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RETAA, RETAB

Return from subroutine, with pointer authentication. This instruction authenticates the address that is held in LR, using SP as the modifier and the specified key, branches to the authenticated address, with a hint that this instruction is a subroutine return.

Key A is used for RETAA, and key B is used for RETAB.

If the authentication passes, the PE continues execution at the target of the branch. If the authentication fails, a Translation fault is generated.

The authenticated address is not written back to LR.

Integer
(ARMv8.3)

313029282726252423222120191817161514131211109876543210
110101100101111100001M1111111111
ZopARnRm

RETAA (M == 0)

RETAA

RETAB (M == 1)

RETAB

boolean use_key_a = (M == '0'); if !integer n =UInt(Rn); BranchType branch_type; integer m = UInt(Rm); boolean pac = (A == '1'); boolean use_key_a = (M == '0'); boolean source_is_sp = ((Z == '1') && (m == 31)); if !pac && m != 0 then UnallocatedEncoding(); elsif pac && !HavePACExt() then UnallocatedEncoding(); case op of when '00' branch_type = BranchType_JMP; when '01' branch_type = BranchType_CALL; when '10' branch_type = BranchType_RET; otherwise UnallocatedEncoding(); if pac then if Z == '0' && m != 31 then UnallocatedEncoding(); if branch_type == BranchType_RET() thenthen if n !=31 then UnallocatedEncoding();(); n = 30; source_is_sp = TRUE;

Operation

bits(64) target = X[30]; bits(64) modifier =[n]; if pac then bits(64) modifier = if source_is_sp then SP[]; if use_key_a then target =[] else X[m]; if use_key_a then target = AuthIA(target, modifier); else target = AuthIB(target, modifier);(target, modifier); if branch_type == BranchType_CALL then X[30] = PC[] + 4; BranchTo(target, BranchType_RET);(target, branch_type);


Internal version only: isa v29.05, AdvSIMD v26.0, pseudocode v35.3 ; Build timestamp: 2018-06-16T09:5845

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