sb

Store byte

This instruction is defined by:

  • I, version >= 0

This instruction is included in the following profiles:

  • MockProfile 64-bit Unpriv (Mandatory)

  • MockProfile 64-bit S-mode (Mandatory)

  • RVA20U64 (Mandatory)

  • RVA22U64 (Mandatory)

  • RVI20U32 (Mandatory)

  • RVI20U64 (Mandatory)

Encoding

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Assembly format

sb rs2, imm(rs1)

Synopsis

Store 8 bits of data from register rs2 to an address formed by adding rs1 to a signed offset.

Access

M HS U VS VU

Always

Always

Always

Always

Always

Decode Variables

Bits<12> imm = {$encoding[31:25], $encoding[11:7]};
Bits<5> rs2 = $encoding[24:20];
Bits<5> rs1 = $encoding[19:15];

Execution

  • IDL

  • Sail

XReg virtual_address = X[rs1] + imm;
write_memory<8>(virtual_address, X[rs2][7:0], $encoding);
{
  let offset : xlenbits = sign_extend(imm);
  /* Get the address, X(rs1) + offset.
     Some extensions perform additional checks on address validity. */
  match ext_data_get_addr(rs1, offset, Write(Data), width) {
    Ext_DataAddr_Error(e)  => { ext_handle_data_check_error(e); RETIRE_FAIL },
    Ext_DataAddr_OK(vaddr) =>
      if   check_misaligned(vaddr, width)
      then { handle_mem_exception(vaddr, E_SAMO_Addr_Align()); RETIRE_FAIL }
      else match translateAddr(vaddr, Write(Data)) {
        TR_Failure(e, _)    => { handle_mem_exception(vaddr, e); RETIRE_FAIL },
        TR_Address(paddr, _) => {
          let eares : MemoryOpResult(unit) = match width {
            BYTE   => mem_write_ea(paddr, 1, aq, rl, false),
            HALF   => mem_write_ea(paddr, 2, aq, rl, false),
            WORD   => mem_write_ea(paddr, 4, aq, rl, false),
            DOUBLE => mem_write_ea(paddr, 8, aq, rl, false)
          };
          match (eares) {
            MemException(e) => { handle_mem_exception(vaddr, e); RETIRE_FAIL },
            MemValue(_) => {
              let rs2_val = X(rs2);
              let res : MemoryOpResult(bool) = match (width) {
                BYTE => mem_write_value(paddr, 1, rs2_val[7..0],  aq, rl, false),
                HALF => mem_write_value(paddr, 2, rs2_val[15..0], aq, rl, false),
                WORD => mem_write_value(paddr, 4, rs2_val[31..0], aq, rl, false),
                DOUBLE if sizeof(xlen) >= 64
                     => mem_write_value(paddr, 8, rs2_val,        aq, rl, false),
                _    => report_invalid_width(__FILE__, __LINE__, width, "store"),
              };
              match (res) {
                MemValue(true)  => RETIRE_SUCCESS,
                MemValue(false) => internal_error(__FILE__, __LINE__, "store got false from mem_write_value"),
                MemException(e) => { handle_mem_exception(vaddr, e); RETIRE_FAIL }
              }
            }
          }
        }
      }
  }
}

Exceptions

This instruction may result in the following synchronous exceptions:

  • LoadAccessFault

  • StoreAmoAccessFault

  • StoreAmoAddressMisaligned

  • StoreAmoPageFault