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Segmentation faults can also occur independently of page faults: illegal access to a valid page is a segmentation fault, but not an invalid page fault, and segmentation faults can occur in the middle of a page (hence no page fault), for example in a buffer overflow that stays within a page but illegally overwrites memory.
Core dumps can save the context (state) of a process at a given state for returning to it later. Systems can be made highly available by transferring core between processors, sometimes via core dump files themselves. Core can also be dumped onto a remote host over a network (which is a security risk). [11]
On x86 there exists an older memory management mechanism known as segmentation. If the application loads a segment register with the selector of a non-present segment (which under POSIX-compliant OSes can only be done with assembly language), the exception is generated. Some OSes used that for swapping, but under Linux this generates SIGBUS.
The following is an excerpt from the Segfault story "Man clicks Internet banner ad": [3]. For the first time in recent memory, someone actually clicked an Internet banner ad.
The operating system delays loading parts of the program from disk until the program attempts to use it and the page fault is generated. If the page is not loaded in memory at the time of the fault, then it is called a major or hard page fault. The page fault handler in the OS needs to find a free location: either a free page in memory, or a ...
CS32 (Computational Thinking and Problem Solving), taught by Michael D. Smith, [29] is an alternative to CS50 but does not have a free online version. [30] The next course in sequence after CS32 or CS50 is CS51: Abstraction and Design in Computation, instructed by Stuart M. Shieber with Brian Yu as co-instructor. [31]
Instructions are always fetched from the code segment. Any stack push or pop or any data reference referring to the stack uses the stack segment. All other references to data use the data segment. The extra segment is the default destination for string operations (for example MOVS or CMPS). FS and GS have no hardware-assigned uses.
In a system using segmentation, computer memory addresses consist of a segment id and an offset within the segment. [3] A hardware memory management unit (MMU) is responsible for translating the segment and offset into a physical address, and for performing checks to make sure the translation can be done and that the reference to that segment and offset is permitted.