cpu: make newlib_nano a DEFAULT_MODULE

[benpicco]

Contribution description

This allows to disable nanospecs with

DISABLE_MODULE += newlib_nano

if a full-features version of newlib is desired.

Testing procedure

examples/default

   text	   data	    bss	    dec	    hex	filename
  43144	    144	  18040	  61328	   ef90	/home/benpicco/dev/RIOT/examples/default/bin/same54-xpro/default.elf

examples/default with DISABLE_MODULE += newlib_nano

   text	   data	    bss	    dec	    hex	filename
  70748	   2520	  18084	  91352	  164d8	/home/benpicco/dev/RIOT/examples/default/bin/same54-xpro/default.elf

Issues/PRs references

[kfessel]

When i read the title i thought it was newlib (no nano) before and now it is newlib_nano by default.

But this is: it was always newlib_nano before, now it can be disabled

[benpicco]

How do I interpret this static test failure?

BOARDS_FEATURES_MISSING= "arduino-duemilanove newlib" "arduino-nano newlib" "arduino-uno newlib" "atmega1284p newlib" "derfmega128 newlib" "mega-xplained newlib" "microduino-corerf newlib" "native newlib" "waspmote-pro newlib" "zigduino newlib"
Makefile:23: *** The CI will never build for the following boards:  arduino-duemilanove arduino-nano arduino-uno atmega1284p derfmega128 mega-xplained microduino-corerf native waspmote-pro zigduino.  Stop.

I also wonder if we shouldn't just always select newlib_nano as a DEFAULT_MODULE.
Since it's a pseudomodule it won't do anything unless newlib is also selected, but it would reduce code duplication.

[maribu]

That test checks whether dependency tracking is able to determine that every board is buildable for hello word. With this PR, the AVR8 are detected to no longer be build-able, as the newlib feature is not provided by them.

I think that make info-boards-supported does not reset DEFAULT_MODULES after each board. Previously, that list was independent of the boards used. Since this no longer is the case, this Makefiles need to be fixed.

I'm pretty happy that we have that build system check now :-)

[benpicco]

Hm do you know where DEFAULT_MODULES should be reset?

[maribu]

Hm do you know where DEFAULT_MODULES should be reset?

Here:

RIOT/makefiles/info-global.inc.mk

Line 26 in efbd867

DEFAULT_MODULE := $(DEFAULT_MODULE_GLOBAL)

But as you see, this is already done. Maybe here is the issue:

RIOT/makefiles/info-global.inc.mk

Line 18 in efbd867

DEFAULT_MODULE_GLOBAL := $(DEFAULT_MODULE)

If DEFAULT_MODULE at the time no specific board is looked into already contains board-specific entries, things will break.

[maribu]

Out of curiosity: What is the use case for the non-nano version of newlib?

[fjmolinas]

ACK.

[fjmolinas]

ACK.

Will need #16435 to pass.

[maribu]

If I recall correctly, the static tests need a rebase to include upstream changes.