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Store Register Byte (immediate) stores the least significant byte of a 32-bit register to memory. The address that is used for the store is calculated from a base register and an immediate offset. For information about memory accesses, see Load/Store addressing modes.
It has encodings from 3 classes: Post-index , Pre-index and Unsigned offset
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | imm9 | 0 | 1 | Rn | Rt | ||||||||||||||||
size | opc |
boolean wback = TRUE; boolean postindex = TRUE; integer scale = UInt(size); bits(64) offset = SignExtend(imm9, 64);
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | imm9 | 1 | 1 | Rn | Rt | ||||||||||||||||
size | opc |
boolean wback = TRUE; boolean postindex = FALSE; integer scale = UInt(size); bits(64) offset = SignExtend(imm9, 64);
31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
0 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | imm12 | Rn | Rt | |||||||||||||||||||
size | opc |
boolean wback = FALSE; boolean postindex = FALSE; integer scale = UInt(size); bits(64) offset = LSL(ZeroExtend(imm12, 64), scale);
For information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly STRB (immediate).
<Wt> | Is the 32-bit name of the general-purpose register to be transferred, encoded in the "Rt" field. |
<Xn|SP> | Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field. |
<simm> | Is the signed immediate byte offset, in the range -256 to 255, encoded in the "imm9" field. |
<pimm> | Is the optional positive immediate byte offset, in the range 0 to 4095, defaulting to 0 and encoded in the "imm12" field. |
integer n = UInt(Rn); integer t = UInt(Rt); AccType acctype = AccType_NORMAL; MemOp memop; boolean signed; integer regsize; if opc<1> == '0' then // store or zero-extending load memop = if opc<0> == '1' then MemOp_LOAD else MemOp_STORE; regsize = if size == '11' then 64 else 32; signed = FALSE; else if size == '11' then UNDEFINED; else // sign-extending load memop = MemOp_LOAD; if size == '10' && opc<0> == '1' then UNDEFINED; regsize = if opc<0> == '1' then 32 else 64; signed = TRUE; integer datasize = 8 << scale; boolean tag_checked = memop != MemOp_PREFETCH && (wback || n != 31); boolean wb_unknown = FALSE; boolean rt_unknown = FALSE; if memop == MemOp_LOAD && wback && n == t && n != 31 then c = ConstrainUnpredictable(Unpredictable_WBOVERLAPLD); assert c IN {Constraint_WBSUPPRESS, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_WBSUPPRESS wback = FALSE; // writeback is suppressed when Constraint_UNKNOWN wb_unknown = TRUE; // writeback is UNKNOWN when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction(); if memop == MemOp_STORE && wback && n == t && n != 31 then c = ConstrainUnpredictable(Unpredictable_WBOVERLAPST); assert c IN {Constraint_NONE, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_NONE rt_unknown = FALSE; // value stored is original value when Constraint_UNKNOWN rt_unknown = TRUE; // value stored is UNKNOWN when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction();
if HaveMTE2ExtHaveMTEExt() then
SetTagCheckedInstruction(tag_checked);
bits(64) address;
bits(datasize) data;
if n == 31 then
if memop != MemOp_PREFETCH then CheckSPAlignment();
address = SP[];
else
address = X[n];
if ! postindex then
address = address + offset;
case memop of
when MemOp_STORE
if rt_unknown then
data = bits(datasize) UNKNOWN;
else
data = X[t];
Mem[address, datasize DIV 8, acctype] = data;
when MemOp_LOAD
data = Mem[address, datasize DIV 8, acctype];
if signed then
X[t] = SignExtend(data, regsize);
else
X[t] = ZeroExtend(data, regsize);
when MemOp_PREFETCHPrefetch(address, t<4:0>);
if wback then
if wb_unknown then
address = bits(64) UNKNOWN;
elsif postindex then
address = address + offset;
if n == 31 then
SP[] = address;
else
X[n] = address;
If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.
Internal version only: isa v32.13v32.12, AdvSIMD v29.05v29.04, pseudocode v2020-12v2020-09_xml, sve v2020-12v2020-09_rc2b
; Build timestamp: 2020-12-16T142020-09-30T19:4116
Copyright © 2010-2020 Arm Limited or its affiliates. All rights reserved. This document is Non-Confidential.
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