Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1356

CALL—Call Procedure (Continued)
ELSE (* CallGateSize = 16 *)
FI;
CS(RPL)  CPL
END;
TASK-GATE:
IF task gate DPL < CPL or RPL
THEN #GP(task gate selector);
FI;
IF task gate not present
THEN #NP(task gate selector);
FI;
IF Itanium System Environment THEN IA-32_Intercept(Gate,CALL);
Read the TSS segment selector in the task-gate descriptor;
IF TSS segment selector local/global bit is set to local
OR index not within GDT limits
FI;
Access TSS descriptor in GDT;
IF TSS descriptor specifies that the TSS is busy (low-order 5 bits set to 00001)
FI;
IF TSS not present
THEN #NP(TSS selector);
FI;
SWITCH-TASKS (with nesting) to TSS;
IF EIP not within code segment limit
THEN #GP(0);
FI;
END;
TASK-STATE-SEGMENT:
IF TSS DPL < CPL or RPL
ORTSS segment selector local/global bit is set to local
OR TSS descriptor indicates TSS not available
THEN #GP(TSS selector);
FI;
IF TSS is not present
THEN #NP(TSS selector);
FI;
IF Itanium System Environment THEN IA-32_Intercept(Gate,CALL);
SWITCH-TASKS (with nesting) to TSS
IF EIP not within code segment limit
4:54
IF EIP not within code segment limit then #GP(0); FI;
CS:EIP  CallGate(CS:EIP) (* segment descriptor information also loaded *)
Push(oldCS:oldEIP); (* return address to calling procedure *)
IF stack does not have room for parameters plus 4 bytes
THEN #SS(0); FI;
IF IP not within code segment limit THEN #GP(0); FI;
CS:IP  CallGate(CS:instruction pointer)
(* segment descriptor information also loaded *)
Push(oldCS:oldIP); (* return address to calling procedure *)
THEN #GP(TSS selector);
THEN #GP(TSS selector);
Volume 4: Base IA-32 Instruction Reference