Stack overflow

Last updated

In software, a stack overflow occurs if the call stack pointer exceeds the stack bound. The call stack may consist of a limited amount of address space, often determined at the start of the program. The size of the call stack depends on many factors, including the programming language, machine architecture, multi-threading, and amount of available memory. When a program attempts to use more space than is available on the call stack (that is, when it attempts to access memory beyond the call stack's bounds, which is essentially a buffer overflow), the stack is said to overflow, typically resulting in a program crash. [1]

Contents

Causes

Infinite recursion

The most-common cause of stack overflow is excessively deep or infinite recursion, in which a function calls itself so many times that the space needed to store the variables and information associated with each call is more than can fit on the stack. [2]

An example of infinite recursion in C.

intfoo(){returnfoo();}

The function foo, when it is invoked, continues to invoke itself, allocating additional space on the stack each time, until the stack overflows resulting in a segmentation fault. [2] However, some compilers implement tail-call optimization, allowing infinite recursion of a specific sort—tail recursion—to occur without stack overflow. This works because tail-recursion calls do not take up additional stack space. [3]

Some C compiler options will effectively enable tail-call optimization; for example, compiling the above simple program using gcc with -O1 will result in a segmentation fault, but not when using -O2 or -O3, since these optimization levels imply the -foptimize-sibling-calls compiler option. [4] Other languages, such as Scheme, require all implementations to include tail-recursion as part of the language standard. [5]

Very deep recursion

A recursive function that terminates in theory but causes a call stack buffer overflow in practice can be fixed by transforming the recursion into a loop and storing the function arguments in an explicit stack (rather than the implicit use of the call stack). This is always possible because the class of primitive recursive functions is equivalent to the class of LOOP computable functions. Consider this example in C++-like pseudocode:

voidfunction(argument){if(condition)function(argument.next);}
stack.push(argument);while(!stack.empty()){argument=stack.pop();if(condition)stack.push(argument.next);}

A primitive recursive function like the one on the left side can always be transformed into a loop like on the right side.

A function like the example above on the left would not be a problem in an environment supporting tail-call optimization; however, it is still possible to create a recursive function that may result in a stack overflow in these languages. Consider the example below of two simple integer exponentiation functions.

intpow(intbase,intexp){if(exp>0)returnbase*pow(base,exp-1);elsereturn1;}
intpow(intbase,intexp){returnpow_accum(base,exp,1);}intpow_accum(intbase,intexp,intaccum){if(exp>0)returnpow_accum(base,exp-1,accum*base);elsereturnaccum;}

Both pow(base, exp) functions above compute an equivalent result, however, the one on the left is prone to causing a stack overflow because tail-call optimization is not possible for this function. During execution, the stack for these functions will look like this:

pow(5,4)5*pow(5,3)5*(5*pow(5,2))5*(5*(5*pow(5,1)))5*(5*(5*(5*pow(5,0))))5*(5*(5*(5*1)))625
pow(5,4)pow_accum(5,4,1)pow_accum(5,3,5)pow_accum(5,2,25)pow_accum(5,1,125)pow_accum(5,0,625)625

Notice that the function on the left must store in its stack exp number of integers, which will be multiplied when the recursion terminates and the function returns 1. In contrast, the function at the right must only store 3 integers at any time, and computes an intermediary result which is passed to its following invocation. As no other information outside of the current function invocation must be stored, a tail-recursion optimizer can "drop" the prior stack frames, eliminating the possibility of a stack overflow.

Very large stack variables

The other major cause of a stack overflow results from an attempt to allocate more memory on the stack than will fit, for example by creating local array variables that are too large. For this reason some authors recommend that arrays larger than a few kilobytes should be allocated dynamically instead of as a local variable. [6]

An example of a very large stack variable in C:

intfoo(){doublex[1048576];}

On a C implementation with 8 byte double-precision floats, the declared array consumes 8 megabytes of data; if this is more memory than is available on the stack (as set by thread creation parameters or operating system limits), a stack overflow will occur.

Stack overflows are made worse by anything that reduces the effective stack size of a given program. For example, the same program being run without multiple threads might work fine, but as soon as multi-threading is enabled the program will crash. This is because most programs with threads have less stack space per thread than a program with no threading support. Because kernels are generally multi-threaded, people new to kernel development are usually discouraged from using recursive algorithms or large stack buffers. [7]

See also

Related Research Articles

<span class="mw-page-title-main">Buffer overflow</span> Anomaly in computer security and programming

In programming and information security, a buffer overflow or buffer overrun is an anomaly whereby a program writes data to a buffer beyond the buffer's allocated memory, overwriting adjacent memory locations.

<span class="mw-page-title-main">Emacs Lisp</span> Dialect of Lisp used as an Emacs scripting language

Emacs Lisp is a dialect of the Lisp programming language used as a scripting language by Emacs. It is used for implementing most of the editing functionality built into Emacs, the remainder being written in C, as is the Lisp interpreter. Emacs Lisp is also termed Elisp, although there are also older, unrelated Lisp dialects with that name.

In mathematics and computer science, mutual recursion is a form of recursion where two mathematical or computational objects, such as functions or datatypes, are defined in terms of each other. Mutual recursion is very common in functional programming and in some problem domains, such as recursive descent parsers, where the datatypes are naturally mutually recursive.

In computing, a segmentation fault or access violation is a fault, or failure condition, raised by hardware with memory protection, notifying an operating system (OS) the software has attempted to access a restricted area of memory. On standard x86 computers, this is a form of general protection fault. The operating system kernel will, in response, usually perform some corrective action, generally passing the fault on to the offending process by sending the process a signal. Processes can in some cases install a custom signal handler, allowing them to recover on their own, but otherwise the OS default signal handler is used, generally causing abnormal termination of the process, and sometimes a core dump.

In computing, an optimizing compiler is a compiler that tries to minimize or maximize some attributes of an executable computer program. Common requirements are to minimize a program's execution time, memory footprint, storage size, and power consumption.

In computer science, divide and conquer is an algorithm design paradigm. A divide-and-conquer algorithm recursively breaks down a problem into two or more sub-problems of the same or related type, until these become simple enough to be solved directly. The solutions to the sub-problems are then combined to give a solution to the original problem.

C dynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely malloc, realloc, calloc, aligned_alloc and free.

<span class="mw-page-title-main">Pointer (computer programming)</span> Object which stores memory addresses in a computer program

In computer science, a pointer is an object in many programming languages that stores a memory address. This can be that of another value located in computer memory, or in some cases, that of memory-mapped computer hardware. A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlying computer architecture.

In computer programming, undefined behavior (UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres. This is different from unspecified behavior, for which the language specification does not prescribe a result, and implementation-defined behavior that defers to the documentation of another component of the platform.

Buffer overflow protection is any of various techniques used during software development to enhance the security of executable programs by detecting buffer overflows on stack-allocated variables, and preventing them from causing program misbehavior or from becoming serious security vulnerabilities. A stack buffer overflow occurs when a program writes to a memory address on the program's call stack outside of the intended data structure, which is usually a fixed-length buffer. Stack buffer overflow bugs are caused when a program writes more data to a buffer located on the stack than what is actually allocated for that buffer. This almost always results in corruption of adjacent data on the stack, which could lead to program crashes, incorrect operation, or security issues.

In computer programming, volatile means that a value is prone to change over time, outside the control of some code. Volatility has implications within function calling conventions, and also impacts how variables are stored, accessed and cached.

In computer science, a tail call is a subroutine call performed as the final action of a procedure. If the target of a tail is the same subroutine, the subroutine is said to be tail recursive, which is a special case of direct recursion. Tail recursion is particularly useful, and is often easy to optimize in implementations.

In computer programming, thread-local storage (TLS) is a memory management method that uses static or global memory local to a thread.

In computer science, a call stack is a stack data structure that stores information about the active subroutines of a computer program. This kind of stack is also known as an execution stack, program stack, control stack, run-time stack, or machine stack, and is often shortened to just "the stack". Although maintenance of the call stack is important for the proper functioning of most software, the details are normally hidden and automatic in high-level programming languages. Many computer instruction sets provide special instructions for manipulating stacks.

<span class="mw-page-title-main">Recursion (computer science)</span> Use of functions that call themselves

In computer science, recursion is a method of solving a computational problem where the solution depends on solutions to smaller instances of the same problem. Recursion solves such recursive problems by using functions that call themselves from within their own code. The approach can be applied to many types of problems, and recursion is one of the central ideas of computer science.

The power of recursion evidently lies in the possibility of defining an infinite set of objects by a finite statement. In the same manner, an infinite number of computations can be described by a finite recursive program, even if this program contains no explicit repetitions.

In compiler optimization, escape analysis is a method for determining the dynamic scope of pointers – where in the program a pointer can be accessed. It is related to pointer analysis and shape analysis.

In software, a stack buffer overflow or stack buffer overrun occurs when a program writes to a memory address on the program's call stack outside of the intended data structure, which is usually a fixed-length buffer. Stack buffer overflow bugs are caused when a program writes more data to a buffer located on the stack than what is actually allocated for that buffer. This almost always results in corruption of adjacent data on the stack, and in cases where the overflow was triggered by mistake, will often cause the program to crash or operate incorrectly. Stack buffer overflow is a type of the more general programming malfunction known as buffer overflow. Overfilling a buffer on the stack is more likely to derail program execution than overfilling a buffer on the heap because the stack contains the return addresses for all active function calls.

<span class="mw-page-title-main">Secure coding</span> Software development methodology

Secure coding is the practice of developing computer software in such a way that guards against the accidental introduction of security vulnerabilities. Defects, bugs and logic flaws are consistently the primary cause of commonly exploited software vulnerabilities. Through the analysis of thousands of reported vulnerabilities, security professionals have discovered that most vulnerabilities stem from a relatively small number of common software programming errors. By identifying the insecure coding practices that lead to these errors and educating developers on secure alternatives, organizations can take proactive steps to help significantly reduce or eliminate vulnerabilities in software before deployment.

In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed.

A code sanitizer is a programming tool that detects bugs in the form of undefined or suspicious behavior by a compiler inserting instrumentation code at runtime. The class of tools was first introduced by Google's AddressSanitizer of 2012, which uses directly mapped shadow memory to detect memory corruption such as buffer overflows or accesses to a dangling pointer (use-after-free).

References

  1. ↑ Burley, James Craig (1991-06-01). "Using and Porting GNU Fortran". Archived from the original on 2012-02-06.
  2. 1 2 What is the difference between a segmentation fault and a stack overflow? Archived 2021-09-13 at the Wayback Machine at Stack Overflow
  3. ↑ "An Introduction to Scheme and its Implementation". 1997-02-19. Archived from the original on 2007-08-10.
  4. ↑ "Using the GNU Compiler Collection (GCC): Optimize Options". Archived from the original on 2017-08-20. Retrieved 2017-08-20.
  5. ↑ Richard Kelsey; William Clinger; Jonathan Rees; et al. (August 1998). "Revised5 Report on the Algorithmic Language Scheme". Higher-Order and Symbolic Computation. 11 (1): 7–105. doi:10.1023/A:1010051815785. S2CID   14069423. Archived from the original on 2007-01-05. Retrieved 2012-08-09.
  6. ↑ Feldman, Howard (2005-11-23). "Modern Memory Management, Part 2". Archived from the original on 2012-09-20. Retrieved 2007-08-14.
  7. ↑ "Kernel Programming Guide: Performance and Stability Tips". Apple Inc. 2014-05-02. Archived from the original on 2014-05-03. Retrieved 2014-05-02.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.