riscv-calling-convention.md

Register	ABI Name	Description	Saver
x0	zero	Hard-wired zero	—
x1	ra	Return address	Caller
x2	sp	Stack pointer	Callee
x3	gp	Global pointer	—
x4	tp	Thread pointer	—
x5–7	t0–2	Temporaries	Caller
x8	s0/fp	Saved register/frame pointer	Callee
x9	s1	Saved register	Callee
x10–11	a0–1	Function arguments/return values	Caller
x12–17	a2–7	Function arguments	Caller
x18–27	s2–11	Saved registers	Callee
x28–31	t3–6	Temporaries	Caller

RV32E Calling Convention

The RV32E calling convention is designed to be usable with the RV32E ISA.

This calling convention is the same as the integer calling convention, except for the following differences. The stack pointer need only be aligned to a 32-bit boundary.

Registers x16-x31 do not participate in the ABI, so there are only six argument registers, a0-a5, only two callee-saved registers, s0-s1, and only three temporaries, t0-t2.

If used with an ISA that has any of the registers x16-x31 and f0-f31, then these registers are considered temporaries.