arch: add armv8m

[damianloew]

Description

arch: add armv8m

Motivation and Context

Finalizing the nrf9160 basic port

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (nrf9160 devkit).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[github-actions]

Unit Test Results

7 155 tests  ±0   6 448 ✅ ±0   33m 43s ⏱️ -27s
  397 suites ±0     707 💤 ±0 
    1 files   ±0       0 ❌ ±0 

Results for commit 0faa598. ± Comparison against base commit 8e7daf8.

♻️ This comment has been updated with latest results.

[kemonats]

I have a small comment. I suggest adding a .cpu directive to each *.S file at its begining.

[damianloew]

I have a small comment. I suggest adding a .cpu directive to each *.S file at its begining.

Hmm, but those files are intended for various armv8 cpus, like Cortex-M23 and so on (I know that now they are not provided, but maybe they will be available in the future)

[agkaminski]

General remark - modify copyright headers. You are an author of all these files, of some (like Makefile) you are the only author

[agkaminski]

Alignment might cause some performance penalty. IMHO better to set it to 4, to make it predictable

[damianloew]

Do we want to leave 2 for other arm architectures?

[agkaminski]

Other arm archs aren't in the scope of this PR. Imho it's best to change alignment to 4 everywhere eventually, as @lukileczo found out it's faster indeed

[damianloew]

Oh I see that it has been changed recently

[agkaminski]

Redundant

Suggested change

.align 2

[agkaminski]

Suggested change

	__asm__ volatile(
	__asm__ volatile (

[damianloew]

Can we leave it without a space to be compliant with clang-format? Like for other architectures

[agkaminski]

I'd rather not, clang-format is confused in this case, as it thinks it's a function - it's not. It would be best to use clang-format off on every inline asm instead

[lukileczo]

With the merge of #347, I've created conflicts for your port again. I've made a good chunk of code previously split into armv7a and armv7m common - in arm directory, which has v7a and v7m subdirectories, so you can remove a fair amount of previously copied code from this PR.