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BLRAA, BLRAAZ, BLRAB, BLRABZ

Branch with link to register, with pointer authentication

This instruction authenticates the address in the general-purpose register that is specified by <Xn>, using a modifier and the specified key, and calls a subroutine at the authenticated address, setting register X30 to PC+4.

The modifier is:

Key A is used for BLRAA and BLRAAZ. Key B is used for BLRAB and BLRABZ.

If the authentication passes, the PE continues execution at the target of the branch. For information on behavior if the authentication fails, see Faulting on pointer authentication.

The authenticated address is not written back to the general-purpose register.

This instruction provides a hint that this is a subroutine call.

Integer class

(FEAT_PAuth)

313029282726252423222120191817161514131211109876543210
1101011Z0011111100001MRnRm
opop2A

Key A, register modifier encoding

(Z == 1 && M == 0)

BLRAA <Xn>, <Xm|SP>

Key A, zero modifier encoding

(Z == 0 && M == 0 && Rm == 11111)

BLRAAZ <Xn>

Key B, register modifier encoding

(Z == 1 && M == 1)

BLRAB <Xn>, <Xm|SP>

Key B, zero modifier encoding

(Z == 0 && M == 1 && Rm == 11111)

BLRABZ <Xn>

Decode (all encodings)

if !IsFeatureImplemented(FEAT_PAuth) then EndOfDecode(Decode_UNDEF); if Z == '0' && Rm != '11111' then EndOfDecode(Decode_UNDEF); constant integer n = UInt(Rn); constant integer m = UInt(Rm); constant boolean use_key_a = (M == '0'); constant boolean source_is_sp = ((Z == '1') && (m == 31)); constant boolean auth_then_branch = TRUE;

Assembler Symbols

<Xn>

Is the 64-bit name of the general-purpose register holding the address to be branched to, encoded in the "Rn" field.

<Xm|SP>

Is the 64-bit name of the general-purpose source register or stack pointer holding the modifier, encoded in the "Rm" field.

Operation

bits(64) target = X[n, 64]; constant bits(64) modifier = if source_is_sp then SP[64] else X[m, 64]; if use_key_a then target = AuthIA(target, modifier, auth_then_branch); else target = AuthIB(target, modifier, auth_then_branch); if IsFeatureImplemented(FEAT_GCS) && GCSPCREnabled(PSTATE.EL) then AddGCSRecord(PC64 + 4); // Value in BTypeNext will be used to set PSTATE.BTYPE BTypeNext = '10'; X[30, 64] = PC64 + 4; constant boolean branch_conditional = FALSE; BranchTo(target, BranchType_INDCALL, branch_conditional);

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