tree 7160561793bbaf2b5a1a27a5fbed1c6f36eede87
parent 8ad3a5ddaf71be6e57ea19f6d84b8b111b06755f
author Andre Przywara <andre.przywara@arm.com> 1675783265 +0000
committer Tom Rini <trini@konsulko.com> 1678148674 -0500

riscv: semihosting: replace inline assembly with assembly file

So far we used inline assembly to inject the actual instruction that
triggers the semihosting service. While this sounds elegant, as it's
really only about a few instructions, it has some serious downsides:
- We need some barriers in place to force the compiler to issue writes
  to a data structure before issuing the trap instruction.
- We need to convince the compiler to actually fill the structures that
  we use pointers to.
- We need a memory clobber to avoid the compiler caching the data in
  those structures, when semihosting writes data back.
- We need register arguments to make sure the function ID and the
  pointer land in the right registers.

This is all doable, but fragile and somewhat cumbersome. Since we now
have a separate function in an extra file anyway, we can do away with
all the magic and just write that in an actual assembler.
This is much more readable and robust.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>