microkernel: add task pointer list

Due to similar padding issue as pipe, the list of task object
may not be used directly. As mentioned before, some compiler/linker
may pad the large struct. For example, compiling under gcc and
march=i686 pads the struct to 32-byte alignment (march=atom to
64-byte alignment). This causes issue with sizeof() and pointer
arithmetic because they have no idea about the padding.
When the stars align in a certain way, these task structs may be
corrupted. So add a task pointer list and use it for task
manipulation. The task list remains as it is beneficial to group
them together to take advantage of cache locality.

Change-Id: I0e86bfe05742040f4540d7854c1ac14e76162776
Signed-off-by: Daniel Leung <daniel.leung@intel.com>

include/arch/arm/cortex_m/scripts/linker.cmd

@@ -203,6 +203,16 @@ SECTIONS
 		_k_task_list_end = .;
 	} GROUP_LINK_IN(RAMABLE_REGION)
 
+	SECTION_PROLOGUE (_k_task_ptr, (OPTIONAL),)
+	{
+		_k_task_ptr_start = .;
+			*(._k_task_ptr.public.*)
+			*(._k_task_ptr.private.*)
+			*(._k_task_ptr.idle.*)
+		KEEP(*(SORT_BY_NAME("._k_task_ptr*")))
+		_k_task_ptr_end = .;
+	} GROUP_LINK_IN(RAMABLE_REGION)
+
 	SECTION_PROLOGUE (_k_pipe_ptr, (OPTIONAL),)
 	{
 		_k_pipe_ptr_start = .;

include/arch/x86/linker-common-sections.h

@@ -174,6 +174,16 @@ SECTIONS
 		_k_task_list_end = .;
 	} GROUP_LINK_IN(RAM)
 
+	SECTION_PROLOGUE (_k_task_ptr, (OPTIONAL),)
+	{
+		_k_task_ptr_start = .;
+			*(._k_task_ptr.public.*)
+			*(._k_task_ptr.private.*)
+			*(._k_task_ptr.idle.*)
+		KEEP(*(SORT_BY_NAME("._k_task_ptr*")))
+		_k_task_ptr_end = .;
+	} GROUP_LINK_IN(RAM)
+
 	SECTION_PROLOGUE (_k_pipe_ptr, (OPTIONAL),)
 	{
 		_k_pipe_ptr_start = .;

include/microkernel/task.h

@@ -338,7 +338,9 @@ extern void task_group_leave(uint32_t groups);
 			(ktask_t)&_k_task_obj_##name, \
 			priority, 0x00000001, groups, \
 			entry, &__stack_##name[0], stack_size, NULL); \
-	const ktask_t name = (ktask_t)&_k_task_obj_##name;
+	const ktask_t name \
+		__section(_k_task_ptr, private, task) = \
+		(ktask_t)&_k_task_obj_##name;
 
 #ifdef __cplusplus
 }

kernel/microkernel/k_task.c

@@ -42,8 +42,8 @@
 #include <nano_private.h>
 #include <start_task_arch.h>
 
-extern struct k_task _k_task_list_start[];
+extern ktask_t _k_task_ptr_start[];
-extern struct k_task _k_task_list_end[];
+extern ktask_t _k_task_ptr_end[];
 
 
 ktask_t task_id_get(void)
@@ -342,6 +342,7 @@ void _k_task_group_op(struct k_args *A)
 	ktask_group_t grp = A->args.g1.group;
 	int opt = A->args.g1.opt;
 	struct k_task *X;
+	ktask_t *task_id;
 
 #ifdef CONFIG_TASK_DEBUG
 	if (opt == TASK_GROUP_BLOCK)
@@ -350,7 +351,9 @@ void _k_task_group_op(struct k_args *A)
 		_k_debug_halt = 0;
 #endif
 
-	for (X = _k_task_list_start; X < _k_task_list_end; X++) {
+	for (task_id = _k_task_ptr_start; task_id < _k_task_ptr_end;
+	     task_id++) {
+		X = (struct k_task *)(*task_id);
 		if (X->group & grp) {
 			switch (opt) {
 			case TASK_GROUP_START:

scripts/sysgen

@@ -405,7 +405,10 @@ def kernel_main_c_tasks():
             "    {NULL, NULL, %d, (ktask_t)&%s,\n" % (prio, obj_name) +
             "     0x00000001, %#010x,\n" % (group_bitmask) +
             "     %s, %s, %d,\n" % (entry, stack, size) +
-            "     (taskabortfunction)NULL, NULL};\n")
+            "     (taskabortfunction)NULL, NULL};\n" +
+            "ktask_t _k_task_ptr_%s " % (name) +
+            "    __section(_k_task_ptr, public, task) = " +
+            "    (ktask_t)&%s;\n" % (obj_name))
 
     kernel_main_c_out(
         "struct k_task _k_task_idle " +
@@ -414,7 +417,10 @@ def kernel_main_c_tasks():
         "     0x00000000, 0x00000000,\n" +
         "     (taskstartfunction)NULL, main_task_stack,\n"
         "     CONFIG_MAIN_STACK_SIZE,\n" +
-        "     (taskabortfunction)NULL, NULL};\n")
+        "     (taskabortfunction)NULL, NULL};\n" +
+        "ktask_t _k_task_ptr_idle " +
+        "    __section(_k_task_ptr, idle, task) = " +
+        "    (ktask_t)&_k_task_idle;\n")
 
     # currently scheduled task (idle task)