GCSSTTR Guarded Control Stack unprivileged store This instruction stores a doubleword from a register to memory. The address that is used for the store is calculated from a base register. Explicit Memory effects produced by the instruction behave as if the instruction was executed at EL0 if the Effective value of PSTATE.UAO is 0 and either: The instruction is executed at EL1 and HCR_EL2.{NV, NV1} is not {1, 1}. The instruction is executed at EL2 when the Effective value of HCR_EL2.{E2H, TGE} is {1, 1}. Otherwise, the Explicit Memory effects operate with the restrictions determined by the Exception level at which the instruction is executed. 1 1 0 1 1 0 0 1 0 0 0 1 1 1 1 1 0 0 0 1 1 1 GCSSTTR <Xt>, [<Xn|SP>] if !IsFeatureImplemented(FEAT_GCS) then UNDEFINED; constant integer t = UInt(Rt); constant integer n = UInt(Rn); <Xt> Is the 64-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. bits(64) address; constant bits(2) effective_el = if AArch64.IsUnprivAccessPriv() then PSTATE.EL else EL0; if effective_el == PSTATE.EL then CheckGCSSTREnabled(); constant boolean privileged = effective_el != EL0; constant AccessDescriptor accdesc = CreateAccDescGCS(MemOp_STORE, privileged); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; Mem[address, 8, accdesc] = X[t, 64];