Cfront was the original compiler for C++ (then known as " C with Classes") from around 1983, which converted C++ to C; developed by Bjarne Stroustrup at AT&T Bell Labs. The preprocessor did not understand all of the language and much of the code was written via translations . Cfront had a complete parser , built symbol tables , and built a tree for each class , function , etc. Cfront was based on CPre, a C compiler started in 1979.
35-509: As Cfront was written in C++, it was a challenge to bootstrap on a machine without a C++ compiler/translator. Along with the Cfront C++ sources, a special "half-preprocessed" version of the C code resulting from compiling Cfront with itself was also provided. This C code was to be compiled with the native C compiler, and the resulting executable could then be used to compile the Cfront C++ sources. Most of
70-532: A P-code machine or virtual machine , that hide even the processor's instruction set . This is the approach followed by many interpreted languages such as AWK , and some languages like Java , which are meant to be compiled into some machine-independent intermediate representation code (such as bytecode ). This arrangement simplifies the task of language implementation and its adaptation to different machines, and improves efficiency of sophisticated language features such as reflective programming . It also allows
105-411: A compiler (or assembler ) written in the source programming language that it intends to compile. An initial core version of the compiler (the bootstrap compiler ) is generated in a different language (which could be assembly language); successive expanded versions of the compiler are developed using this minimal subset of the language. The problem of compiling a self-compiling compiler has been called
140-521: A LISP compiler in LISP at MIT in 1962, testing it inside an existing LISP interpreter. Once they had improved the compiler to the point where it could compile its own source code, it was self-hosting. The compiler as it exists on the standard compiler tape is a machine language program that was obtained by having the S-expression definition of the compiler work on itself through the interpreter. This technique
175-459: A compiler being maliciously modified to introduce covert backdoors in programs it compiles or even further replicate the malicious modification in future versions of the compiler itself, creating a perpetual cycle of distrust) and various attacks against binary trustworthiness, multiple projects are working to reduce the effort for not only bootstrapping from source but also allowing everyone to verify that source and executable correspond. These include
210-422: A complicated compiler running on a system that has little or no software on it involves a series of ever more sophisticated assemblers and compilers. Assemblers were the first language tools to bootstrap themselves. The first high-level language to provide such a bootstrap was NELIAC in 1958. The first widely used languages to do so were Burroughs B5000 Algol in 1961 and LISP in 1962. Hart and Levin wrote
245-618: A hierarchy of runtime systems, with the CPU itself—or actually its logic at the microcode layer or below—acting as the lowest-level runtime system. Some compiled or interpreted languages provide an interface that allows application code to interact directly with the runtime system. An example is the Thread class in the Java language . The class allows code (that is animated by one thread) to do things such as start and stop other threads. Normally, core aspects of
280-438: A language's behavior such as task scheduling and resource management are not accessible in this fashion. Higher-level behaviors implemented by a runtime system may include tasks such as drawing text on the screen or making an Internet connection. It is often the case that operating systems provide these kinds of behaviors as well, and when available, the runtime system is implemented as an abstraction layer that translates
315-484: A runtime system may also perform support services such as type checking , debugging , or code generation and optimization . The runtime system is also the gateway through which a running program interacts with the runtime environment . The runtime environment includes not only accessible state values, but also active entities with which the program can interact during execution. For example, environment variables are features of many operating systems, and are part of
350-406: A runtime system that implements the execution model's behavior. Most scholarly papers on runtime systems focus on the implementation details of parallel runtime systems. A notable example of a parallel runtime system is Cilk , a popular parallel programming model. The proto-runtime toolkit was created to simplify the creation of parallel runtime systems. In addition to execution model behavior,
385-555: A runtime system. One possible definition of runtime system behavior, among others, is "any behavior not directly attributable to the program itself". This definition includes putting parameters onto the stack before function calls, parallel execution of related behaviors, and disk I/O . By this definition, essentially every language has a runtime system, including compiled languages , interpreted languages , and embedded domain-specific languages . Even API -invoked standalone execution models, such as Pthreads ( POSIX threads ), have
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#1732877080342420-412: Is built twice in order to compare the outputs of the two stages. If they are different, either the bootstrap or the full compiler contains a bug. Bootstrapping a compiler has the following advantages: Note that some of these points assume that the language runtime is also written in the same language. If one needs to compile a compiler for language X written in language X, there is the issue of how
455-544: Is implemented by the Pthreads runtime system (this runtime system is often the OS kernel). As an extreme example, the physical CPU itself can be viewed as an implementation of the runtime system of a specific assembly language. In this view, the execution model is implemented by the physical CPU and memory systems. As an analogy, runtime systems for higher-level languages are themselves implemented using some other languages. This creates
490-500: Is only possible when an interpreter already exists for the very same language that is to be compiled. It borrows directly from the notion of running a program on itself as input, which is also used in various proofs in theoretical computer science , such as the variation of the proof that the halting problem is undecidable that uses Rice's Theorem . Due to security concerns regarding the Trusting Trust Attack (which involves
525-442: Is the case of using an application programming interface (API) to interact with a runtime system. The calls to that API look the same as calls to a regular software library , however at some point during the call the execution model changes. The runtime system implements an execution model different from that of the language the library is written in terms of. A person reading the code of a normal library would be able to understand
560-464: The C language is a particular set of instructions inserted by the compiler into the executable image. Among other things, these instructions manage the process stack, create space for local variables, and copy function call parameters onto the top of the stack. There are often no clear criteria for determining which language behaviors are part of the runtime system itself and which can be determined by any particular source program. For example, in C,
595-580: The chicken-or-egg problem in compiler design, and bootstrapping is a solution to this problem. Bootstrapping is a fairly common practice when creating a programming language . Many compilers for many programming languages are bootstrapped, including compilers for BASIC , ALGOL , C , C# , D , Pascal , PL/I , Haskell , Modula-2 , Oberon , OCaml , Common Lisp , Scheme , Go , Java , Elixir , Rust , Python , Scala , Nim , Eiffel , TypeScript , Vala , Zig and more. A typical bootstrap process works in three or four stages: The full compiler
630-483: The operating system (OS), among others. The compiler makes assumptions depending on the specific runtime system to generate correct code. Typically the runtime system will have some responsibility for setting up and managing the stack and heap , and may include features such as garbage collection , threads or other dynamic features built into the language. Every programming language specifies an execution model , and many implement at least part of that model in
665-544: The Bootstrappable builds project and the Reproducible builds project. Runtime system In computer programming , a runtime system or runtime environment is a sub-system that exists in the computer where a program is created, as well as in the computers where the program is intended to be run. The name comes from the compile time and runtime division from compiled languages , which similarly distinguishes
700-459: The application(s) running within that runtime environment. Any other code that tries to run, or any failures in the application(s), will break the runtime environment. Breaking the runtime environment in turn breaks the OS, stopping all processing and requiring a reboot. If the boot is from read-only memory, an extremely secure, simple, single-mission system is created. Examples of such directly bundled runtime systems include: The runtime system of
735-457: The computer processes involved in the creation of a program (compilation) and its execution in the target machine (the runtime). Most programming languages have some form of runtime system that provides an environment in which programs run. This environment may address a number of issues including the management of application memory , how the program accesses variables , mechanisms for passing parameters between procedures , interfacing with
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#1732877080342770-482: The execution model implemented by the runtime system. For example, the trap instruction is one method of switching execution models. This difference is what distinguishes an API-invoked execution model, such as Pthreads, from a usual software library. Both Pthreads calls and software library calls are invoked via an API, but Pthreads behavior cannot be understood in terms of the language of the call. Rather, Pthreads calls bring into play an outside execution model, which
805-413: The first compiler can be compiled. The different methods that are used in practice include: Methods for distributing compilers in source code include providing a portable bytecode version of the compiler, so as to bootstrap the process of compiling the compiler with itself. The T-diagram is a notation used to explain these compiler bootstrap techniques. In some cases, the most convenient way to get
840-427: The invocation of the runtime system into an invocation of the operating system. This hides the complexity or variations in the services offered by different operating systems. This also implies that the OS kernel can itself be viewed as a runtime system, and that the set of OS calls that invoke OS behaviors may be viewed as interactions with a runtime system. In the limit, the runtime system may provide services such as
875-452: The language until circa 1990, and many of the more obscure corner cases in C++ were related to its C++-to-C translation approach. A few remnants of Cfront's translation method are still found in today's C++ compilers; name mangling was originated by Cfront, as the relatively primitive linkers at the time did not support type information in symbols, and some template instantiation models are derived from Cfront's early efforts. C++ (and Cfront)
910-455: The library's behavior by just knowing the language the library was written in. However, a person reading the code of the API that invokes a runtime system would not be able to understand the behavior of the API call just by knowing the language the call was written in. At some point, via some mechanism, the execution model stops being that of the language the call is written in and switches over to being
945-455: The porting effort in getting Cfront running on a new machine was related to standard I/O. Cfront's C++ streams were closely tied in with the C library's buffered I/O streams, but there was little interaction with the rest of the C environment. The compiler could be ported to most System V derivatives without many changes, but BSD -based systems usually had many more variations in their C libraries and associated stdio structures. Cfront defined
980-497: The proto-runtime approach. Notable early examples of runtime systems are the interpreters for BASIC and Lisp . These environments also included a garbage collector . Forth is an early example of a language designed to be compiled into intermediate representation code; its runtime system was a virtual machine that interpreted that code. Another popular, if theoretical, example is Donald Knuth 's MIX computer. In C and later languages that supported dynamic memory allocation,
1015-426: The runtime environment. The object file, on one hand, may be missing information from the runtime environment that will be resolved by linking . On the other hand, the code in the object file still depends on assumptions in the runtime system; for example, a function may read parameters from a particular register or stack location, depending on the calling convention used by the runtime environment. Another example
1050-410: The runtime environment; a running program can access them via the runtime system. Likewise, hardware devices such as disks or DVD drives are active entities that a program can interact with via a runtime system. One unique application of a runtime environment is its use within an operating system that only allows it to run. In other words, from boot until power-down, the entire OS is dedicated to only
1085-695: The same program to be executed on any machine without an explicit recompiling step, a feature that has become very important since the proliferation of the World Wide Web . To speed up execution, some runtime systems feature just-in-time compilation to machine code. A modern aspect of runtime systems is parallel execution behaviors, such as the behaviors exhibited by mutex constructs in Pthreads and parallel section constructs in OpenMP . A runtime system with such parallel execution behaviors may be modularized according to
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1120-416: The semantics of a particular program and the runtime environment is reflected by the different ways of compiling a program: compiling source code to an object file that contains all the functions versus compiling an entire program to an executable binary. The object file will only contain assembly code relevant to the included functions, while the executable binary will contain additional code that implements
1155-428: The setup of the stack is part of the runtime system. It is not determined by the semantics of an individual program because the behavior is globally invariant: it holds over all executions. This systematic behavior implements the execution model of the language, as opposed to implementing semantics of the particular program (in which text is directly translated into code that computes results). This separation between
1190-428: The way cfront can process C++ source code into something that can be compiled by previously-available C compilers, cppfront processes source code written in new and experimental C++ 'syntax 2' into something that can be compiled by previously-available 'syntax 1' C++ compilers. Bootstrapping (compilers) In computer science , bootstrapping is the technique for producing a self-compiling compiler – that is,
1225-506: Was directly responsible for many improvements in Unix linkers and object file formats , as it was the first widely used language which required link-time type checking, weak symbols , and other similar features. Cfront 4.0 was abandoned in 1993 after a failed attempt to add exception support. The C++ language had grown beyond its capabilities; however a compiler with similar approach became available later, namely Comeau C/C++ . Analogous to
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