SIGSEGV
Encyclopedia
On POSIX
-compliant platforms,
when it makes an invalid memory reference, or segmentation fault
. The symbolic constant
for
of segmentation violation.
). The operating system
may inform the application of the nature of the error using the signal stack
, which developers can use to debug their programs or handle errors.
The default action for a program upon receiving
, but may generate a core file to aid debugging, or perform some other platform-dependent action. For example, Linux
systems using the grsecurity
patch may log
s.
, or restoring the default action. In some circumstances, ignoring
An example of an application that might handle
, which might check the signal stack and inform the developer
of what happened, and where the program terminated.
, but users with appropriate permissions can use the
or kill
command (a userland program, or sometimes a shell
builtin) to send the signal to a process at will.
POSIX
POSIX , an acronym for "Portable Operating System Interface", is a family of standards specified by the IEEE for maintaining compatibility between operating systems...
-compliant platforms,
SIGSEGV is the signal sent to a processProcess (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
when it makes an invalid memory reference, or segmentation fault
Segmentation fault
A segmentation fault , bus error or access violation is generally an attempt to access memory that the CPU cannot physically address. It occurs when the hardware notifies an operating system about a memory access violation. The OS kernel then sends a signal to the process which caused the exception...
. The symbolic constant
C preprocessor
The C preprocessor is the preprocessor for the C and C++ computer programming languages. The preprocessor handles directives for source file inclusion , macro definitions , and conditional inclusion ....
for
SIGSEGV is defined in the header fileHeader file
Some programming languages use header files. These files allow programmers to separate certain elements of a program's source code into reusable files. Header files commonly contain forward declarations of classes, subroutines, variables, and other identifiers...
signal.hSignal.hsignal.h is a header file defined in the C Standard Library to specify how a program handles signals while it executes. A signal can report some exceptional behavior within the program , or a signal can report some asynchronous event outside the program .A signal can be generated...
. Symbolic signal names are used because signal numbers can vary across platforms; in practice it is usually signal number 11.Etymology
SIG is a common prefix for signal names; SEGV is an abbreviationAbbreviation
An abbreviation is a shortened form of a word or phrase. Usually, but not always, it consists of a letter or group of letters taken from the word or phrase...
of segmentation violation.
Usage
Computer programs may throwSIGSEGV for improper memory handling (see segmentation faultSegmentation fault
A segmentation fault , bus error or access violation is generally an attempt to access memory that the CPU cannot physically address. It occurs when the hardware notifies an operating system about a memory access violation. The OS kernel then sends a signal to the process which caused the exception...
). The operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
may inform the application of the nature of the error using the signal stack
Stack (data structure)
In computer science, a stack is a last in, first out abstract data type and linear data structure. A stack can have any abstract data type as an element, but is characterized by only three fundamental operations: push, pop and stack top. The push operation adds a new item to the top of the stack,...
, which developers can use to debug their programs or handle errors.
The default action for a program upon receiving
SIGSEGV is abnormal termination. This action will end the processProcess (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
, but may generate a core file to aid debugging, or perform some other platform-dependent action. For example, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
systems using the grsecurity
Grsecurity
grsecurity is a set of patches for the Linux kernel with an emphasis on enhancing security. Its typical application is in computer systems that accept remote connections from untrusted locations, such as web servers and systems offering shell access to its users.Released under the GNU General...
patch may log
SIGSEGV signals in order to monitor for possible intrusion attempts using buffer overflowBuffer overflow
In computer security and programming, a buffer overflow, or buffer overrun, is an anomaly where a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory. This is a special case of violation of memory safety....
s.
SIGSEGV can be caught; that is, applications can request what action they want to occur in place of the default. Examples of such action might be ignoring it, calling a functionSubroutine
In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....
, or restoring the default action. In some circumstances, ignoring
SIGSEGV results in undefined behavior.An example of an application that might handle
SIGSEGV is a debuggerDebugger
A debugger or debugging tool is a computer program that is used to test and debug other programs . The code to be examined might alternatively be running on an instruction set simulator , a technique that allows great power in its ability to halt when specific conditions are encountered but which...
, which might check the signal stack and inform the developer
Software developer
A software developer is a person concerned with facets of the software development process. Their work includes researching, designing, developing, and testing software. A software developer may take part in design, computer programming, or software project management...
of what happened, and where the program terminated.
SIGSEGV is usually generated by the operating systemOperating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
, but users with appropriate permissions can use the
kill system callSystem call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
or kill
Kill (Unix)
In computing, kill is a command that is used in several popular operating systems to send signals to running processes, for example to request the termination of this process.-Unix and Unix-like:...
command (a userland program, or sometimes a shell
Shell (computing)
A shell is a piece of software that provides an interface for users of an operating system which provides access to the services of a kernel. However, the term is also applied very loosely to applications and may include any software that is "built around" a particular component, such as web...
builtin) to send the signal to a process at will.
AIX
In the AIX operating system, for 32-bit executables,SIGSEGV can be generated due to insufficient segment-size. The way the memory model of AIX is designed, segments, by default, have a fixed size (256Mb). In case a process requests more memory than this, a segment violation occurs and the operating system delivers a SIGSEGV signal to the process. For resolving this, one can link with -bmaxdata= or set the runtime environment variable LDR_CNTRL=MAXDATA.