[컴퓨터구조] Procedure Calling

caller calls callee

 

Set register x10(a0) - x17(a7) with the arguments in order before caling the function.

(8 registers)

If the function takes more than 8 arguments, the rest of the arguments are passed to the callee using memory.

 

RISC-V calle convention is designed to pass only one value from callee to caller

<Return Value>

Use register x10(a0) - x11(a1)

x10 [31:0]

x11 [63: 32]

If we do not have to use a0, a1 after calling a function,

we can reuse a0, a1 register to send the result back to the caller

-> can save registers, use registers for other optimization

 

If the return value is larger than 64-bit, the return value is passed through memory.

 

<Prodecure Call Instrucitons>

Procedure call: jump-and-link instruction

jal x1, ProcedureLabel

jumps to the target address

save the address of the next instruction in x1

x1's register name is ra (return address)

x1: store return address

 

Procedure return: jump-and-link register instruction

jalr x0, offset(x2)

x0: save return address, x2: basic address

jump to offset + address in x2

address of the next instruction -> x0