M[Addr] means a reference to the value stored in memory starting at address Addr.
The memory of address Addr could come from user space, CPU and MLU works together to get the physical page (PA) from Page Table, then access the PA in RAM.
RISC-V Integer Instructions
The operand forms is basically the same. lb D, Ssb S, D
Example: sd ra,40(sp) Save 8 bytes (double) from ra register to memory address of (sp + 40).
