Loads & Stores

Memory access instructions:

Loads (I-type):

• LB rd, offset(rs1): byte, sign-extend.
• LBU rd, offset(rs1): byte, zero-extend.
• LH rd, offset(rs1): halfword, sign-extend.
• LHU rd, offset(rs1): halfword, zero-extend.
• LW rd, offset(rs1): word.

Stores (S-type):

• SB rs2, offset(rs1): byte.
• SH rs2, offset(rs1): halfword.
• SW rs2, offset(rs1): word.

Address calculation: addr = rs1 + sign_extend(offset).

Implementation:

Storage:

Endianness: RISC-V is little-endian by default. Byte 0 is LSB.

Common patterns:

• Pointer dereference: LW with offset 0.
• Array access: ADDI to compute pointer + LW.
• Struct field: LW with offset = field's position in struct.

Function prologue uses stores:

addi sp, sp, -16    # allocate stack frame
sw   ra, 12(sp)     # save return address
sw   s0, 8(sp)      # save callee-saved
addi s0, sp, 16     # set frame pointer

Epilogue uses loads:

lw   s0, 8(sp)
lw   ra, 12(sp)
addi sp, sp, 16
ret