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In assembly language programming, the function prologue is a few lines of code at the beginning of a function, which prepare the stack and registers for use within the function. Similarly, the function epilogue appears at the end of the function, and restores the stack and registers to the state they were in before the function was called.
PUSH, POP, CALL and RET opcodes operate directly with the ESP d register. If ESP d is near overflow or the ESP register is referenced from other instructions (when ESP d ≠ 0), a synchronisation micro-op is inserted that updates the ESP O using the ALU and resets ESP d to 0.
The ability to push and pop FLAGS registers lets a program manipulate information in the FLAGS in ways for which machine-language instructions do not exist. For example, the cld and std instructions clear and set the direction flag (DF), respectively; but there is no instruction to complement DF. This can be achieved with the following assembly ...
Convert to an int16 (on the stack as int32) and throw an exception on overflow. Base instruction 0x83 conv.ovf.i2.un: Convert unsigned to an int16 (on the stack as int32) and throw an exception on overflow. Base instruction 0xB7 conv.ovf.i4: Convert to an int32 (on the stack as int32) and throw an exception on overflow. Base instruction 0x84
If a pop operation on the stack causes the stack pointer to move past the origin of the stack, a stack underflow occurs. If a push operation causes the stack pointer to increment or decrement beyond the maximum extent of the stack, a stack overflow occurs. Some environments that rely heavily on stacks may provide additional operations, for example:
In a system using x86 architecture, the instructions CLI (Clear Interrupt) and STI (Set Interrupt). The POPF (Pop Flags) removes a word from the stack into the FLAGS register, which may result in the Interrupt flag being set or cleared based on the bit in the FLAGS register from the top of the stack.