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INSTRUCTION SET REFERENCE
CALL—Call Procedure (Continued)
Mixing 16-Bit and 32-Bit Calls.
When making far calls between 16-bit and 32-bit code
segments, the calls should be made through a call gate. If the far call is from a 32-bit code
segment to a 16-bit code segment, the call should be made from the first 64 KBytes of the 32-
bit code segment. This is because the operand-size attribute of the instruction is set to 16, so only
a 16-bit return address offset is saved. Also, the call should be made using a 16-bit call gate so
that 16-bit values will be pushed on the stack. Refer to Chapter 17, Mixing 16-Bit and 32-Bit
Code, of the Intel Architecture Software DeveloperÂ’s Manual, Volume 3, for more information
on making calls between 16-bit and 32-bit code segments.
Operation
IF near call
THEN IF near relative call
IF the instruction pointer is not within code segment limit THEN #GP(0); FI;
THEN IF OperandSize = 32
THEN
IF stack not large enough for a 4-byte return address THEN #SS(0); FI;
Push(EIP);
EIP
<
EIP + DEST; (* DEST is rel32 *)
ELSE (* OperandSize = 16 *)
IF stack not large enough for a 2-byte return address THEN #SS(0); FI;
Push(IP);
EIP
<
(EIP + DEST) AND 0000FFFFH; (* DEST is rel16 *)
FI;
FI;
ELSE (* near absolute call *)
IF the instruction pointer is not within code segment limit THEN #GP(0); FI;
IF OperandSize = 32
THEN
IF stack not large enough for a 4-byte return address THEN #SS(0); FI;
Push(EIP);
EIP
<
DEST; (* DEST is r/m32 *)
ELSE (* OperandSize = 16 *)
IF stack not large enough for a 2-byte return address THEN #SS(0); FI;
Push(IP);
EIP
<
DEST AND 0000FFFFH; (* DEST is r/m16 *)
FI;
FI:
FI;
IF far call AND (PE = 0 OR (PE = 1 AND VM = 1)) (* real-address or virtual-8086 mode *)
THEN
IF OperandSize = 32
THEN
IF stack not large enough for a 6-byte return address THEN #SS(0); FI;
IF the instruction pointer is not within code segment limit THEN #GP(0); FI;
