Ensure sp is 16-byte aligned

Signed-off-by: Chien Wong <m@xv97.com>

Fix setting incorrect sp if single-hart

Signed-off-by: Chien Wong <m@xv97.com>

Signed-off-by: Chien Wong <m@xv97.com>

If single-hart is enabled, the sp is set to _stack_start - _hart_stack_size,
rather than _stack_start. Fix this.

Fixes: 9a02223a

 ("Add feature single-hart")
Signed-off-by: Chien Wong <m@xv97.com>

Ignore hartid in single-hart mode.

Don't bother checking hart ID on startup in single-hart mode. Allows
use of cores with unusual mhartid values and saves a few instructions.

Remove label-check from merge_group

It seems that the action used to check forbidden labels only works for PRs. Removing it from merge_group.

Check CHANGELOG.md on PRs to master

Implement r0 crate in assembly

This implements the `r0::init_data` and `r0::zero_bss` routines in
assembly. There is a generic implementation for `riscv32` and
`riscv64`, since `riscv64` deals with alignment problems. The routines
are kept at their old calling site so that only one hardware thread
calls them. Consequently they are also inlined into the `start_rust`
function.

[Issue #122]

Added GH action to check clippy

Add feature single-hart

Signed-off-by: Chien Wong <m@xv97.com>

Use inline assembly instead of pre-compiled blobs

Fix oor branch via linking

Temporary fix for OOR branch