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• Stack - a type of data structure where items are added and then removed in reverse order i.e. the most recently added item is the very first one that is removed.
• Stack - heavily used in programming for the storage of information during procedure or function calls.
• Push - Adding an item to a stack
• Pop - Removing an item from a stack
• The stack is implemented in reverse in memory
• Stack is implemented growing downward in memory.
• The RSP register is used to point to the current top of stack in memory.
• The basic stack operations of push and pop adjust the stack pointer register, RSP, during their operation.
• For push operation, the RSP register is decreased by 8.
• For push operation, the operand is copied to the stack at [RSP].
• For a pop operation, the current top of the stack, at [RSP], is copied into the operand.
• For a pop operation, the RSP register is increased by 8.
• Functions must be written before it can be used (located in the code segment).
• A function may be defined only once.
• There is no specific order required for how functions are defined.
• Functions cannot be nested.
• Function calls involve two main actions:

  • Linkage

  • Argument Transmission
• Linkage - the function must be able to return to the correct place in which it was originally called
• Argument Transmission - the function must be able to access parameters to operate on or to return results
• The linkage is about getting to and returning from a function call correctly.
• There are two instructions that handle the linkage:

  • call
  • ret
• call - transfers control to the named function
• ret - returns control back to the calling routine
• the call works by saving the address of where to return to when the function completes
• call - this is accomplished by placing contents of the RIP register on the stack
• the ret instruction pops the current top of the stack (RSP) into the RIP register (thus, the appropriate return address is restored)
• Argument Transmission - refers to sending information (variables, etc.) to a function and obtaining a result as appropriate for the specific function
• call-by-value - transmitting values to a function
• call-by-reference - transmitting addresses to a function is referred
• A combination of registers and stack is used to pass parameters to and/or from a function
• The first six integer arguments are passed in registers
• The seventh and any additional arguments are passed on the stack
• Arguments' registers:

  • rdi
  • rsi
  • rdx
  • rcx
  • r8
  • r9
• rax - where the return value is stored
• Preserved registers

  • rbx
  • rbp
  • r12
  • r13
  • r14
  • r15
• Temporary storage

  • r10
  • r11
• When the function is completed, the calling routine is responsible for clearing the arguments from the stack.
• For functions with return value, the result is placed in the A register based on the size of the value being returned.
• Call frame - the items on the stack as part of a function call
• Call frame - also referred to as an activation record or stack frame