Intel 253668-032US 用户手册

Vol. 3   5-27

PROTECTION

3. Checks the stack-segment descriptor for the proper privileges and type and 

generates an invalid TSS (#TS) exception if violations are detected.

4. Temporarily saves the current values of the SS and ESP registers.
5. Loads the segment selector and stack pointer for the new stack in the SS and ESP 

registers.

6. Pushes the temporarily saved values for the SS and ESP registers (for the calling 

procedure) onto the new stack (see Figure 5-13).

7. Copies the number of parameter specified in the parameter count field of the call 

gate from the calling procedure’s stack to the new stack. If the count is 0, no 
parameters are copied.

8. Pushes the return instruction pointer (the current contents of the CS and EIP 

registers) onto the new stack.

9. Loads the segment selector for the new code segment and the new instruction 

pointer from the call gate into the CS and EIP registers, respectively, and begins 
execution of the called procedure.

See the description of the CALL instruction in Chapter 3, Instruction Set Reference, in 
the IA-32 Intel Architecture Software Developer’s Manual, Volume 2, for a detailed 
description of the privilege level checks and other protection checks that the 
processor performs on a far call through a call gate.

The parameter count field in a call gate specifies the number of data items (up to 31) 
that the processor should copy from the calling procedure’s stack to the stack of the 
called procedure. If more than 31 data items need to be passed to the called proce-

Figure 5-13.  Stack Switching During an Interprivilege-Level Call

Parameter 1

Parameter 2

Parameter 3

Calling SS

Calling ESP

Parameter 1

Parameter 2

Parameter 3

Calling CS

Calling EIP

Called Procedure’s Stack

ESP

ESP

Calling Procedure’s Stack