KICS! brainstorming

[Joel Sherrill]

On 7/22/2014 1:05 PM, Daniel Gutson wrote:
> Hi,
>
>    we are working in a very RAM constrained board, and noticed that
> some symbols could be moved to ROM by declaring them const.
>
> I have a slight idea about creating a consts-candidate detector tool
> "KICS!" (Keep It Const, St.! :) ), and wanted to hear some other
> people ideas.
>
> Initial thoughts:
>   - one approach could be a gdb script, in which we first read all the
> RAM memory of global objects after initialization (#1), and compare
> the memory at the end (#2), see what remained unchanged; this could
> throw many false positives but would be a starting point.
>
>   - another, I think tougher, is some pointer-tracking static analysis
> as a gcc plugin (not sure if it is even possible).
>
> Other ideas?
A couple other idea without knowing the BSP.

Turn on per function/data items sections. This has been done for the
SPARC BSPs
and had a pretty big impact on the size of the tests. I haven't heard
any reports
on real applications yet. This will require changing gcc and linking
flags and tinkering
with the linker script if it doesn't use * in all the right places for
pattern matching.

Put together a minimal version of your app. Basically just make the
calls you know
you need. Don't worry if it runs. Look through the symbol table and see
if there
are unexpected or undesired capabilities.  For example, some BSPs
unintentionally
put the printk() support in the same file with the real console driver.
Without
per-function sections, something calls printk() and end up with the
console driver
and termios.

If your application has lower requirements than what we think of as a
minimum,
we can refine our definition of minimum capabilities.

All of these are important to us as a project. Knowing unexpected
dependencies,
turning on per item sections, and lowering minimum capabilities based on
user
feedbac.
>
>
> (#1) after bsp_start? after rtems_initialize_data_structures?
>
> (#2) for some user-definition of "end", and/or after
> rtems_shutdown_executive or alike?
>
> Thanks!
>
>    Daniel.
>

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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