu.h
+++ b/cpukit/include/rtems/confdefs/percpu.h
@@ -134,11 +134,19 @@ RTEMS_DEFINE_GLOBAL_SYMBOL(
 
 const size_t _Thread_Idle_stack_size = CONFIGURE_IDLE_TASK_STACK_SIZE;
 
-char _Thread_Idle_stacks[
-  _CONFIGURE_MAXIMUM_PROCESSORS
-    * ( CONFIGURE_IDLE_TASK_STACK_SIZE + CPU_IDLE_TASK_IS_FP * CONTEXT_FP_SIZE )
-] RTEMS_ALIGNED( CPU_INTERRUPT_STACK_ALIGNMENT )
-RTEMS_SECTION( ".rtemsstack.idle" );
+/*
+ * If the user provides a custom idle stack allocator, then we do not need
+ * memory reserved for the stacks but the symbol is still referenced in
+ * threadcreateidle.c. The code path just never uses it. Make it minimal
+ * size to proceed.
+ */
+#ifndef CONFIGURE_TASK_STACK_ALLOCATOR_FOR_IDLE
+  char _Thread_Idle_stacks[
+    _CONFIGURE_MAXIMUM_PROCESSORS
+      * ( CONFIGURE_IDLE_TASK_STACK_SIZE + CPU_IDLE_TASK_IS_FP * CONTEXT_FP_SIZE )
+  ] RTEMS_ALIGNED( CPU_INTERRUPT_STACK_ALIGNMENT )
+  RTEMS_SECTION( ".rtemsstack.idle" );
+#endif
 
 #if defined(CONFIGURE_IDLE_TASK_INITIALIZES_APPLICATION) && \
   !defined(CONFIGURE_IDLE_TASK_BODY)
diff --git a/cpukit/include/rtems/confdefs/wkspace.h b/cpukit/include/rtems/confdefs/wkspace.h
index 1db4f2d09d..82de8633bf 100644
--- a/cpukit/include/rtems/confdefs/wkspace.h
+++ b/cpukit/include/rtems/confdefs/wkspace.h
@@ -167,12 +167,14 @@ const uintptr_t _Stack_Space_size = _CONFIGURE_STACK_SPACE_SIZE;
   #pragma GCC diagnostic ignored "-Wpragmas"
   #pragma GCC diagnostic ignored "-Wtautological-pointer-compare"
 
+  /* Custom allocator may or may not use the work space. */ 
   #ifdef CONFIGURE_TASK_STACK_ALLOCATOR_AVOIDS_WORK_SPACE
     const bool _Stack_Allocator_avoids_workspace = true;
   #else
     const bool _Stack_Allocator_avoids_workspace = false;
   #endif
 
+  /* Custom allocator may or may not need initialization. */
   #ifdef CONFIGURE_TASK_STACK_ALLOCATOR_INIT
     const Stack_Allocator_initialize _Stack_Allocator_initialize =
       _CONFIGURE_ASSERT_NOT_NULL(
@@ -187,6 +189,7 @@ const uintptr_t _Stack_Space_size = _CONFIGURE_STACK_SPACE_SIZE;
     );
   #endif
 
+  /* Custom allocator must include allocate and free */
   const Stack_Allocator_allocate _Stack_Allocator_allocate =
     _CONFIGURE_ASSERT_NOT_NULL(
       Stack_Allocator_allocate,
@@ -200,11 +203,24 @@ const uintptr_t _Stack_Space_size = _CONFIGURE_STACK_SPACE_SIZE;
     );
 
   #pragma GCC diagnostic pop
+
+/*
+ * Must provide both a custom stack allocator and deallocator
+ */
 #elif defined(CONFIGURE_TASK_STACK_ALLOCATOR) \
   || defined(CONFIGURE_TASK_STACK_DEALLOCATOR)
   #error "CONFIGURE_TASK_STACK_ALLOCATOR and CONFIGURE_TASK_STACK_DEALLOCATOR must be both defined or both undefined"
 #endif
 
+/*
+ * Custom IDLE thread stacks allocator. If this is provided, it is assumed
+ * that the allocator is providing its own memory for these stacks.
+ */
+#ifdef CONFIGURE_TASK_STACK_ALLOCATOR_FOR_IDLE
+  const Stack_Allocator_allocate_for_idle _Stack_Allocator_allocate_for_idle =
+    CONFIGURE_TASK_STACK_ALLOCATOR_FOR_IDLE;
+#endif
+
 #ifdef CONFIGURE_DIRTY_MEMORY
   RTEMS_SYSINIT_ITEM(
     _Memory_Dirty_free_areas,