inline asm semantics: output constraint width smaller than input

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Best regards,

Hi Ingo,

Could you describe what are the semantics you need for inline asm
constraints in the kernel?
GCC doesn't document all the corner cases, and defining inline asm =
"whatever gcc accepts" is not very useful for LLVM.

So far we've encountered the problem with input/output operand tied to
same register, but having different widths:
- output wider than input, both integers: do you need this case?
- output narrower than input, both integers: this is the common case, right?
- can it also happen that input is pointer, output is integer of
different width?
- .. any other mismatches?

Could you also describe why put_user/the example from pcbios needs the
different widths?

Best regards,