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At the level of code errors, this occurs when the program writes to part of its own code segment or the read-only portion of the data segment, as these are loaded by the OS into read-only memory. Here is an example of ANSI C code that will generally cause a segmentation fault on platforms with memory protection.
The C programming language manages memory statically, automatically, or dynamically.Static-duration variables are allocated in main memory, usually along with the executable code of the program, and persist for the lifetime of the program; automatic-duration variables are allocated on the stack and come and go as functions are called and return.
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.
Pointers in C programming Archived 2019-06-09 at the Wayback Machine A visual model for beginner C programmiers; 0pointer.de A terse list of minimum length source codes that dereference a null pointer in several different programming languages "The C book" – containing pointer examples in ANSI C
By way of comparison, on early segmented systems such as Burroughs MCP on the Burroughs B5000 (1961) and Multics (1964), and on paging systems such as IBM TSS/360 (1967) [c], code was also inherently position-independent, since subroutine virtual addresses in a program were located in private data external to the code, e.g., program reference ...
If however the program code dealing with segment 2 never uses offsets large enough to reach 0x77D0, then it can be thought of as a shorter, non-overlapping, and at most 30,672-byte segment. In real mode or V86 mode, the fundamental size of a segment is 65,536 bytes, with individual bytes being addressed using 16-bit offsets.
The correct number of sections for a fence is n − 1 if the fence is a free-standing line segment bounded by a post at each of its ends (e.g., a fence between two passageway gaps), n if the fence forms one complete, free-standing loop (e.g., enclosure accessible by surmounting, such as a boxing ring), or n + 1 if posts do not occur at the ends ...
For example, in an Intel 8086, as well as in later processors running 16-bit code, a far pointer has two parts: a 16-bit segment value, and a 16-bit offset value. A linear address is obtained by shifting the binary segment value four times to the left, and then adding the offset value. Hence the effective address is 21 bits [Note 1]. There can ...