Use of rtems_fdt_* and sp01

[Chris Johns]

On 20/11/2022 10:25 am, Joel Sherrill wrote:
> On Sat, Nov 19, 2022, 4:19 PM Chris Johns <chrisj at rtems.org
> <mailto:chrisj at rtems.org>> wrote:
> 
>     On 19/11/22 2:13 am, Joel Sherrill wrote:
>     > On Fri, Nov 18, 2022, 8:49 AM Kinsey Moore <kinsey.moore at oarcorp.com
>     <mailto:kinsey.moore at oarcorp.com>
>     > <mailto:kinsey.moore at oarcorp.com <mailto:kinsey.moore at oarcorp.com>>> wrote:
>     >     On Fri, Nov 18, 2022 at 12:44 AM Sebastian Huber
>     >     <sebastian.huber at embedded-brains.de
>     <mailto:sebastian.huber at embedded-brains.de>
>     >     <mailto:sebastian.huber at embedded-brains.de
>     <mailto:sebastian.huber at embedded-brains.de>>> wrote:
>     >         On 18/11/2022 06:32, Kinsey Moore wrote:
>     >         > On Thu, Nov 17, 2022 at 4:49 PM Chris Johns <chrisj at rtems.org
>     <mailto:chrisj at rtems.org>
>     >         <mailto:chrisj at rtems.org <mailto:chrisj at rtems.org>>
>     >         > <mailto:chrisj at rtems.org <mailto:chrisj at rtems.org>
>     <mailto:chrisj at rtems.org <mailto:chrisj at rtems.org>>>> wrote:
>     >         >
>     >         >     On 18/11/2022 2:39 am, Kinsey Moore wrote:
>     >         >      > I recently added FDT support to the AArch64 ZynqMP BSPs to
>     >         >     support an optional
>     >         >      > management console and managing ethernet parameters for
>     LibBSD.
>     >         >     Use of the
>     >         >      > rtems_fdt_* functions implies use of malloc which adds 4
>     bytes in
>     >         >     the TLS space.
>     >         >      > The sp01 test uses rtems_task_construct and specifies a
>     maximum
>     >         >     TLS size of 0
>     >         >      > bytes which causes a failure which the non-zero TLS size is
>     >         >     checked against the
>     >         >      > maximum TLS size of 0.
>     >         >
>     >         >     Does this mean there exists a requirement a BSPs cannot
>     internally
>     >         >     use the heap?
>     >         >
>     >         >
>     >         > That appears to be the case, at least practically. It works
>     fine, but it
>     >         > causes a test failure...
>     >
>     >         You can use the heap during system initialization. However, you should
>     >         avoid dependencies on errno, so instead of using malloc()/calloc() use
>     >         rtems_malloc()/rtems_calloc(). Independent of this, if the BSP
>     >         initialization can easily avoid the heap, then it should not use
>     the heap.
>     >
>     >         >
>     >         >
>     >         >     Maybe the test needs to be adjusted?
>     >         >
>     >         >
>     >         > That's part of why I sent this to the list. I was unsure whether
>     it was
>     >         > allowed or whether the test had bad assumptions baked into it.
>     >
>     >         The tests check specific aspects of the thread-local storage
>     support and
>     >         this works only if the BSP does not depend on TLS objects such as
>     errno.
>     >
>     >     This affects several other tests as well, so I guess my solution here is
>     >     either to alter the rtems_fdt_ wrappers to avoid dependencies on TLS or
>     >     proceed with the existing patch that uses the non-wrapped FDT functions.
>     >
>     > I agree with Sebastian that fixing the bsp is right.
>     >
>     > But also rtems_ fdt methods should be changed to use rtems_malloc. That would
>     > leave those methods useful. They are broken now for many intended use cases.
> 
>     We are currently reviewing the support for ftbo files in Linux (petalinux) with
>     a view to seeing how we can support them on RTEMS. I see FDT being use more and
>     more in RTEMS and with a number of different use cases and flows there is a need
>     to try and unify how we handle them. I see benefits if we can support a similar
>     dtbo model as Linux and if that happens the specific area in question in
>     rtems-fst can be move over to using it.
> 
> 
> FWIW Kinsey's patch to the rtems_fdt methods eliminated two coverity issues.

Yes and that is a worth while change. Thanks.

Chris