Commits on Mar 19, 2020

1. Support a .noinit section for variables …

   This is inspired by the linker sripts on the AVR architecture, which
   support a .noinit section (or any section starting with .noinit,
   actually) for variables that should be allocated an address in RAM, but
   not be initialized to any particular value (not even zero) on startup.
   These can then be used to remember values across resets.
   
   From the sketch perspective, this works exactly the same as on AVR: Just
   annote a global variable with `__attribute__((__section__(".noinit")))`
   and it will have an unpredictable value on power-up and retain its value
   during resets.
   
   To implement this without having to change all board-specific linker
   scripts, the linker commandline is changed to pass the board-specific
   linker script to the `--default-script` linker script, and change the
   main linker script (passed to `--script`, previously `-T`) to a generic
   "override" linker script. This new generic linker script contains an
   `INSERT BEFORE` command, which causes the linker to load it *in addition
   to* the default linker script, while adding an extra `.noinit` output
   section in the right place.
   
   Because these new variables take up RAM but have their own section in
   the .elf file, they should be accounted for in the size summary after
   compilation. This is done by adapting the `recipe.size.regex.data` entry
   to include this new section.

   

   matthijskooijman committed Mar 19, 2020
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