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Add MSR, MRS instructions #23

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63 changes: 63 additions & 0 deletions instrs-sys.sail
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Original file line number Diff line number Diff line change
Expand Up @@ -100,4 +100,67 @@ function clause execute ExceptionReturn() = {
};
PSTATE = new_pstate;
}

/* MRS/MSR: Move to/from System Register */
/* is_read: true = MRS (read from system register), false = MSR (write to system register) */
union clause ast = SystemRegisterMove : (bool, bits(3), bits(4), bits(4), bits(3), reg_index)

val decodeSystemRegisterMove :
(bool, bits(3), bits(4), bits(4), bits(3), bits(5)) -> option(ast)

/* MRS: 1101 0101 0011 op1 CRn CRm op2 Rt (L=1) */
/* MSR: 1101 0101 0001 op1 CRn CRm op2 Rt (L=0) */
function clause decode (0b1101010100@[L]@0b11@(op1:bits(3))@(CRn:bits(4))@(CRm:bits(4))@(op2:bits(3))@(Rt:bits(5))) = {
decodeSystemRegisterMove(L == bitone, op1, CRn, CRm, op2, Rt)
}

function decodeSystemRegisterMove(is_read, op1, CRn, CRm, op2, Rt) = {
Some(SystemRegisterMove(is_read, op1, CRn, CRm, op2, unsigned(Rt)))
}

/* Lookup system register by encoding */
val lookup_sys_reg : (bits(3), bits(4), bits(4), bits(3)) -> option(register(bits(64)))
function lookup_sys_reg(op1, CRn, CRm, op2) = {
match (op1, CRn, CRm, op2) {
(0b000, 0b0001, 0b0000, 0b000) => Some(ref SCTLR_EL1),
(0b000, 0b0010, 0b0000, 0b000) => Some(ref TTBR0_EL1),
(0b000, 0b0010, 0b0000, 0b001) => Some(ref TTBR1_EL1),
(0b000, 0b0010, 0b0000, 0b010) => Some(ref TCR_EL1),
(0b000, 0b0100, 0b0000, 0b000) => Some(ref SPSR_EL1),
(0b000, 0b0100, 0b0000, 0b001) => Some(ref ELR_EL1),
(0b000, 0b0101, 0b0010, 0b000) => Some(ref ESR_EL1),
(0b000, 0b0110, 0b0000, 0b000) => Some(ref FAR_EL1),
(0b000, 0b0111, 0b0100, 0b000) => Some(ref PAR_EL1),
(0b000, 0b1100, 0b0000, 0b000) => Some(ref VBAR_EL1),
_ => None()
}
}

/* TODO: System register access should use sys_reg_read/sys_reg_write outcomes
* instead of plain register access. Waiting for decision on identifier format. */
function clause execute SystemRegisterMove(is_read, op1, CRn, CRm, op2, t) = {
_PC = _PC + 4;
let sys_reg_opt = lookup_sys_reg(op1, CRn, CRm, op2);
match sys_reg_opt {
Some(reg_ref) => {
if is_read then {
/* MRS Xt, <reg> - read from system register */
/* TODO: use sys_reg_read outcome */
X(t) = *reg_ref
} else {
/* MSR <reg>, Xt - write to system register */
/* TODO: use sys_reg_write outcome */
*reg_ref = X(t)
}
},
None() =>
assert(false,
concat_str("Unsupported System Register: ", concat_str((if is_read then "MRS" else "MSR"),
concat_str(" op1=", concat_str(bits_str(op1),
concat_str(" CRn=", concat_str(bits_str(CRn),
concat_str(" CRm=", concat_str(bits_str(CRm),
concat_str(" op2=", concat_str(bits_str(op2),
concat_str(" Rt=", dec_str(t)))))))))))))
}
}
$endif