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56-554: The source code, including the just-in-time compiler and conservative garbage collector , was donated to the Mozilla Foundation on November 7, 2006. The contributed code is tri-licensed under the GPL , LGPL , and MPL licenses to be developed in Mozilla's Mercurial repository. The contributed code is approximately 135,000 lines of code, making it the largest single donation of code to

112-431: A monolithic whole and the ability to better define the purpose and responsibilities of each individual piece, which is essential for managing complexity and increasing long-term maintainability in software architecture . Typically, an object file can contain three kinds of symbols: For most compilers, each object file is the result of compiling one input source code file. When a program comprises multiple object files,

168-427: A shared library , the entire library has to be loaded during runtime as it is not known which functions or methods will be called during runtime. Library linking may thus be an iterative process, with some referenced modules requiring additional modules to be linked, and so on. Libraries exist for diverse purposes, and one or more system libraries are usually linked in by default. The linker also takes care of arranging

224-556: A JIT must render and execute a native binary image at runtime, true machine-code JITs necessitate platforms that allow for data to be executed at runtime, making using such JITs on a Harvard architecture -based machine impossible; the same can be said for certain operating systems and virtual machines as well. However, a special type of "JIT" may potentially not target the physical machine's CPU architecture, but rather an optimized VM bytecode where limitations on raw machine code prevail, especially where that bytecode's VM eventually leverages

280-402: A JIT to native code. JIT causes a slight to noticeable delay in the initial execution of an application, due to the time taken to load and compile the input code. Sometimes this delay is called "startup time delay" or "warm-up time". In general, the more optimization JIT performs, the better the code it will generate, but the initial delay will also increase. A JIT compiler therefore has to make

336-401: A few routines from a library does not require the entire library to be installed. As the compiler has no information on the layout of objects in the final output, it cannot take advantage of shorter or more efficient instructions that place a requirement on the address of another object. For example, a jump instruction can reference an absolute address or an offset from the current location, and

392-405: A linker (assembling object files into a program) was called loading (as in loading executable code onto a file). Additionally, in some operating systems, the same program handles both the jobs of linking and loading a program ( dynamic linking ). Many operating system environments allow dynamic linking, deferring the resolution of some undefined symbols until a program is run. That means that

448-504: A result, no runtime compilation is needed. .NET Framework 2.0 shipped with Visual Studio 2005 runs Ngen on all of the Microsoft library DLLs right after the installation. Pre-jitting provides a way to improve the startup time. However, the quality of code it generates might not be as good as the one that is JITed, for the same reasons why code compiled statically, without profile-guided optimization , cannot be as good as JIT compiled code in

504-417: A single object file , and in such cases refer to each other using 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

560-448: A single process execution. On Linux , they found that 8.7% to 9.6% of process executions failed to reach a steady state of performance, 16.7% to 17.9% entered a steady state of reduced performance after a warmup period, and 56.5% pairings of a specific virtual machine running a specific benchmark failed to consistently see a steady-state non-degradation of performance across multiple executions (i.e., at least one execution failed to reach

616-474: A software project. A linker script may be passed to GNU ld to exercise greater control over the linking process. The GNU linker is part of the GNU Binary Utilities (binutils). Two versions of ld are provided in binutils: the traditional GNU ld based on bfd , and a "streamlined" ELF-only version called gold . The command-line and linker script syntaxes of GNU ld is the de facto standard in much of

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672-505: A steady state across multiple executions. JIT compilation fundamentally uses executable data, and thus poses security challenges and possible exploits. Implementation of JIT compilation consists of compiling source code or byte code to machine code and executing it. This is generally done directly in memory: the JIT compiler outputs the machine code directly into memory and immediately executes it, rather than outputting it to disk and then invoking

728-464: A steady state or saw reduced performance in the steady state). Even where an improved steady-state was reached, it sometimes took many hundreds of iterations. Traini et al. (2022) instead focused on the HotSpot virtual machine but with a much wider array of benchmarks, finding that 10.9% of process executions failed to reach a steady state of performance, and 43.5% of benchmarks did not consistently attain

784-506: A text editor may compile a regular expression provided at runtime to machine code to allow faster matching: this cannot be done ahead of time, as the pattern is only provided at runtime. Several modern runtime environments rely on JIT compilation for high-speed code execution, including most implementations of Java , together with Microsoft 's .NET . Similarly, many regular-expression libraries feature JIT compilation of regular expressions, either to bytecode or to machine code. JIT compilation

840-517: A trade-off between the compilation time and the quality of the code it hopes to generate. Startup time can include increased IO-bound operations in addition to JIT compilation: for example, the rt.jar class data file for the Java Virtual Machine (JVM) is 40 MB and the JVM must seek a lot of data in this contextually huge file. One possible optimization, used by Sun's HotSpot Java Virtual Machine,

896-456: Is compilation (of computer code ) during execution of a program (at run time ) rather than before execution. This may consist of source code translation but is more commonly bytecode translation to machine code , which is then executed directly. A system implementing a JIT compiler typically continuously analyses the code being executed and identifies parts of the code where the speedup gained from compilation or recompilation would outweigh

952-487: 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. Computer programs typically are composed of several parts or modules; these parts/modules do not need to be contained within

1008-625: Is a form of dynamic compilation , and allows adaptive optimization such as dynamic recompilation and microarchitecture -specific speedups. Interpretation and JIT compilation are particularly suited for dynamic programming languages , as the runtime system can handle late-bound data types and enforce security guarantees. The earliest published JIT compiler is generally attributed to work on LISP by John McCarthy in 1960. In his seminal paper Recursive functions of symbolic expressions and their computation by machine, Part I , he mentions functions that are translated during runtime, thereby sparing

1064-527: Is a security hole (see W^X ). For instance Firefox's JIT compiler for Javascript introduced this protection in a release version with Firefox 46. JIT spraying is a class of computer security exploits that use JIT compilation for heap spraying : the resulting memory is then executable, which allows an exploit if execution can be moved into the heap. JIT compilation can be applied to some programs, or can be used for certain capacities, particularly dynamic capacities such as regular expressions . For example,

1120-435: Is also used in some emulators, in order to translate machine code from one CPU architecture to another. A common implementation of JIT compilation is to first have AOT compilation to bytecode ( virtual machine code), known as bytecode compilation , and then have JIT compilation to machine code (dynamic compilation), rather than interpretation of the bytecode. This improves the runtime performance compared to interpretation, at

1176-485: Is compiled prior to deployment. A dynamic compilation environment is one in which the compiler can be used during execution. A common goal of using JIT techniques is to reach or surpass the performance of static compilation , while maintaining the advantages of bytecode interpretation: Much of the "heavy lifting" of parsing the original source code and performing basic optimization is often handled at compile time, prior to deployment: compilation from bytecode to machine code

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1232-417: Is finally loaded into memory (just before execution). This pass is usually omitted on hardware offering virtual memory : every program is put into its own address space, so there is no conflict even if all programs load at the same base address. This pass may also be omitted if the executable is a position independent executable. On some Unix variants, such as SINTRAN III , the process performed by

1288-468: Is in the form and format of 80-byte punched-card images, so that updates can be introduced into a system using that medium. In later releases of OS/360 and in subsequent systems, load-modules contain additional data about versions of components modules, to create a traceable record of updates. It also allows one to add, change, or remove an overlay structure from an already linked load module. The term "linkage editor" should not be construed as implying that

1344-422: Is led by Mark Hammond. Neither project had production-quality releases and their current status is unclear. Both SpiderMonkey and Tamarin fulfill closely related goals and so were given names derived from types of monkeys (the spider monkey and the tamarin , respectively). Just-in-time compiler In computing , just-in-time ( JIT ) compilation (also dynamic translation or run-time compilations )

1400-562: Is much faster than compiling from source. The deployed bytecode is portable, unlike native code. Since the runtime has control over the compilation, like interpreted bytecode, it can run in a secure sandbox. Compilers from bytecode to machine code are easier to write, because the portable bytecode compiler has already done much of the work. JIT code generally offers far better performance than interpreters. In addition, it can in some cases offer better performance than static compilation, as many optimizations are only feasible at run-time: Because

1456-410: Is not the machine code for any particular computer, and may be portable among computer architectures. The bytecode may then be interpreted by, or run on a virtual machine . The JIT compiler reads the bytecodes in many sections (or in full, rarely) and compiles them dynamically into machine code so the program can run faster. This can be done per-file, per-function or even on any arbitrary code fragment;

1512-507: Is only a part of Flash Player. Two projects related to Tamarin were announced on July 25, 2007, in Brendan Eich 's keynote at The Ajax Experience West: IronMonkey and ScreamingMonkey. IronMonkey is a project to map IronPython and IronRuby to Tamarin led by Seo Sanghyeon. ScreamingMonkey's goal is to allow Tamarin to run within non-Mozilla browsers (thus allowing them to understand JavaScript 2), starting with Internet Explorer . The project

1568-409: Is performed, to reduce startup time. In server mode, extensive compilation and optimization is performed, to maximize performance once the application is running by sacrificing startup time. Other Java just-in-time compilers have used a runtime measurement of the number of times a method has executed combined with the bytecode size of a method as a heuristic to decide when to compile. Still another uses

1624-463: Is the result of the linker copying all library routines used in the program into the executable image. This may require more disk space and memory than dynamic linking, but is more portable, since it does not require the presence of the library on the system where it runs. Static linking also prevents "DLL hell", since each program includes exactly the versions of library routines that it requires, with no conflict with other programs. A program using just

1680-409: Is to combine interpretation and JIT compilation. The application code is initially interpreted, but the JVM monitors which sequences of bytecode are frequently executed and translates them to machine code for direct execution on the hardware. For bytecode which is executed only a few times, this saves the compilation time and reduces the initial latency; for frequently executed bytecode, JIT compilation

1736-415: Is used by most implementations of the Java Virtual Machine , as HotSpot builds on, and extensively uses, this research base. The HP project Dynamo was an experimental JIT compiler where the "bytecode" format and the machine code format were the same; the system optimized PA-8000 machine code. Counterintuitively, this resulted in speed ups, in some cases of 30% since doing this permitted optimizations at

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1792-457: Is used to generate native code when performing just-in-time compilation . Adobe contributed code for its ActionScript Virtual Machine 2 and the JIT compiler. The ActionScript compiler is also open source as a part of Adobe Flex . There is also CrossBridge , an open source C and C++ compiler. Tamarin is not the same as Adobe Flash Player , which remains closed source. The Tamarin virtual machine

1848-540: Is used to run at high speed, after an initial phase of slow interpretation. Additionally, since a program spends most time executing a minority of its code, the reduced compilation time is significant. Finally, during the initial code interpretation, execution statistics can be collected before compilation, which helps to perform better optimization. The correct tradeoff can vary due to circumstances. For example, Sun's Java Virtual Machine has two major modes—client and server. In client mode, minimal compilation and optimization

1904-506: The linker relaxation pass subsequently reassigns addresses, which may in turn allow more potential relaxations to occur. In general, the substituted sequences are shorter, which allows this process to always converge on the best solution given a fixed order of objects; if this is not the case, relaxations can conflict, and the linker needs to weigh the advantages of either option. While instruction relaxation typically occurs at link-time, inner-module relaxation can already take place as part of

1960-460: The Mozilla project besides Netscape itself. There were plans to use Tamarin as part of Mozilla 2 (and therefore Firefox 4). The project to integrate Tamarin and SpiderMonkey was called "ActionMonkey", but was canceled in 2008 because Tamarin's interpreter turned out to be slower than SpiderMonkey's and because the plans of ECMAScript development shifted from ECMAScript 4 , which was partially implemented by then existing Tamarin source code and

2016-423: The additional capability of allowing the addition, replacement, and/or deletion of individual program sections. Operating systems such as OS/360 have format for executable load-modules containing supplementary data about the component sections of a program, so that an individual program section can be replaced, and other parts of the program updated so that relocatable addresses and other references can be corrected by

2072-423: The code as a separate program, as in usual ahead of time compilation. In modern architectures this runs into a problem due to executable space protection : arbitrary memory cannot be executed, as otherwise there is a potential security hole. Thus memory must be marked as executable; for security reasons this should be done after the code has been written to memory, and marked read-only, as writable/executable memory

2128-459: The code can be compiled when it is about to be executed (hence the name "just-in-time"), and then cached and reused later without needing to be recompiled. By contrast, a traditional interpreted virtual machine will simply interpret the bytecode, generally with much lower performance. Some interpreter s even interpret source code, without the step of first compiling to bytecode, with even worse performance. Statically-compiled code or native code

2184-408: The cost of lag due to compilation. JIT compilers translate continuously, as with interpreters, but caching of compiled code minimizes lag on future execution of the same code during a given run. Since only part of the program is compiled, there is significantly less lag than if the entire program were compiled prior to execution. Linker (computing) In computing , a linker or link editor

2240-449: The executable code still contains undefined symbols, plus a list of objects or libraries that will provide definitions for these. Loading the program will load these objects/libraries as well, and perform a final linking. This approach offers two advantages: There are also disadvantages: Contained or virtual environments may further allow system administrators to mitigate or trade-off these individual pros and cons. Static linking

2296-626: The extreme case: the lack of profiling data to drive, for instance, inline caching. There also exist Java implementations that combine an AOT (ahead-of-time) compiler with either a JIT compiler ( Excelsior JET ) or interpreter ( GNU Compiler for Java ). JIT compilation may not reliably achieve its goal, namely entering a steady state of improved performance after a short initial warmup period. Across eight different virtual machines, Barrett et al. (2017) measured six widely-used microbenchmarks which are commonly used by virtual machine implementors as optimisation targets, running them repeatedly within

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2352-427: The linkage editor, as part of the process. One advantage of this is that it allows a program to be maintained without having to keep all of the intermediate object files, or without having to re-compile program sections that haven't changed. It also permits program updates to be distributed in the form of small files (originally card decks ), containing only the object module to be replaced. In such systems, object code

2408-430: The linker combines these files into a unified executable program, resolving the symbols as it goes along. Linkers can take objects from a collection called a library or runtime library . Most linkers do not include all the object files in a static library in the output executable; they include only those object files from the library that are referenced by other object files or libraries directly or indirectly. But for

2464-543: The linker is known as "ld". Origins of the name "ld" are "LoaDer" and "Link eDitor". The term "loader" was used to describe the process of loading external symbols from other programs during the process of linking. The GNU linker (or GNU ld) is the GNU Project 's free software implementation of the Unix command ld. GNU ld runs the linker, which creates an executable file (or a library) from object files created during compilation of

2520-469: The machine code level, for example, inlining code for better cache usage and optimizations of calls to dynamic libraries and many other run-time optimizations which conventional compilers are not able to attempt. In November 2020, PHP 8.0 introduced a JIT compiler. In October 2024, CPython introduced an experimental JIT compiler. In a bytecode-compiled system, source code is translated to an intermediate representation known as bytecode . Bytecode

2576-581: The need to save the compiler output to punch cards (although this would be more accurately known as a " Compile and go system "). Another early example was by Ken Thompson , who in 1968 gave one of the first applications of regular expressions , here for pattern matching in the text editor QED . For speed, Thompson implemented regular expression matching by JITing to IBM 7094 code on the Compatible Time-Sharing System . An influential technique for deriving compiled code from interpretation

2632-418: The number of times executed combined with the detection of loops. In general, it is much harder to accurately predict which methods to optimize in short-running applications than in long-running ones. Native Image Generator (Ngen) by Microsoft is another approach at reducing the initial delay. Ngen pre-compiles (or "pre-JITs") bytecode in a Common Intermediate Language image into machine native code. As

2688-420: The objects in a program's address space . This may involve relocating code that assumes a specific base address into another base. Since a compiler seldom knows where an object will reside, it often assumes a fixed base location (for example, zero ). Relocating machine code may involve re-targeting absolute jumps, loads, and stores. The executable output by the linker may need another relocation pass when it

2744-526: The offset could be expressed with different lengths depending on the distance to the target. By first generating the most conservative instruction (usually the largest relative or absolute variant, depending on platform) and adding relaxation hints , it is possible to substitute shorter or more efficient instructions during the final link. In regard to jump optimizations this is also called automatic jump-sizing . This step can be performed only after all input objects have been read and assigned temporary addresses;

2800-407: The optimizing process at compile-time . In some cases, relaxation can also occur at load-time as part of the relocation process or combined with dynamic dead-code elimination techniques. In IBM System/360 mainframe environments such as OS/360 , including z/OS for the z/Architecture mainframes, this type of program is known as a linkage editor . As the name implies a linkage editor has

2856-490: The overhead of compiling that code. JIT compilation is a combination of the two traditional approaches to translation to machine code— ahead-of-time compilation (AOT) , and interpretation —and combines some advantages and drawbacks of both. Roughly, JIT compilation combines the speed of compiled code with the flexibility of interpretation, with the overhead of an interpreter and the additional overhead of compiling and linking (not just interpreting). JIT compilation

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2912-414: The program operates in a user-interactive mode like a text editor. It is intended for batch-mode execution, with the editing commands being supplied by the user in sequentially organized files, such as punched cards , DASD , or magnetic tape . Linkage editing ( IBM nomenclature) or consolidation or collection ( ICL nomenclature) refers to the linkage editor's or consolidator's act of combining

2968-609: The various pieces into a relocatable binary, whereas the loading and relocation into an absolute binary at the target address is normally considered a separate step. In the beginning linkers gave users very limited control over the arrangement of generated output object files. As the target systems became complex with different memory requirements such as embedded systems, it became necessary to give users control to generate output object files with their specific requirements such as defining base addresses' of segments. Linkers control scripts were used for this. On Unix and Unix-like systems,

3024-453: Was at one point the fastest Smalltalk system in the world, achieving up to half the speed of optimized C but with a fully object-oriented language. Self was abandoned by Sun, but the research went into the Java language. The term "Just-in-time compilation" was borrowed from the manufacturing term " Just in time " and popularized by Java, with James Gosling using the term from 1993. Currently JITing

3080-514: Was meant to be completed by joined efforts of Adobe, Mozilla and its community within the Tamarin Project, to ECMAScript Harmony . Adobe continued to use Tamarin in its Flash Player , but it did not replace SpiderMonkey as the JavaScript engine of Mozilla applications. The only part of Tamarin used in modern Mozilla applications (i.e. Firefox 3.5+) via SpiderMonkey is NanoJIT , a module that

3136-453: Was pioneered by James G. Mitchell in 1970, which he implemented for the experimental language LC² . Smalltalk (c. 1983) pioneered new aspects of JIT compilations. For example, translation to machine code was done on demand, and the result was cached for later use. When memory became scarce, the system would delete some of this code and regenerate it when it was needed again. Sun's Self language improved these techniques extensively and

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