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Prebinding
In computing, prebinding, also called prelinking, is a method for optimizing application load times by resolving library symbols prior to launch. Background Most computer programs consist of code that requires external shared libraries to execute. These libraries are normally integrated with the program at run time by a loader, in a process called dynamic linking. While dynamic linking has advantages in code size and management, there are drawbacks as well. Every time a program is run, the loader needs to resolve (find) the relevant libraries. Since libraries move around in memory, there is a performance penalty for resolution. This penalty increases for each additional library needing resolution. Prelinking reduces this penalty by resolving libraries in advance. Afterward, resolution only occurs if the libraries have changed since being prelinked, such as following perhaps an upgrade. Mac OS Mac OS stores executables in the Mach-O file format. Mac OS X Mac OS X performs ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shared Library
In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subroutines, classes, values or type specifications. In IBM's OS/360 and its successors they are referred to as partitioned data sets. A library is also a collection of implementations of behavior, written in terms of a language, that has a well-defined interface by which the behavior is invoked. For instance, people who want to write a higher-level program can use a library to make system calls instead of implementing those system calls over and over again. In addition, the behavior is provided for reuse by multiple independent programs. A program invokes the library-provided behavior via a mechanism of the language. For example, in a simple imperative language such as C, the behavior in a library is invoked by using C's normal functio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Library (computing)
In computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and subroutines, classes, values or type specifications. In IBM's OS/360 and its successors they are referred to as partitioned data sets. A library is also a collection of implementations of behavior, written in terms of a language, that has a well-defined interface by which the behavior is invoked. For instance, people who want to write a higher-level program can use a library to make system calls instead of implementing those system calls over and over again. In addition, the behavior is provided for reuse by multiple independent programs. A program invokes the library-provided behavior via a mechanism of the language. For example, in a simple imperative language such as C, the behavior in a library is invoked by using C's normal functi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Linker (computing)
In computing, a linker or link editor is a computer system program that takes one or more object files (generated by a compiler or an assembler) and combines them into a single executable file, library file, or another "object" file. A simpler version that writes its output directly to memory is called the ''loader'', though loading is typically considered a separate process. Overview Computer programs typically are composed of several parts or modules; these parts/modules do not need to be contained within a single object file, and in such cases refer to each other by means of symbols as addresses into other modules, which are mapped into memory addresses when linked for execution. While the process of linking is meant to ultimately combine these independent parts, there are many good reasons to develop those separately at the source-level. Among these reasons are the ease of organizing several smaller pieces over a monolithic whole and the ability to better define ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, engineering, mathematical, technological and social aspects. Major computing disciplines include computer engineering, computer science, cybersecurity, data science, information systems, information technology and software engineering. The term "computing" is also synonymous with counting and calculating. In earlier times, it was used in reference to the action performed by mechanical computing machines, and before that, to human computers. History The history of computing is longer than the history of computing hardware and includes the history of methods intended for pen and paper (or for chalk and slate) with or without the aid of tables. Computing is intimately tied to the representation of numbers, though mathematical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Address Space Layout Randomization
Address space layout randomization (ASLR) is a computer security technique involved in preventing exploitation of memory corruption vulnerabilities. In order to prevent an attacker from reliably jumping to, for example, a particular exploited function in memory, ASLR randomly arranges the address space positions of key data areas of a process, including the base of the executable and the positions of the stack, heap and libraries. History The Linux PaX project first coined the term "ASLR", and published the first design and implementation of ASLR in July 2001 as a patch for the Linux kernel. It is seen as a complete implementation, providing also a patch for kernel stack randomization since October 2002. The first mainstream operating system to support ASLR by default was OpenBSD version 3.4 in 2003, followed by Linux in 2005. Benefits Address space randomization hinders some types of security attacks by making it more difficult for an attacker to predict target ad ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Object File
An object file is a computer file containing object code, that is, machine code output of an assembler or compiler. The object code is usually relocatable, and not usually directly executable. There are various formats for object files, and the same machine code can be packaged in different object file formats. An object file may also work like a shared library. In addition to the object code itself, object files may contain metadata used for linking or debugging, including: information to resolve symbolic cross-references between different modules, relocation information, stack unwinding information, comments, program symbols, debugging or profiling information. Other metadata may include the date and time of compilation, the compiler name and version, and other identifying information. The term "object program" dates from at least the 1950s: A computer programmer generates object code with a compiler or assembler. For example, under Linux, the GNU Compiler Collection ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dynamic Binding (computer Science)
In computing, late binding or dynamic linkage—though not an identical process to dynamically linking imported code libraries—is a computer programming mechanism in which the method being called upon an object, or the function being called with arguments, is looked up by name at runtime. In other words, a name is associated with a particular operation or object at runtime, rather than during compilation. The name dynamic binding is sometimes used, but is more commonly used to refer to dynamic scope. With early binding, or static binding, in an object-oriented language, the compilation phase fixes all types of variables and expressions. This is usually stored in the compiled program as an offset in a virtual method table ("v-table"). In contrast, with late binding, the compiler does not read enough information to verify the method exists or bind its slot on the v-table. Instead, the method is looked up by name at runtime. The primary advantage of using late binding in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Segfault
In computing, a segmentation fault (often shortened to segfault) 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 (a memory access violation). 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,''Expert C programming: deep C secrets'' By Peter Van der Linden, page 188 but otherwise the OS default signal handler is used, generally causing abnormal termination of the process (a program crash), and sometimes a core dump. Segmentation faults are a common class of error in programs written in languages like C that provide low-level memory access an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OpenMPI
Open MPI is a Message Passing Interface (MPI) library project combining technologies and resources from several other projects (FT-MPI, LA-MPI, LAM/MPI, and PACX-MPI). It is used by many TOP500 supercomputers including Roadrunner, which was the world's fastest supercomputer from June 2008 to November 2009, and K computer, the fastest supercomputer from June 2011 to June 2012. Overview Open MPI represents the merger between three well-known MPI implementations: * FT-MPI from the University of Tennessee * LA-MPI from Los Alamos National Laboratory * LAM/MPI from Indiana University with contributions from the PACX-MPI team at the University of Stuttgart. These four institutions comprise the founding members of the Open MPI development team. The Open MPI developers selected these MPI implementations as excelling in one or more areas. Open MPI aims to use the best ideas and technologies from the individual projects and create one world-class open-source MPI implementation th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Application Checkpoint
Checkpointing is a technique that provides fault tolerance for computing systems. It basically consists of saving a snapshot of the application's state, so that applications can restart from that point in case of failure. This is particularly important for long running applications that are executed in failure-prone computing systems. Checkpointing in distributed systems In the distributed computing environment, checkpointing is a technique that helps tolerate failures that otherwise would force long-running application to restart from the beginning. The most basic way to implement checkpointing, is to stop the application, copy all the required data from the memory to reliable storage (e.g., parallel file system) and then continue with the execution. In case of failure, when the application restarts, it does not need to start from scratch. Rather, it will read the latest state ("the checkpoint") from the stable storage and execute from that. While there is ongoing debate on w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SUID
The Unix access rights flags setuid and setgid (short for ''set user identity'' and ''set group identity'') allow users to run an executable with the file system permissions of the executable's owner or group respectively and to change behaviour in directories. They are often used to allow users on a computer system to run programs with temporarily elevated privileges in order to perform a specific task. While the assumed user id or group id privileges provided are not always elevated, at a minimum they are specific. The flags setuid and setgid are needed for tasks that require different privileges than what the user is normally granted, such as the ability to alter system files or databases to change their login password. Some of the tasks that require additional privileges may not immediately be obvious, though, such as the ping command, which must send and listen for control packets on a network interface. File modes The setuid and setgid bits are normally represented as t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
