[PATCH 06/13] config: Add rtems_malloc_task_stack_for_idle()

[Sebastian Huber]

On 30/09/2022 23:39, Chris Johns wrote:
> On 30/9/2022 7:21 pm, Sebastian Huber wrote:
>> Update #4524.
>> ---
>>   cpukit/doxygen/appl-config.h                | 13 +++++
>>   cpukit/include/rtems/rtems/config.h         | 29 +++++++++-
>>   cpukit/include/rtems/score/interr.h         |  1 +
>>   cpukit/sapi/src/interrtext.c                |  3 +-
>>   cpukit/sapi/src/malloctaskstackforidle.c    | 59 +++++++++++++++++++++
>>   spec/build/cpukit/librtemscpu.yml           |  1 +
>>   spec/build/testsuites/sptests/grp.yml       |  2 +
>>   spec/build/testsuites/sptests/spfatal36.yml | 19 +++++++
>>   testsuites/sptests/spfatal36/init.c         | 52 ++++++++++++++++++
>>   testsuites/sptests/spfatal36/spfatal36.doc  | 11 ++++
>>   testsuites/sptests/spinternalerror02/init.c |  2 +-
>>   testsuites/sptests/sptls04/init.c           |  2 +
>>   12 files changed, 191 insertions(+), 3 deletions(-)
>>   create mode 100644 cpukit/sapi/src/malloctaskstackforidle.c
>>   create mode 100644 spec/build/testsuites/sptests/spfatal36.yml
>>   create mode 100644 testsuites/sptests/spfatal36/init.c
>>   create mode 100644 testsuites/sptests/spfatal36/spfatal36.doc
>>
>> diff --git a/cpukit/doxygen/appl-config.h b/cpukit/doxygen/appl-config.h
>> index aa6dbae648..ee647dc961 100644
>> --- a/cpukit/doxygen/appl-config.h
>> +++ b/cpukit/doxygen/appl-config.h
>> @@ -4842,6 +4842,19 @@
>>    * configuration options.  It is assumed that any memory allocated for the
>>    * stack of an IDLE task will not be from the RTEMS Workspace or the memory
>>    * statically allocated by default.
>> + *
>> + * For applications with a thread-local storage size which is completely
>> + * unknown at the time the application configuration is defined, RTEMS provides
>> + * an IDLE task stack allocator which uses rtems_malloc().
> 
> I thought the TLS size was static and set by the linker? Has this changed?

No, this didn't change.

> 
> I am confused about the relationship between an unknown TLS size and IDLE task?
> And the relationship of the TLS size and stack size?

Currently, the IDLE task storage area is statically allocated. The size 
of this area is defined by CONFIGURE_IDLE_TASK_STACK_SIZE. So, this 
configuration option doesn't directly specify the IDLE task stack size. 
This size covers also the TLS area.

> 
>> * * The size of the
>> + * allocated thread storage area is the sum of stack size defined by the
>> + * #CONFIGURE_IDLE_TASK_STACK_SIZE configuration option and the actual
>> + * thread-local storage size of the application.
> 
> The label CONFIGURE_IDLE_TASK_STACK_SIZE provides no insight into it being
> effected by the TLS size.
> 
>> * * Define this configuration
>> + * option to ``rtems_malloc_task_stack_for_idle`` to use this allocator.  If
>> + * the memory allocation fails, then the system terminates with the
>> + * INTERNAL_ERROR_CORE fatal source and the
>> + * INTERNAL_ERROR_NO_MEMORY_FOR_IDLE_TASK_STACK fatal code during system
>> + * initialization.
>> + * @endparblock
> 
> I am confused about the how and why I would use this change?

With the statically allocated storage area for the IDLE task you need at 
least an estimate of the size if you define the application 
configuration. If you can't estimate it, then one option is to simply 
allocate it dynamically.

Maybe a better approach is to allocate the IDLE task storage from the 
workspace by default and use the CONFIGURE_IDLE_TASK_STACK_SIZE really 
for the stack size and not the complete storage area. We could add a new 
configuration option (for example CONFIGURE_IDLE_TASK_STORAGE_SIZE) to 
enable the static allocation.

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