xend

Transaction End

XEND

Specifies end of RTM region.

Details

Marks the end of a Restricted Transactional Memory (RTM) region and commits all buffered memory writes if the transaction succeeds. If the transaction has been aborted prior, XEND is a no-op; no flags are modified. Requires RTM extension and must be paired with XBEGIN.

Pseudocode Operation

if (RTM_TransactionActive) {
  if (RTMAborted) {
    // No-op; abort already occurred
  } else {
    // Commit buffered writes atomically
    CommitBufferedWrites();
    RTM_TransactionActive ← 0;
  }
  // No flags modified
}

Example

XEND

Encoding

Binary Layout

Format Legacy

Opcode NP 0F 01 D5

Extension RTM (TSX)

Operands

Reference (Intel® SDM)

Instruction Forms

Opcode	Instruction	Op/En	64/32-bit Mode	CPUID	Description
NP 0F 01 D5	XEND	A	V/V	RTM	Specifies the end of an RTM code region.

Instruction Operand Encoding

Op/En	Operand 1	Operand 2	Operand 3	Operand 4
A	N/A	N/A	N/A	N/A

Description

The instruction marks the end of an RTM code region. If this corresponds to the outermost scope (that is, including this XEND instruction, the number of XBEGIN instructions is the same as number of XEND instructions), the logical processor will attempt to commit the logical processor state atomically. If the commit fails, the logical processor will rollback all architectural register and memory updates performed during the RTM execution. The logical processor will resume execution at the fallback address computed from the outermost XBEGIN instruction. The EAX register is updated to reflect RTM abort information. Execution of XEND outside a transactional region causes a general-protection exception (#GP). Execution of XEND while in a suspend read address tracking region causes a transactional abort.

Operation

XEND
IF (RTM_ACTIVE = 0) THEN
SIGNAL #GP
ELSE
IF SUSLDTRK_ACTIVE = 1
THEN GOTO RTM_ABORT_PROCESSING;
FI;
RTM_NEST_COUNT--
IF (RTM_NEST_COUNT = 0) THEN
Try to commit transaction
IF fail to commit transactional execution
THEN
GOTO RTM_ABORT_PROCESSING;
ELSE (* commit success *)
RTM_ACTIVE := 0
FI;
FI;
FI;

(* For any RTM abort condition encountered during RTM execution *)
RTM_ABORT_PROCESSING:
Restore architectural register state
Discard memory updates performed in transaction
Update EAX with status
RTM_NEST_COUNT := 0
RTM_ACTIVE := 0
SUSLDTRK_ACTIVE := 0
IF 64-bit Mode
THEN


XEND—Transactional End                                                                                                                          Vol. 2D 6-33
RIP := fallbackRIP
ELSE
EIP := fallbackEIP
FI;
END

Intel C/C++ Compiler Intrinsic Equivalent

XEND void _xend( void );

Flags Affected

None.

Exceptions

SIMD Floating-Point Exceptions

None.

Other Exceptions

#UDCPUID.07H.00H:EBX.RTM[11] = 0. If LOCK prefix is used. #GP(0) If RTM_ACTIVE = 0. XEND—Transactional End Vol. 2D 6-34