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The processor reads the item from the top of stack

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Unformatted text preview: gradation and in some instances program failures. 6.2.3 Address-Size Attributes for Stack Accesses Instructions that use the stack implicitly (such as the PUSH and POP instructions) have two address-size attributes each of either 16 or 32 bits. This is because they always have the implicit address of the top of the stack, and they may also have an explicit memory address (for example, PUSH Array1[EBX]). The attribute of the explicit address is determined by the D flag of the current code segment and the presence or absence of the 67H address-size prefix. The address-size attribute of the top of the stack determines whether SP or ESP is used for the stack access. Stack operations with an address-size attribute of 16 use the 16-bit SP stack pointer register and can use a maximum stack address of FFFFH; stack operations with an address-size attribute of 32 bits use the 32-bit ESP register and can use a maximum address of FFFFFFFFH. The default address-size attribute for data segments used as stacks is controlled by the B flag of the segment's descriptor. When this flag is clear, the default address-size attribute is 16; when the flag is set, the address-size attribute is 32. Vol. 1 6-3 PROCEDURE CALLS, INTERRUPTS, AND EXCEPTIONS 6.2.4 Procedure Linking Information The processor provides two pointers for linking of procedures: the stack-frame base pointer and the return instruction pointer. When used in conjunction with a standard software procedure-call technique, these pointers permit reliable and coherent linking of procedures. Stack-Frame Base Pointer The stack is typically divided into frames. Each stack frame can then contain local variables, parameters to be passed to another procedure, and procedure linking information. The stack-frame base pointer (contained in the EBP register) identifies a fixed reference point within the stack frame for the called procedure. To use the stack-frame base pointer, the called procedure typically copies the contents of the ESP register into the EBP register prior to pushing any local variables on the stack. The stack-frame base pointer then permits easy access to data structures passed on the stack, to the return instruction pointer, and to local variables added to the stack by the called procedure. Like the ESP register, the EBP register automatically points to an address in the current stack segment (that is, the segment specified by the current contents of the SS register). Return Instruction Pointer Prior to branching to the first instruction of the called procedure, the CALL instruction pushes the address in the EIP register onto the current stack. This address is then called the return-instruction pointer and it points to the instruction where execution of the calling procedure should resume following a return from the called procedure. Upon returning from a called procedure, the RET instruction pops the return-instruction pointer from the stack back into the EIP register. Execution of the ca...
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