Intel ITANIUM ARCHITECTURE - SOFTWARE DEVELOPERS MANUAL VOLUME 1 REV 2.3 Manual page 1355

CALL—Call Procedure (Continued)
FI;
IF stack segment selector is null THEN #TS(stack segment selector); FI;
IF stack segment selector index is not within its descriptor table limits
THEN #TS(SS selector); FI
Read code segment descriptor;
IF stack segment selector's RPL  DPL of code segment
OR stack segment DPL  DPL of code segment
OR stack segment is not a writable data segment
IF stack segment not present THEN #SS(SS selector); FI;
IF CallGateSize = 32
THEN
ELSE (* CallGateSize = 16 *)
FI;
CPL  CodeSegment(DPL)
CS(RPL)  CPL
END;
SAME-PRIVILEGE:
IF CallGateSize = 32
THEN
Volume 4: Base IA-32 Instruction Reference
TSSstackAddress  new code segment (DPL  4) + 2
IF (TSSstackAddress + 4)  TSS limit
THEN #TS(current TSS selector); FI;
newESP  TSSstackAddress;
newSS  TSSstackAddress + 2;
THEN #TS(SS selector); FI
IF stack does not have room for parameters plus 16 bytes
THEN #SS(SS selector); FI;
IF CallGate(InstructionPointer) not within code segment limit THEN #GP(0); FI;
SS  newSS;
(* segment descriptor information also loaded *)
ESP  newESP;
CS:EIP  CallGate(CS:InstructionPointer);
(* segment descriptor information also loaded *)
Push(oldSS:oldESP); (* from calling procedure *)
temp  parameter count from call gate, masked to 5 bits;
Push(parameters from calling procedure's stack, temp)
Push(oldCS:oldEIP); (* return address to calling procedure *)
IF stack does not have room for parameters plus 8 bytes
THEN #SS(SS selector); FI;
IF (CallGate(InstructionPointer) AND FFFFH) not within code segment limit
THEN #GP(0); FI;
SS  newSS;
(* segment descriptor information also loaded *)
ESP  newESP;
CS:IP  CallGate(CS:InstructionPointer);
(* segment descriptor information also loaded *)
Push(oldSS:oldESP); (* from calling procedure *)
temp  parameter count from call gate, masked to 5 bits;
Push(parameters from calling procedure's stack, temp)
Push(oldCS:oldEIP); (* return address to calling procedure *)
IF stack does not have room for 8 bytes
THEN #SS(0); FI;
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