XEND - Transactional End

Opcode/Instruction

Op/ En

64/32bit Mode Support

CPUID Feature Flag

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

Operand2

Operand3

Operand4

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
            RIP := fallbackRIP
       ELSE
            EIP := fallbackEIP
   FI;
END

Flags Affected

None.

Intel C/C++ Compiler Intrinsic Equivalent 

XEND void _xend( void );

SIMD Floating-Point Exceptions

None.

Other Exceptions

#UD

CPUID.(EAX=7, ECX=0):EBX.RTM[bit 11] = 0. If LOCK prefix is used.

#GP(0)

If RTM_ACTIVE = 0.