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In
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, ...
, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instructions", as opposed to a data file that must be interpreted ( parsed) by a program to be meaningful. The exact interpretation depends upon the use. "Instructions" is traditionally taken to mean machine code instructions for a physical
CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, a ...
. In some contexts, a file containing scripting instructions (such as
bytecode Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (norma ...
) may also be considered executable.


Generation of executable files

Executable files can be hand-coded in machine language, although it is far more convenient to develop software as
source code In computing, source code, or simply code, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the ...
in a high-level language that can be easily understood by humans. In some cases, source code might be specified in
assembly language In computer programming, assembly language (or assembler language, or symbolic machine code), often referred to simply as Assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence b ...
instead, which remains human-readable while being closely associated with machine code instructions. The high-level language is
compiled In computing, a compiler is a computer program that translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primarily used for programs tha ...
into either an executable machine code file or a non-executable machine code – object file of some sort; the equivalent process on assembly language source code is called ''assembly''. Several object files are linked to create the executable. Object files -- executable or not -- are typically stored in a
container format A container format (informally, sometimes called a wrapper) or metafile is a file format that allows multiple data streams to be embedded into a single file, usually along with metadata for identifying and further detailing those streams. No ...
, such as
Executable and Linkable Format In computing, the Executable and Linkable FormatTool Interface Standard (TIS) Portable Formats SpecificationVersion 1.1'' (October 1993) (ELF, formerly named Extensible Linking Format), is a common standard file format for executable files, ...
(ELF) or Portable Executable (PE) which is
operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
-specific. This gives structure to the generated machine code, for example dividing it into sections such as
.text In computing, a code segment, also known as a text segment or simply as text, is a portion of an object file or the corresponding section of the program's virtual address space that contains executable instructions. Segment The term "segment" c ...
(executable code), .data (initialized global and static variables), and
.rodata In computing, a data segment (often denoted .data) is a portion of an object file or the corresponding address space of a program that contains initialized static variables, that is, global variables and static local variables. The size of this se ...
(read-only data, such as constants and strings). Executable files typically also include a runtime system, which implements runtime language features (such as task scheduling, exception handling, calling static constructors and destructors, etc.) and interactions with the operating system, notably passing arguments, environment, and returning an exit status, together with other startup and shutdown features such as releasing resources like file handles. For C, this is done by linking in the crt0 object, which contains the actual entry point and does setup and shutdown by calling the
runtime library In computer programming, a runtime library is a set of low-level routines used by a compiler to invoke some of the behaviors of a runtime environment, by inserting calls to the runtime library into compiled executable binary. The runtime enviro ...
. Executable files thus normally contain significant additional machine code beyond that directly generated from the specific source code. In some cases, it is desirable to omit this, for example for embedded systems development, or simply to understand how compilation, linking, and loading work. In C, this can be done by omitting the usual runtime, and instead explicitly specifying a linker script, which generates the entry point and handles startup and shutdown, such as calling main to start and returning exit status to the kernel at the end.


Execution

In order to be executed by the system (such as an operating system, firmware, or boot loader), an executable file must conform to the system's
application binary interface In computer software, an application binary interface (ABI) is an interface between two binary program modules. Often, one of these modules is a library or operating system facility, and the other is a program that is being run by a user. An ...
(ABI). In simple interfaces, a file is executed by loading it into memory and jumping to the start of the address space and executing from there. In more complicated interfaces, executable files have additional metadata specifying a separate entry point. For example, in ELF, the entry point is specified in the header's e_entry field, which specifies the (virtual) memory address at which to start execution. In the GCC (
GNU Compiler Collection The GNU Compiler Collection (GCC) is an optimizing compiler produced by the GNU Project supporting various programming languages, hardware architectures and operating systems. The Free Software Foundation (FSF) distributes GCC as free softwar ...
) this field is set by the linker based on the _start symbol.


See also

*
Comparison of executable file formats This is a comparison of binary executable file formats which, once loaded by a suitable executable loader, can be directly executed by the CPU rather than being interpreted by software. In addition to the binary application code, the executables ma ...
*
Executable compression Executable compression is any means of compressing an executable file and combining the compressed data with decompression code into a single executable. When this compressed executable is executed, the decompression code recreates the original ...
*
Executable text In hacking, a shellcode is a small piece of code used as the payload in the exploitation of a software vulnerability. It is called "shellcode" because it typically starts a command shell from which the attacker can control the compromised ma ...


References


External links


EXE File Format
at What Is {{Executables Computer file systems Programming language implementation