sys: preprocessor successor module

[fabian18]

Contribution description

Generate a header file, containing successor definitions up to a fixed maximum.
This allows to use the preprocessor to compute the successor of a number and is useful to construct priority values for auto_init.
This is similar to boost preprocessor arithmetik.

Testing procedure

See usage in tests/external_module_dirs/external_modules/external_module/external_module.c

CFLAGS+=-DCONFIG_AUTO_INIT_ENABLE_DEBUG=1 BOARD=nucleo-f767zi make flash term

2022-07-06 09:39:31,837 # auto_init: ztimer_init (1010)
2022-07-06 09:39:31,840 # auto_init: auto_init_random (1040)
2022-07-06 09:39:31,844 # auto_init: auto_init_external_module (1041)
2022-07-06 09:39:31,847 # auto_init: auto_init_miot_mtd (1249)
2022-07-06 09:39:31,851 # auto_init: auto_init_miot_node (1359)
2022-07-06 09:39:31,860 # main(): This is RIOT! (Version: 2022.07-devel-788-g87bda-preprocessor_successor)
2022-07-06 09:39:31,862 # Message: Linking worked
2022-07-06 09:39:31,863 # Initialization worked!

Issues/PRs references

#18003

[fabian18]

@fjmolinas could be interested

[maribu]

I think this is useful for external modules to hook into the auto init code in a more robust fashion.

I think that @gdoffe and many @benpicco may be interested in this. IMO, this only needs a rebase to get in.

[benpicco]

I suppose

#define PRIO2 AUTO_INIT_PRIORITY_AFTER(PRIO)

would not work, right?

But even if limited to in-tree modules as reference, this already is a big improvement.

What if two external modules both chose UTO_INIT_PRIORITY_AFTER(AUTO_INIT_PRIO_MOD_RANDOM)?

[maribu]

The sorting is done by XFA alphabetically. The priorities just prefix numbers to the symbol name. So symbol 1337_foo would always come after 1337_bar, because b < f.

This may be good enough if both foo and bar really only care to be called after random is initialized and have no interdependencies.

[fabian18]

#define PRIO2 AUTO_INIT_PRIORITY_AFTER(PRIO)

That’s also possible. Note the priority is 1042 instead of 1041. And note the alphabetic order if some modules have the same priority.

diff --git a/tests/external_module_dirs/external_modules/external_module/external_module.c b/tests/external_module_dirs/external_modules/external_module/external_module.c
index f520d66631..351fa55526 100644
--- a/tests/external_module_dirs/external_modules/external_module/external_module.c
+++ b/tests/external_module_dirs/external_modules/external_module/external_module.c
@@ -23,9 +23,16 @@
 #include "auto_init_priorities.h"
 #include "auto_init_utils.h"
 
+void bauto_init_external_module(void)
+{
+    external_module_initialized = true;
+}
+
 #define PRIO AUTO_INIT_PRIORITY_AFTER(AUTO_INIT_PRIO_MOD_RANDOM)
+#define PRIO2 AUTO_INIT_PRIORITY_AFTER(PRIO)
 
-AUTO_INIT(auto_init_external_module, PRIO);
+AUTO_INIT(bauto_init_external_module, PRIO2);
+AUTO_INIT(auto_init_external_module, PRIO2);
 
 bool external_module_initialized = false;
 char *external_module_message = "Linking worked";

tests/external_module_dirs/bin/miot-nucleo-f767zi/tests_external_module_dirs.map

 .roxfa.auto_init_xfa.5_1042
                0x0000000008003cc0       0x18 /home/fabian/forks/RIOT/tests/external_module_dirs/bin/miot-nucleo-f767zi/external_module/external_module.o
                0x0000000008003cc0                auto_init_xfa_auto_init_external_module
                0x0000000008003ccc                auto_init_xfa_bauto_init_external_module

tests/external_module_dirs

Type '/exit' to exit.
2022-10-13 17:48:25,548 # auto_init: ztimer_init (1010)
2022-10-13 17:48:25,551 # auto_init: auto_init_random (1040)
2022-10-13 17:48:25,555 # auto_init: auto_init_external_module (1042)
2022-10-13 17:48:25,559 # auto_init: bauto_init_external_module (1042)
2022-10-13 17:48:25,562 # auto_init: auto_init_miot_mtd (1249)
2022-10-13 17:48:25,566 # auto_init: auto_init_miot_node (1359)
2022-10-13 17:48:25,573 # main(): This is RIOT! (Version: 2022.07-devel-790-g44a6e-preprocessor_successor)
2022-10-13 17:48:25,575 # Message: Linking worked
2022-10-13 17:48:25,577 # Initialization worked!
2022-10-13 17:48:49,627 # Exiting Pyterm

[benpicco]

Please rebase & squash

[fabian18]

Oops forgot the rebase ...

[benpicco]

This is some dark magic, but the benefits are clearly worth it.

[riot-ci]

Murdock results

✔️ PASSED

fefd8ba sys/preprocessor: add Kconfig file

Success	Failures	Total	Runtime
1983	0	1983	07m:47s

Artifacts

• Documentation preview

This only reflects a subset of all builds from https://ci-prod.riot-os.org. Please refer to https://ci.riot-os.org for a complete build for now.

[benpicco]

looks like KConfig is still missing

[benpicco]

Please squash!

[fabian18]

Thank You!