gdb_server, rtos: Fine-grained RTOS register access

1. Add get_thread_reg() to rtos. It's used in rtos_get_gdb_reg() to read
the value of a single register, instead of reading all register values
by calling get_thread_reg_list().
2. Add set_reg() to rtos. gdb_server uses this to change a single
register value for a specific thread.
3. Add target_get_gdb_reg_list_noread() so it's possible for gdb to get
a list of registers without attempting to read their contents.

The clang static checker doesn't find any new problems with this change.

Change-Id: I77f792d1238cb015b91527ca8cb99593ccc8870e
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: http://openocd.zylin.com/5114
Tested-by: jenkins
Reviewed-by: Matthias Welwarsky <matthias@welwarsky.de>

src/target/register.c

@@ -36,6 +36,29 @@
  * may be separate registers associated with debug or trace modules.
  */
 
+struct reg *register_get_by_number(struct reg_cache *first,
+		uint32_t reg_num, bool search_all)
+{
+	unsigned i;
+	struct reg_cache *cache = first;
+
+	while (cache) {
+		for (i = 0; i < cache->num_regs; i++) {
+			if (cache->reg_list[i].exist == false)
+				continue;
+			if (cache->reg_list[i].number == reg_num)
+				return &(cache->reg_list[i]);
+		}
+
+		if (search_all)
+			cache = cache->next;
+		else
+			break;
+	}
+
+	return NULL;
+}
+
 struct reg *register_get_by_name(struct reg_cache *first,
 		const char *name, bool search_all)
 {

src/target/register.h

@@ -159,6 +159,8 @@ struct reg_arch_type {
 	int (*set)(struct reg *reg, uint8_t *buf);
 };
 
+struct reg *register_get_by_number(struct reg_cache *first,
+		uint32_t reg_num, bool search_all);
 struct reg *register_get_by_name(struct reg_cache *first,
 		const char *name, bool search_all);
 struct reg_cache **register_get_last_cache_p(struct reg_cache **first);

src/target/target.c

@@ -1215,7 +1215,24 @@ int target_get_gdb_reg_list(struct target *target,
 		struct reg **reg_list[], int *reg_list_size,
 		enum target_register_class reg_class)
 {
-	return target->type->get_gdb_reg_list(target, reg_list, reg_list_size, reg_class);
+	int result = target->type->get_gdb_reg_list(target, reg_list,
+			reg_list_size, reg_class);
+	if (result != ERROR_OK) {
+		*reg_list = NULL;
+		*reg_list_size = 0;
+	}
+	return result;
+}
+
+int target_get_gdb_reg_list_noread(struct target *target,
+		struct reg **reg_list[], int *reg_list_size,
+		enum target_register_class reg_class)
+{
+	if (target->type->get_gdb_reg_list_noread &&
+			target->type->get_gdb_reg_list_noread(target, reg_list,
+				reg_list_size, reg_class) == ERROR_OK)
+		return ERROR_OK;
+	return target_get_gdb_reg_list(target, reg_list, reg_list_size, reg_class);
 }
 
 bool target_supports_gdb_connection(struct target *target)
@@ -1587,8 +1604,9 @@ int target_call_event_callbacks(struct target *target, enum target_event event)
 		target_call_event_callbacks(target, TARGET_EVENT_GDB_HALT);
 	}
 
-	LOG_DEBUG("target event %i (%s)", event,
-			Jim_Nvp_value2name_simple(nvp_target_event, event)->name);
+	LOG_DEBUG("target event %i (%s) for core %s", event,
+			Jim_Nvp_value2name_simple(nvp_target_event, event)->name,
+			target_name(target));
 
 	target_handle_event(target, event);
 

src/target/target.h

@@ -502,6 +502,16 @@ int target_get_gdb_reg_list(struct target *target,
 		struct reg **reg_list[], int *reg_list_size,
 		enum target_register_class reg_class);
 
+/**
+ * Obtain the registers for GDB, but don't read register values from the
+ * target.
+ *
+ * This routine is a wrapper for target->type->get_gdb_reg_list_noread.
+ */
+int target_get_gdb_reg_list_noread(struct target *target,
+		struct reg **reg_list[], int *reg_list_size,
+		enum target_register_class reg_class);
+
 /**
  * Check if @a target allows GDB connections.
  *

src/target/target_type.h

@@ -111,6 +111,13 @@ struct target_type {
 	int (*get_gdb_reg_list)(struct target *target, struct reg **reg_list[],
 			int *reg_list_size, enum target_register_class reg_class);
 
+	/**
+	 * Same as get_gdb_reg_list, but doesn't read the register values.
+	 * */
+	int (*get_gdb_reg_list_noread)(struct target *target,
+			struct reg **reg_list[], int *reg_list_size,
+			enum target_register_class reg_class);
+
 	/* target memory access
 	* size: 1 = byte (8bit), 2 = half-word (16bit), 4 = word (32bit)
 	* count: number of items of <size>