Why some kernels are in C and others in Assembly?

[Do Po]

Hello,

I was wondering what is the reason for having written some kernels in C with inline assembly (like most x86_64 kernels) and others in full assembly (like arm64 ones). Is there some fundamental reason?

Best,

Dumitru

[martin-frbg]

Sorry for the very late reply - no fundamental reason (at least that I know of), just code produced by multiple developers over more than ten years - individual coding styles and preferences for readability, possibly kernels starting out as pure C and later getting only the important parts rewritten in assembly. Some of the more recent additions are now using intrinsics as a middle ground, something that simply was not available in earlier times.

Best,

Martin