Explain the concept of a stack frame in a nutshell

Question

It seems that I get the idea of call stack in programming language design  But I cannot find  probably  I just don t search hard enough  any decent explanation of what stack frame is   So I would like to ask someone to explain it to me in a few words

User · Answer

A call stack is composed of stack frames           Wikipedia  A stack frame is a thing that you put on the stack  They are data structures that contain information about subroutines to call

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A stack frame is a frame of data that gets pushed onto the stack  In the case of a call stack  a stack frame would represent a function call and its argument data    If I remember correctly  the function return address is pushed onto the stack first  then the arguments and space for local variables  Together  they make the  frame   although this is likely architecture-dependent  The processor knows how many bytes are in each frame and moves the stack pointer accordingly as frames are pushed and popped off the stack   EDIT    There is a big difference between higher-level call stacks and the processor s call stack   When we talk about a processor s call stack  we are talking about working with addresses and values at the byte word level in assembly or machine code  There are  call stacks  when talking about higher-level languages  but they are a debugging runtime tool managed by the runtime environment so that you can log what went wrong with your program  at a high level   At this level  things like line numbers and method and class names are often known  By the time the processor gets the code  it has absolutely no concept of these things

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A quick wrap up  Maybe someone has a better explanation   A call stack is composed of 1 or many several stack frames  Each stack frame corresponds to a call to a function or procedure which has not yet terminated with a return    To use a stack frame  a thread keeps two pointers  one is called the Stack Pointer  SP   and the other is called the Frame Pointer  FP   SP always points to the  top  of the stack  and FP always points to the  top  of the frame  Additionally  the thread also maintains a program counter  PC  which points to the next instruction to be executed    The following are stored on the stack  local variables and temporaries  actual parameters of the current instruction  procedure  function  etc    There are different calling conventions regarding the cleaning of the stack

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Stack frame is the packed information related to a function call  This information generally includes arguments passed to th function  local variables and where to return upon terminating  Activation record is another name for a stack frame  The layout of the stack frame is determined in the ABI by the manufacturer and every compiler supporting the ISA must conform to this standard  however layout scheme can be compiler dependent  Generally stack frame size is not limited but there is a concept called  red protected zone  to allow system calls   etc to execute without interfering with a stack frame    There is always a SP but on some ABIs  ARM s and PowerPC s for example  FP is optional  Arguments that needed to be placed onto the stack can be offsetted using the SP only  Whether a stack frame is generated for a function call or not depends on the type and number of arguments  local variables and how local variables are accessed generally  On most ISAs  first  registers are used and if there are more arguments than registers dedicated to pass arguments these are placed onto the stack  For example x86 ABI has 6 registers to pass integer arguments   Hence  sometimes  some functions do not need a stack frame to be placed on the stack  just the return address is pushed onto the stack

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If you understand stack very well then you will understand how memory works in program and if you understand how memory works in program you will understand how function store in program and if you understand how function store in program you will understand how recursive function works and if you understand how recursive function works you will understand how compiler works and if you understand how compiler works your mind will works as compiler and you will debug any program very easily  Let me explain how stack works   First you have to know how functions are represented in stack    Heap stores dynamically allocated values  Stack stores automatic allocation and deletion values     Let s understand with example    def hello x       if x  1          return  op      else          u 1         e 12         s hello x-1          e  1         print s          print x          u  1     return e  hello 4    Now understand parts of this program      Now let s see what is stack and what are stack parts        Allocation of the stack     Remember one thing  if any function s return condition gets satisfied  no matter it has loaded the local variables or not  it will immediately return from stack with it s stack frame  It means that whenever any recursive function get base condition satisfied and we put a return after base condition  the base condition will not wait to load local variables which are located in the    else    part of program  It will immediately return the current frame from the stack following which the next frame is now in the activation record   See this in practice        Deallocation of the block    So now whenever a function encounters return statement  it delete the current frame from the stack   While returning from the stack  values will returned in reverse of the original order in which they were allocated in stack

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Programmers may have questions about stack frames not in a broad term  that it is a singe entity in the stack that serves just one function call and keeps return address  arguments and local variables  but in a narrow sense     when the term stack frames is mentioned in context of compiler options    Whether the author of the question has meant it or not  but the concept of a stack frame from the aspect of compiler options is a very important issue  not covered by the other replies here   For example  Microsoft Visual Studio 2015 C C   compiler has the following option related to stack frames     Oy   Frame-Pointer Omission    GCC have the following    -fomit-frame-pointer  Don t keep the frame pointer in a register for functions that don t need one  This avoids the instructions to save  set up and restore frame pointers  it also makes an extra register available in many functions    Intel C   Compiler have the following    -fomit-frame-pointer  Determines whether EBP is used as a general-purpose register in optimizations    which has the following alias     Oy   Delphi has the following command-line option    - W    Generate Stack Frames    In that specific sense  from the compiler   s perspective  a stack frame is just the entry and exit code for the routine  that pushes an anchor to the stack     that can also be used for debugging and for exception handling  Debugging tools may scan the stack data and use these anchors for backtracing  while locating call sites in the stack  i e  to display names of the functions in the order they have been called hierarchically  For Intel architecture  it is push ebp  mov ebp  esp or enter for entry and mov esp  ebp  pop ebp or leave for exit   That   s why it is very important to understand for a programmer what a stack frame is in when it comes to compiler options     because the compiler can control whether to generate this code or not   In some cases  the stack frame  entry and exit code for the routine  can be omitted by the compiler  and the variables will directly be accessed via the stack pointer  SP ESP RSP  rather than the convenient base pointer  BP ESP RSP   Conditions for omission of the stack frame  for example    the function is a leaf function  i e  an end-entity that doesn   t call other functions   there are no try finally or try except or similar constructs  i e  no exceptions are used  no routines are called with outgoing parameters on the stack  the function has no parameters  the function has no inline assembly code  etc      Omitting stack frames  entry and exit code for the routine  can make code smaller and faster  but it may also negatively affect the debuggers    ability to backtrace the data in the stack and to display it to the programmer  These are the compiler options that determine under which conditions a function should have the entry and exit code  for example   a  always   b  never   c  when needed  specifying the conditions

[callstack] Explain the concept of a stack frame in a nutshell

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