Hello Joel,
this configuration option is a by product of the discussions related to
the proposed rtems_task_create_from_config() directive. I addresses an
issue with thread-local storage in dynamically linked objects. Since I
work currently in the same code area, it is easier if I try to implement
it instead of Chris.
https://lists.rtems.org/pipermail/devel/2020-September/061867.html
On 10/09/2020 16:40, Joel Sherrill wrote:
How is the user/system integrator supposed to figure out the size of
the TLS? It is not known until the application is linked and thus
varies based on the total set of code linked.
One way to figure out the TLS size is to link the executable and look at
the _TLS_Size symbol. We could also add an API function to get the size.
As far as I can tell, this makes this type of task creation unsuitable
for use in libraries where the end system is unknown.
Yes, the rtems_task_create_from_config() is unsuitable for general
purpose libraries.
It is at least fragile in tightly controlled applications and subject
to someone guessing a number larger than required which wastes memory
and goes against the intent of the statically allocated thread resources.
I talked with Chris today and we suggest to add this member to the task
configuration:
+ /**
+ * @brief This member defines the maximum thread-local storage size
supported
+ * by the task storage area.
+ *
+ * If the value is less than the actual thread-local storage size,
then the
+ * task creation by rtems_task_create_from_config() fails.
+ *
+ * If the value is less than the task storage area size, then the
task creation by
+ * rtems_task_create_from_config() fails.
+ */
+ size_t maximum_thread_local_storage_size;
So, if the task configuration doesn't match with the actual TLS size,
then you get run-time errors during task creation.
I work currently on a v4 of the rtems_task_create_from_config() patch.
If there is a practical and portable way to know this number, it needs
to be explained quite well in the documentation and always used in any
tests or examples.
The TLS size is only relevant if you use rtems_task_create_from_config()
or dynamically linked objects with thread-local storage. There is no
need to spread this stuff all over the place.
_______________________________________________
devel mailing list
devel@rtems.org
http://lists.rtems.org/mailman/listinfo/devel
