pkg/{littlefs,littlefs2}: fix unaligned memory accesses

[maribu]

Contribution description

This aligns the buffers in littlefs_desc_t / littlefs2_desc_t to fix hard faults on Cortex M0+ MCUs such as the samr21-xpro.

Testing procedure

• make BOARD=samr21-xpro -C tests/pkg_littlefs
• make BOARD=samr21-xpro -C tests/pkg_littlefs2

Issues/PRs references

Prior to #18141 the alignment requirement was met but luck. With this, the alignment requirement is now communicated to the compiler, which should fix future issues.

[kaspar030]

If it's an unaligned access, does it read/write whole words (or u16/u32)? In that case, wouldn't also a proper multiple be required, and thus probably a word (or u16/u32) typed buffer?

[kaspar030]

Anyhow, nice catch!

[maribu]

The uint8_t * buffer is casted to an uint32_t * pointer somewhere in the littlefs code, which is than accessed word-wise. Since all casts to pointers with higher alignment requirements have been removed from RIOT (or properly documented and other means of enforcement of the alignment employed), I believe the culprit is the littlefs API is asking for uint8_t * in their APIs. I haven't really looked into it, though.

Likely it is worth to use just uint32_t buffers and update all APIs in the way. But let's have this quick fix merged in the meantime. Green nightlies would be nice again :)

[maribu]

The sole failure is a CI glitch:

-- running on worker mobi7 thread 8, build number 3118.
make: Entering directory '/tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/tests/cpp_exclude'
make: Leaving directory '/tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/tests/cpp_exclude'
make: Entering directory '/tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/tests/cpp_exclude'
Building application "tests_cpp_exclude" for "arduino-mkrzero" with MCU "samd21".

sha1sum /tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/tests/cpp_exclude/tests/01-run.py /tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/build/tests_cpp_exclude.bin > /tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/build/test-input-hash.sha1
   text	   data	    bss	    dec	    hex	filename
  24368	    140	   4752	  29260	   724c	/tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/build/tests_cpp_exclude.elf
make: Leaving directory '/tmp/dwq.0.6613085980014425/17075f86ebbd7c6850b7f011c9f4afb8/tests/cpp_exclude'
0a1,3
> [INFO] Kconfiglib not found - getting it
> git-cache: cloning from cache. tag=commit061e71f7d78cb057762d88de088055361863deff-1619566
> [INFO] Kconfiglib downloaded
{"build/": 1864}

[MrKevinWeiss]

Darn. Ya, if someone who knows make better than me wants to take a look at #18470 we can fix those glitches. I want to just silence those commands but still fetch the package.