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132-498: QEMU supports the emulation of various processor architectures, including x86 , ARM , PowerPC , RISC-V , and others . QEMU is free software that was developed by Fabrice Bellard . Its different components are licensed under the GNU General Public License (GPL) , BSD license , GNU Lesser General Public License (LGPL), or other GPL-compatible licenses. QEMU has multiple operating modes: QEMU supports

264-618: A 64 KB (one segment) stack in memory supported by computer hardware . Only words (two bytes) can be pushed to the stack. The stack grows toward numerically lower addresses, with SS:SP pointing to the most recently pushed item. There are 256 interrupts , which can be invoked by both hardware and software. The interrupts can cascade, using the stack to store the return address . The original Intel 8086 and 8088 have fourteen 16- bit registers. Four of them (AX, BX, CX, DX) are general-purpose registers (GPRs), although each may have an additional purpose; for example, only CX can be used as

396-579: A backward compatible version of this functionality on the same microprocessor as the main processor. In addition to this, modern x86 designs also contain a SIMD -unit (see SSE below) where instructions can work in parallel on (one or two) 128-bit words, each containing two or four floating-point numbers (each 64 or 32 bits wide respectively), or alternatively, 2, 4, 8 or 16 integers (each 64, 32, 16 or 8 bits wide respectively). The presence of wide SIMD registers means that existing x86 processors can load or store up to 128 bits of memory data in

528-484: A garbage collector and debugger . Programs written in a high-level language are either directly executed by some kind of interpreter or converted into machine code by a compiler (and assembler and linker ) for the CPU to execute. While compilers (and assemblers) generally produce machine code directly executable by computer hardware, they can often (optionally) produce an intermediate form called object code . This

660-468: A variable-length code requiring 3, 6, 10, or 18 bits, and address operands include a "bit offset". Many BASIC interpreters can store and read back their own tokenized internal representation. An interpreter might well use the same lexical analyzer and parser as the compiler and then interpret the resulting abstract syntax tree . Example data type definitions for the latter, and a toy interpreter for syntax trees obtained from C expressions are shown in

792-466: A virtual machine , which is implemented not in hardware, but in the bytecode interpreter. Such compiling interpreters are sometimes also called compreters . In a bytecode interpreter each instruction starts with a byte, and therefore bytecode interpreters have up to 256 instructions, although not all may be used. Some bytecodes may take multiple bytes, and may be arbitrarily complicated. Control tables - that do not necessarily ever need to pass through

924-457: A base image could hold a fresh installation of a known working operating system, and overlay images can be used to record changes. Should the guest system become unusable (through virus attack, accidental system destruction, etc.), the user can delete the overlay and use an earlier emulated disk image. QEMU can emulate network cards (of different models) which share the host system's connectivity by translating network addresses, effectively allowing

1056-604: A basic Android keyboard cannot do in Limbo x86, such as the Ctrl, Alt, Del, and function keys. It is recommended to install Hacker's Keyboard with an APK file due to the Google Play Store stating it does not support newer Android versions; for an APK file allows installing Hacker's Keyboard on newer versions of Android. QEMU can emulate i386 and x86_64 architecture. Besides the CPU (which is also configurable and can emulate

1188-448: A built-in dynamic recompiler based on QEMU. As with KQEMU, VirtualBox runs nearly all guest code natively on the host via the VMM (Virtual Machine Manager) and uses the recompiler only as a fallback mechanism – for example, when guest code executes in real mode . In addition, VirtualBox did a lot of code analysis and patching using a built-in disassembler to minimize recompilation. VirtualBox

1320-441: A bytecode interpreter, because of nodes related to syntax performing no useful work, of a less sequential representation (requiring traversal of more pointers) and of overhead visiting the tree. Further blurring the distinction between interpreters, bytecode interpreters and compilation is just-in-time (JIT) compilation, a technique in which the intermediate representation is compiled to native machine code at runtime. This confers

1452-413: A compiler works. However, a compiled program still runs much faster, under most circumstances, in part because compilers are designed to optimize code, and may be given ample time for this. This is especially true for simpler high-level languages without (many) dynamic data structures, checks, or type checking . In traditional compilation, the executable output of the linkers (.exe files or .dll files or

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1584-439: A compiling phase - dictate appropriate algorithmic control flow via customized interpreters in similar fashion to bytecode interpreters. Threaded code interpreters are similar to bytecode interpreters but instead of bytes they use pointers. Each "instruction" is a word that points to a function or an instruction sequence, possibly followed by a parameter. The threaded code interpreter either loops fetching instructions and calling

1716-413: A computer language is usually done in relation to an abstract machine (so-called operational semantics ) or as a mathematical function ( denotational semantics ). A language may also be defined by an interpreter in which the semantics of the host language is given. The definition of a language by a self-interpreter is not well-founded (it cannot define a language), but a self-interpreter tells a reader about

1848-539: A counter with the loop instruction. Each can be accessed as two separate bytes (thus BX's high byte can be accessed as BH and low byte as BL). Two pointer registers have special roles: SP (stack pointer) points to the "top" of the stack , and BP (base pointer) is often used to point at some other place in the stack, typically above the local variables (see frame pointer ). The registers SI, DI, BX and BP are address registers , and may also be used for array indexing. One of four possible 'segment registers' (CS, DS, SS and ES)

1980-499: A debugger. The emulated devices and generic devices in QEMU make up its device models for I/O virtualization. They comprise a PIIX3 IDE (with some rudimentary PIIX4 capabilities), Cirrus Logic or plain VGA emulated video, RTL8139 or E1000 network emulation, and ACPI support. APIC support is provided by Xen. Xen-HVM has device emulation based on the QEMU project to provide I/O virtualization to

2112-504: A host thread for each emulated virtual CPU (vCPU) for full system emulation. This depends on the guest being updated to support parallel system emulation, currently ARM, Alpha, HP-PA, PowerPC, RISC-V, s390x, x86, and Xtensa. Otherwise, a single thread is used to emulate all virtual CPUs (vCPUs), which executes each vCPU in a round-robin manner. VirtualBox , first released in January 2007, used some of QEMU's virtual hardware devices, and had

2244-418: A library, see picture) is typically relocatable when run under a general operating system, much like the object code modules are but with the difference that this relocation is done dynamically at run time, i.e. when the program is loaded for execution. On the other hand, compiled and linked programs for small embedded systems are typically statically allocated, often hard coded in a NOR flash memory, as there

2376-714: A list of these commands in the order a programmer wishes to execute them. Each command (also known as an Instruction ) contains the data the programmer wants to mutate, and information on how to mutate the data. For example, an interpreter might read ADD Books, 5 and interpret it as a request to add five to the Books variable . Interpreters have a wide variety of instructions which are specialized to perform different tasks, but you will commonly find interpreter instructions for basic mathematical operations , branching , and memory management , making most interpreters Turing complete . Many interpreters are also closely integrated with

2508-476: A major change to the architecture referred to as X86S (formerly known as X86-S). The S in X86S stands for "simplification", which aims to remove support for legacy execution modes and instructions. A processor implementing this proposal would start execution directly in long mode and would only support 64-bit operating systems. 32-bit code would only be supported for user applications running in ring 3, and would use

2640-547: A memory location. However, this memory operand may also be the destination (or a combined source and destination), while the other operand, the source, can be either register or immediate. Among other factors, this contributes to a code size that rivals eight-bit machines and enables efficient use of instruction cache memory. The relatively small number of general registers (also inherited from its 8-bit ancestors) has made register-relative addressing (using small immediate offsets) an important method of accessing operands, especially on

2772-560: A more complex micro-op which fits the execution model better and thus can be executed faster or with fewer machine resources involved. Another way to try to improve performance is to cache the decoded micro-operations, so the processor can directly access the decoded micro-operations from a special cache, instead of decoding them again. Intel followed this approach with the Execution Trace Cache feature in their NetBurst microarchitecture (for Pentium 4 processors) and later in

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2904-431: A number of Intel CPU models including (as of 3 March 2018) Sandy Bridge , Ivy Bridge , Haswell , Broadwell and Skylake ), the following devices are emulated: The BIOS implementation used by QEMU starting from version 0.12 is SeaBIOS . The VGA BIOS implementation of SeaBIOS is also used starting from version 2.0.0. The UEFI firmware for QEMU is OVMF. QEMU emulates the following PowerMac peripherals: OpenBIOS

3036-439: A parse tree, and both may generate immediate instructions (for a stack machine , quadruple code , or by other means). The basic difference is that a compiler system, including a (built in or separate) linker, generates a stand-alone machine code program, while an interpreter system instead performs the actions described by the high-level program. A compiler can thus make almost all the conversions from source code semantics to

3168-405: A similar effect to obfuscation, but bytecode could be decoded with a decompiler or disassembler . The main disadvantage of interpreters is that an interpreted program typically runs more slowly than if it had been compiled . The difference in speeds could be tiny or great; often an order of magnitude and sometimes more. It generally takes longer to run a program under an interpreter than to run

3300-670: A single instruction and also perform bitwise operations (although not integer arithmetic ) on full 128-bits quantities in parallel. Intel's Sandy Bridge processors added the Advanced Vector Extensions (AVX) instructions, widening the SIMD registers to 256 bits. The Intel Initial Many Core Instructions implemented by the Knights Corner Xeon Phi processors, and the AVX-512 instructions implemented by

3432-494: A suitable interpreter. If the interpreter needs to be supplied along with the source, the overall installation process is more complex than delivery of a monolithic executable, since the interpreter itself is part of what needs to be installed. The fact that interpreted code can easily be read and copied by humans can be of concern from the point of view of copyright . However, various systems of encryption and obfuscation exist. Delivery of intermediate code, such as bytecode, has

3564-472: A template interpreter. Rather than implement the execution of code by virtue of a large switch statement containing every possible bytecode, while operating on a software stack or a tree walk, a template interpreter maintains a large array of bytecode (or any efficient intermediate representation) mapped directly to corresponding native machine instructions that can be executed on the host hardware as key value pairs (or in more efficient designs, direct addresses to

3696-415: A wide range of computational tasks, including binary emulation and internet applications. Interpreter performance is still a worry despite their adaptability, particularly on systems with limited hardware resources. Advanced instrumentation and tracing approaches provide insights into interpreter implementations and processor resource utilization during execution through evaluations of interpreters tailored for

3828-585: Is a QEMU-based firmware debugging tool running system firmware inside of QEMU while accessing real hardware through a serial connection to a host system. This can be used as a cheap replacement for hardware in-circuit emulators (ICE). WinUAE introduced support for the CyberStorm PPC and Blizzard 603e boards using the QEMU PPC core in version 3.0.0. Unicorn is a CPU emulation framework based on QEMU's "TCG” CPU emulator. Unlike QEMU, Unicorn focuses on

3960-461: Is a family of complex instruction set computer (CISC) instruction set architectures initially developed by Intel based on the 8086 microprocessor and its 8-bit-external-bus variant, the 8088 . The 8086 was introduced in 1978 as a fully 16-bit extension of 8-bit Intel's 8080 microprocessor, with memory segmentation as a solution for addressing more memory than can be covered by a plain 16-bit address. The term "x86" came into being because

4092-432: Is a few decades old, appearing in languages such as Smalltalk in the 1980s. Just-in-time compilation has gained mainstream attention amongst language implementers in recent years, with Java , the .NET Framework , most modern JavaScript implementations, and Matlab now including JIT compilers. Making the distinction between compilers and interpreters yet again even more vague is a special interpreter design known as

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4224-688: Is a layer of hardware-level instructions that implement higher-level machine code instructions or internal state machine sequencing in many digital processing elements. Microcode is used in general-purpose central processing units , as well as in more specialized processors such as microcontrollers , digital signal processors , channel controllers , disk controllers , network interface controllers , network processors , graphics processing units , and in other hardware. Microcode typically resides in special high-speed memory and translates machine instructions, state machine data or other input into sequences of detailed circuit-level operations. It separates

4356-536: Is a relatively simple way to achieve software compatibility between different products in a processor family. Even a non microcoding computer processor itself can be considered to be a parsing immediate execution interpreter that is written in a general purpose hardware description language such as VHDL to create a system that parses the machine code instructions and immediately executes them. Interpreters, such as those written in Java, Perl, and Tcl, are now necessary for

4488-470: Is allowed for almost all instructions. The largest native size for integer arithmetic and memory addresses (or offsets ) is 16, 32 or 64 bits depending on architecture generation (newer processors include direct support for smaller integers as well). Multiple scalar values can be handled simultaneously via the SIMD unit present in later generations, as described below. Immediate addressing offsets and immediate data may be expressed as 8-bit quantities for

4620-583: Is basically the same machine specific code but augmented with a symbol table with names and tags to make executable blocks (or modules) identifiable and relocatable. Compiled programs will typically use building blocks (functions) kept in a library of such object code modules. A linker is used to combine (pre-made) library files with the object file(s) of the application to form a single executable file. The object files that are used to generate an executable file are thus often produced at different times, and sometimes even by different languages (capable of generating

4752-439: Is compiled into "F code" (a bytecode), which is then interpreted by a virtual machine . In the spectrum between interpreting and compiling, another approach is to transform the source code into an optimized abstract syntax tree (AST), then execute the program following this tree structure, or use it to generate native code just-in-time . In this approach, each sentence needs to be parsed just once. As an advantage over bytecode,

4884-432: Is executed and then perform the desired action, whereas the compiled code just performs the action within a fixed context determined by the compilation. This run-time analysis is known as "interpretive overhead". Access to variables is also slower in an interpreter because the mapping of identifiers to storage locations must be done repeatedly at run-time rather than at compile time . There are various compromises between

5016-672: Is free and open-source (available under GPL ), except for certain features. Xen , a virtual machine monitor, can run in HVM (hardware virtual machine) mode, using Intel VT-x or AMD-V hardware x86 virtualization extensions and ARM Cortex-A7 and Cortex-A15 virtualization extensions. This means that instead of para-virtualized devices, a real set of virtual hardware is exposed to the DomU to use real device drivers to talk to. QEMU includes several components: CPU emulators, emulated devices, generic devices, machine descriptions, user interface, and

5148-430: Is implemented using closures in the interpreter language or implemented "manually" with a data structure explicitly storing the environment. The more features implemented by the same feature in the host language, the less control the programmer of the interpreter has; for example, a different behavior for dealing with number overflows cannot be realized if the arithmetic operations are delegated to corresponding operations in

5280-565: Is more difficult to maintain due to the interpreter having to support translation to multiple different architectures instead of a platform independent virtual machine/stack. To date, the only template interpreter implementations of widely known languages to exist are the interpreter within Java's official reference implementation, the Sun HotSpot Java Virtual Machine, and the Ignition Interpreter in

5412-449: Is often no secondary storage and no operating system in this sense. Historically, most interpreter systems have had a self-contained editor built in. This is becoming more common also for compilers (then often called an IDE ), although some programmers prefer to use an editor of their choice and run the compiler, linker and other tools manually. Historically, compilers predate interpreters because hardware at that time could not support both

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5544-463: Is one of the two modes only available in long mode . The addressing modes were not dramatically changed from 32-bit mode, except that addressing was extended to 64 bits, virtual addresses are now sign extended to 64 bits (in order to disallow mode bits in virtual addresses), and other selector details were dramatically reduced. In addition, an addressing mode was added to allow memory references relative to RIP (the instruction pointer ), to ease

5676-490: Is such a language, because XSLT programs are written in XML. A sub-domain of metaprogramming is the writing of domain-specific languages (DSLs). Clive Gifford introduced a measure quality of self-interpreter (the eigenratio), the limit of the ratio between computer time spent running a stack of N self-interpreters and time spent to run a stack of N − 1 self-interpreters as N goes to infinity. This value does not depend on

5808-708: Is ubiquitous in both stationary and portable personal computers, and is also used in midrange computers , workstations , servers, and most new supercomputer clusters of the TOP500 list. A large amount of software , including a large list of x86 operating systems are using x86-based hardware. Modern x86 is relatively uncommon in embedded systems , however, and small low power applications (using tiny batteries), and low-cost microprocessor markets, such as home appliances and toys, lack significant x86 presence. Simple 8- and 16-bit based architectures are common here, as well as simpler RISC architectures like RISC-V , although

5940-1001: Is underlining x86 as an example of how continuous refinement of established industry standards can resist the competition from completely new architectures. The table below lists processor models and model series implementing various architectures in the x86 family, in chronological order. Each line item is characterized by significantly improved or commercially successful processor microarchitecture designs. At various times, companies such as IBM , VIA , NEC , AMD , TI , STM , Fujitsu , OKI , Siemens , Cyrix , Intersil , C&T , NexGen , UMC , and DM&P started to design or manufacture x86 processors (CPUs) intended for personal computers and embedded systems. Other companies that designed or manufactured x86 or x87 processors include ITT Corporation , National Semiconductor , ULSI System Technology, and Weitek . Such x86 implementations were seldom simple copies but often employed different internal microarchitectures and different solutions at

6072-729: Is used as the firmware. QEMU emulates the following PREP peripherals: On the PREP target, Open Hack'Ware , an Open-Firmware -compatible BIOS, is used. QEMU can emulate the paravirtual sPAPR interface with the following peripherals: On the sPAPR target, another Open-Firmware-compatible BIOS is used, called SLOF. QEMU emulates the ARMv7 instruction set (and down to ARMv5TEJ) with NEON extension. It emulates full systems like Integrator/CP board, Versatile baseboard, RealView Emulation baseboard, XScale-based PDAs, Palm Tungsten|E PDA, Nokia N800 and Nokia N810 Internet tablets, etc. QEMU also powers

6204-491: Is used to form a memory address. In the original 8086 / 8088 / 80186 / 80188 every address was built from a segment register and one of the general purpose registers. For example ds:si is the notation for an address formed as [16 * ds + si] to allow 20-bit addressing rather than 16 bits, although this changed in later processors. At that time only certain combinations were supported. The FLAGS register contains flags such as carry flag , overflow flag and zero flag . Finally,

6336-458: The fstsw instruction, and it is common to simply use some of its bits for branching by copying it into the normal FLAGS. In the Intel 80286 , to support protected mode , three special registers hold descriptor table addresses (GDTR, LDTR, IDTR ), and a fourth task register (TR) is used for task switching. The 80287 is the floating-point coprocessor for the 80286 and has the same registers as

6468-525: The 6x86 was significantly faster than the Pentium on integer code. AMD later managed to grow into a serious contender with the K6 set of processors, which gave way to the very successful Athlon and Opteron . There were also other contenders, such as Centaur Technology (formerly IDT ), Rise Technology , and Transmeta . VIA Technologies ' energy efficient C3 and C7 processors, which were designed by

6600-496: The 80486 and all subsequent x86 models, the floating-point processing unit (FPU) is integrated on-chip. The Pentium MMX added eight 64-bit MMX integer vector registers (MM0 to MM7, which share lower bits with the 80-bit-wide FPU stack). With the Pentium III , Intel added a 32-bit Streaming SIMD Extensions (SSE) control/status register (MXCSR) and eight 128-bit SSE floating-point registers (XMM0 to XMM7). Starting with

6732-573: The AMD Opteron processor, the x86 architecture extended the 32-bit registers into 64-bit registers in a way similar to how the 16 to 32-bit extension took place. An R -prefix (for "register") identifies the 64-bit registers (RAX, RBX, RCX, RDX, RSI, RDI, RBP, RSP, RFLAGS, RIP), and eight additional 64-bit general registers (R8–R15) were also introduced in the creation of x86-64 . Also, eight more SSE vector registers (XMM8–XMM15) were added. However, these extensions are only usable in 64-bit mode, which

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6864-653: The Centaur company, were sold for many years following their release in 2005. Centaur's 2008 design, the VIA Nano , was their first processor with superscalar and speculative execution . It was introduced at about the same time (in 2008) as Intel introduced the Intel Atom , its first "in-order" processor after the P5 Pentium . Many additions and extensions have been added to the original x86 instruction set over

6996-437: The GNU General Public License . QEMU versions starting with 0.12.0 (as of August 2009) support large memory which makes them incompatible with KQEMU. Newer releases of QEMU have completely removed support for KQEMU. QVM86 was a GNU GPLv2 licensed drop-in replacement for the then closed-source KQEMU. The developers of QVM86 ceased development in January 2007. Kernel-based Virtual Machine ( KVM ) has mostly taken over as

7128-470: The IBM PC (1981) debut. As of June 2022 , most desktop and laptop computers sold are based on the x86 architecture family, while mobile categories such as smartphones or tablets are dominated by ARM . At the high end, x86 continues to dominate computation-intensive workstation and cloud computing segments. In the 1980s and early 1990s, when the 8088 and 80286 were still in common use,

7260-514: The Intel 8800 ), the Intel 960 , Intel 860 and the Intel/Hewlett-Packard Itanium architecture. However, the continuous refinement of x86 microarchitectures , circuitry and semiconductor manufacturing would make it hard to replace x86 in many segments. AMD's 64-bit extension of x86 (which Intel eventually responded to with a compatible design) and the scalability of x86 chips in the form of modern multi-core CPUs,

7392-427: The development speed when using an interpreter and the execution speed when using a compiler. Some systems (such as some Lisps ) allow interpreted and compiled code to call each other and to share variables. This means that once a routine has been tested and debugged under the interpreter it can be compiled and thus benefit from faster execution while other routines are being developed. Many interpreters do not execute

7524-620: The hardware virtualization features of various processors, with which QEMU can offer virtualization for x86, PowerPC, and S/390 guests. When the target architecture is the same as the host architecture, QEMU can make use of KVM particular features, such as acceleration. In early 2005, Win4Lin introduced Win4Lin Pro Desktop, based on a 'tuned' version of QEMU and KQEMU and it hosts NT-versions of Windows. In June 2006, Win4Lin released Win4Lin Virtual Desktop Server based on

7656-461: The machine code format was expanded. To provide backward compatibility, segments with executable code can be marked as containing either 16-bit or 32-bit instructions. Special prefixes allow inclusion of 32-bit instructions in a 16-bit segment or vice versa. The 80386 had an optional floating-point coprocessor, the 80387 ; it had eight 80-bit wide registers: st(0) to st(7), like the 8087 and 80287. The 80386 could also use an 80287 coprocessor. With

7788-424: The 8086-architecture), all together under the heading Microsystem 80 . However, this naming scheme was quite temporary, lasting for a few years during the early 1980s. Although the 8086 was primarily developed for embedded systems and small multi-user or single-user computers, largely as a response to the successful 8080-compatible Zilog Z80 , the x86 line soon grew in features and processing power. Today, x86

7920-471: The 8087 with the same data formats. With the advent of the 32-bit 80386 processor, the 16-bit general-purpose registers, base registers, index registers, instruction pointer, and FLAGS register , but not the segment registers, were expanded to 32 bits. The nomenclature represented this by prefixing an " E " (for "extended") to the register names in x86 assembly language . Thus, the AX register corresponds to

8052-655: The ARMv8 (AArch64) architecture are emulated, but 64-bit instructions are unsupported. The Xilinx Cortex A9-based Zynq SoC is modelled, with the following elements: QEMU can emulate 64-bit " A-profile " CPUs that commonly run Linux such as the ARM Cortex-A53 and the ARM Cortex-A72 . This allows it to emulate the Raspberry Pi 3 and 4. X86 x86 (also known as 80x86 or the 8086 family )

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8184-471: The AST keeps the global program structure and relations between statements (which is lost in a bytecode representation), and when compressed provides a more compact representation. Thus, using AST has been proposed as a better intermediate format for just-in-time compilers than bytecode. Also, it allows the system to perform better analysis during runtime. However, for interpreters, an AST causes more overhead than

8316-514: The Android emulator which is part of the Android SDK (most current Android implementations are ARM-based). Starting from version 2.0.0 of their Bada SDK, Samsung has chosen QEMU to help development on emulated 'Wave' devices. In 1.5.0 and 1.6.0, Samsung Exynos 4210 (dual-core Cortex-A9) and Versatile Express ARM Cortex-A9 ARM Cortex-A15 are emulated. In 1.6.0, the 32-bit instructions of

8448-495: The CPU only : no emulation of any peripherals is provided and raw binary code (outside of the context of an executable file or a system image) can be run directly. Unicorn is thread-safe and has multiple bindings and instrumentation interfaces. Limbo is an x86 and ARM64 QEMU-based virtual machine for Android. It is one of the few pieces of virtual machine software available for Android capable of emulating Microsoft Windows, although it

8580-585: The Decoded Stream Buffer (for Core-branded processors since Sandy Bridge). Transmeta used a completely different method in their Crusoe x86 compatible CPUs. They used just-in-time translation to convert x86 instructions to the CPU's native VLIW instruction set. Transmeta argued that their approach allows for more power efficient designs since the CPU can forgo the complicated decode step of more traditional x86 implementations. Addressing modes for 16-bit processor modes can be summarized by

8712-508: The Google V8 javascript execution engine. A self-interpreter is a programming language interpreter written in a programming language which can interpret itself; an example is a BASIC interpreter written in BASIC. Self-interpreters are related to self-hosting compilers . If no compiler exists for the language to be interpreted, creating a self-interpreter requires the implementation of

8844-877: The Knights Landing Xeon Phi processors and by Skylake-X processors, use 512-bit wide SIMD registers. During execution , current x86 processors employ a few extra decoding steps to split most instructions into smaller pieces called micro-operations. These are then handed to a control unit that buffers and schedules them in compliance with x86-semantics so that they can be executed, partly in parallel, by one of several (more or less specialized) execution units . These modern x86 designs are thus pipelined , superscalar , and also capable of out of order and speculative execution (via branch prediction , register renaming , and memory dependence prediction ), which means they may execute multiple (partial or complete) x86 instructions simultaneously, and not necessarily in

8976-555: The Linux-based hardware-assisted virtualization solution for use with QEMU following the lack of support for KQEMU and QVM86. QEMU can also use KVM on other architectures like ARM and MIPS . Intel's Hardware Accelerated Execution Manager ( HAXM ) is an open-source alternative to KVM for x86-based hardware-assisted virtualization on NetBSD, Linux, Windows and macOS using Intel VT . As of 2013 Intel mostly solicits its use with QEMU for Android development. Starting with version 2.9.0,

9108-676: The Lisp eval function could be implemented in machine code. The result was a working Lisp interpreter which could be used to run Lisp programs, or more properly, "evaluate Lisp expressions". The development of editing interpreters was influenced by the need for interactive computing. In the 1960s, the introduction of time-sharing systems allowed multiple users to access a computer simultaneously, and editing interpreters became essential for managing and modifying code in real-time. The first editing interpreters were likely developed for mainframe computers, where they were used to create and modify programs on

9240-516: The VMs. Hardware is emulated via a QEMU “device model” daemon running as a backend in Dom0. Unlike other QEMU running modes (dynamic translation or KVM), virtual CPUs are completely managed by the hypervisor, which takes care of stopping them while QEMU is emulating memory-mapped I/O accesses. KVM (Kernel-based Virtual Machine) is a FreeBSD and Linux kernel module that allows a user space program access to

9372-434: The advanced but delayed 5k86 ( K5 ), which, internally, was closely based on AMD's earlier 29K RISC design; similar to NexGen 's Nx586 , it used a strategy such that dedicated pipeline stages decode x86 instructions into uniform and easily handled micro-operations , a method that has remained the basis for most x86 designs to this day. Some early versions of these microprocessors had heat dissipation problems. The 6x86

9504-415: The amount of analysis performed before the program is executed. For example, Emacs Lisp is compiled to bytecode , which is a highly compressed and optimized representation of the Lisp source, but is not machine code (and therefore not tied to any particular hardware). This "compiled" code is then interpreted by a bytecode interpreter (itself written in C ). The compiled code in this case is machine code for

9636-415: The art, had been planned for 2021; as of March 2022 the release had not taken place, however. The instruction set architecture has twice been extended to a larger word size. In 1985, Intel released the 32-bit 80386 (later known as i386) which gradually replaced the earlier 16-bit chips in computers (although typically not in embedded systems ) during the following years; this extended programming model

9768-415: The box. Interpretation cannot be used as the sole method of execution: even though an interpreter can itself be interpreted and so on, a directly executed program is needed somewhere at the bottom of the stack because the code being interpreted is not, by definition, the same as the machine code that the CPU can execute. There is a spectrum of possibilities between interpreting and compiling, depending on

9900-418: The compiled code but it can take less time to interpret it than the total time required to compile and run it. This is especially important when prototyping and testing code when an edit-interpret-debug cycle can often be much shorter than an edit-compile-run-debug cycle. Interpreting code is slower than running the compiled code because the interpreter must analyze each statement in the program each time it

10032-519: The corresponding YMM register. Interpreter (computing) In computer science , an interpreter is a computer program that directly executes instructions written in a programming or scripting language , without requiring them previously to have been compiled into a machine language program. An interpreter generally uses one of the following strategies for program execution: Early versions of Lisp programming language and minicomputer and microcomputer BASIC dialects would be examples of

10164-446: The developer's website with an APK (Android Package) installation. Limbo tends to have issues regarding its audio quality and playback. No fixes have been found for these problems as of 2024. Overall, Limbo is less well-known than other virtual machine software, which leads to less available information regarding its troubleshooting. It is required to install an application known as "Hacker's Keyboard" to use many keyboard functions that

10296-436: The efficiency of running native code, at the cost of startup time and increased memory use when the bytecode or AST is first compiled. The earliest published JIT compiler is generally attributed to work on LISP by John McCarthy in 1960. Adaptive optimization is a complementary technique in which the interpreter profiles the running program and compiles its most frequently executed parts into native code. The latter technique

10428-569: The electronic and physical levels. Quite naturally, early compatible microprocessors were 16-bit, while 32-bit designs were developed much later. For the personal computer market, real quantities started to appear around 1990 with i386 and i486 compatible processors, often named similarly to Intel's original chips. After the fully pipelined i486 , in 1993 Intel introduced the Pentium brand name (which, unlike numbers, could be trademarked ) for their new set of superscalar x86 designs. With

10560-470: The emulation of various architectures, including x86, MIPS64 (up to Release 6), SPARC (sun4m and sun4u), ARM (Integrator/CP and Versatile/PB), SuperH , PowerPC ( PReP and Power Macintosh ), ETRAX CRIS , MicroBlaze , and RISC-V . It supports saving virtual machine state while all programs are running. Guest operating systems do not need patching to run inside QEMU. The virtual machine can interface with many types of physical host hardware, including

10692-401: The execution units with the decode steps opens up possibilities for more analysis of the (buffered) code stream, and therefore permits detection of operations that can be performed in parallel, simultaneously feeding more than one execution unit. The latest processors also do the opposite when appropriate; they combine certain x86 sequences (such as a compare followed by a conditional jump) into

10824-414: The expressiveness and elegance of a language. It also enables the interpreter to interpret its source code, the first step towards reflective interpreting. An important design dimension in the implementation of a self-interpreter is whether a feature of the interpreted language is implemented with the same feature in the interpreter's host language. An example is whether a closure in a Lisp -like language

10956-549: The first two actively produce modern 64-bit designs, leading to what has been called a "duopoly" of Intel and AMD in x86 processors. However, in 2014 the Shanghai-based Chinese company Zhaoxin , a joint venture between a Chinese company and VIA Technologies, began designing VIA based x86 processors for desktops and laptops. The release of its newest "7" family of x86 processors (e.g. KX-7000), which are not quite as fast as AMD or Intel chips but are still state of

11088-665: The first type. Perl , Raku , Python , MATLAB , and Ruby are examples of the second, while UCSD Pascal is an example of the third type. Source programs are compiled ahead of time and stored as machine independent code, which is then linked at run-time and executed by an interpreter and/or compiler (for JIT systems). Some systems, such as Smalltalk and contemporary versions of BASIC and Java , may also combine two and three types. Interpreters of various types have also been constructed for many languages traditionally associated with compilation, such as Algol , Fortran , Cobol , C and C++ . While interpretation and compilation are

11220-587: The fly. One of the earliest examples of an editing interpreter is the EDT (Editor and Debugger for the TECO) system, which was developed in the late 1960s for the PDP-1 computer. EDT allowed users to edit and debug programs using a combination of commands and macros, paving the way for modern text editors and interactive development environments. An interpreter usually consists of a set of known commands it can execute , and

11352-528: The formula: Addressing modes for 32-bit x86 processor modes can be summarized by the formula: Addressing modes for the 64-bit processor mode can be summarized by the formula: Instruction relative addressing in 64-bit code (RIP + displacement, where RIP is the instruction pointer register ) simplifies the implementation of position-independent code (as used in shared libraries in some operating systems). The 8086 had 64 KB of eight-bit (or alternatively 32 K-word of 16-bit ) I/O space, and

11484-399: The frequently occurring cases or contexts where a −128..127 range is enough. Typical instructions are therefore 2 or 3 bytes in length (although some are much longer, and some are single-byte). To further conserve encoding space, most registers are expressed in opcodes using three or four bits, the latter via an opcode prefix in 64-bit mode, while at most one operand to an instruction can be

11616-515: The functions they point to, or fetches the first instruction and jumps to it, and every instruction sequence ends with a fetch and jump to the next instruction. Unlike bytecode there is no effective limit on the number of different instructions other than available memory and address space. The classic example of threaded code is the Forth code used in Open Firmware systems: the source language

11748-532: The guest to use the same network as the host. The virtual network cards can also connect to network cards of other instances of QEMU or to local TAP interfaces. Network connectivity can also be achieved by bridging a TUN/TAP interface used by QEMU with a non-virtual Ethernet interface on the host OS using the host OS's bridging features. QEMU integrates several services to allow the host and guest systems to communicate: for example, an integrated SMB server and network-port redirection (to allow incoming connections to

11880-401: The host computer's CPU, and by using processor and peripheral emulation only for kernel-mode and real-mode code. KQEMU could execute code from many guest operating systems even if the host CPU did not support hardware-assisted virtualization . KQEMU was initially a closed-source product available free of charge, but starting from version 1.3.0pre10 (February 2007), it was relicensed under

12012-479: The host language. Some languages such as Lisp and Prolog have elegant self-interpreters. Much research on self-interpreters (particularly reflective interpreters) has been conducted in the Scheme programming language , a dialect of Lisp. In general, however, any Turing-complete language allows writing of its own interpreter. Lisp is such a language, because Lisp programs are lists of symbols and other lists. XSLT

12144-525: The host's architecture by TCG. Optional optimization passes are performed between them, for a just-in-time compiler (JIT) mode. TCG requires dedicated code written to support every architecture it runs on, so that the JIT knows what to translate the TCG ops to. If no dedicated JIT code is available for the architecture, TCG falls back to a slow interpreter mode called TCG Interpreter (TCI). It also requires updating

12276-501: The implementation of position-independent code , used in shared libraries in some operating systems. SIMD registers XMM0–XMM15 (XMM0–XMM31 when AVX-512 is supported). SIMD registers YMM0–YMM15 (YMM0–YMM31 when AVX-512 is supported). Lower half of each of the YMM registers maps onto the corresponding XMM register. SIMD registers ZMM0–ZMM31. Lower half of each of the ZMM registers maps onto

12408-408: The instruction pointer (IP) points to the next instruction that will be fetched from memory and then executed; this register cannot be directly accessed (read or written) by a program. The Intel 80186 and 80188 are essentially an upgraded 8086 or 8088 CPU, respectively, with on-chip peripherals added, and they have the same CPU registers as the 8086 and 8088 (in addition to interface registers for

12540-414: The interpreter and interpreted code and the typical batch environment of the time limited the advantages of interpretation. During the software development cycle , programmers make frequent changes to source code. When using a compiler, each time a change is made to the source code, they must wait for the compiler to translate the altered source files and link all of the binary code files together before

12672-564: The introduction of the 8086 and 8088, Intel added some complexity to its naming scheme and terminology as the "iAPX" of the ambitious but ill-fated Intel iAPX 432 processor was tried on the more successful 8086 family of chips, applied as a kind of system-level prefix. An 8086 system, including coprocessors such as 8087 and 8089 , and simpler Intel-specific system chips, was thereby described as an iAPX 86 system. There were also terms iRMX (for operating systems), iSBC (for single-board computers), and iSBX (for multimodule boards based on

12804-453: The language in a host language (which may be another programming language or assembler ). By having a first interpreter such as this, the system is bootstrapped and new versions of the interpreter can be developed in the language itself. It was in this way that Donald Knuth developed the TANGLE interpreter for the language WEB of the de-facto standard TeX typesetting system . Defining

12936-405: The language into native calls one opcode at a time rather than creating optimized sequences of CPU executable instructions from the entire code segment. Due to the interpreter's simple design of simply passing calls directly to the hardware rather than implementing them directly, it is much faster than every other type, even bytecode interpreters, and to an extent less prone to bugs, but as a tradeoff

13068-633: The limitations of computers at the time (e.g. a shortage of program storage space, or no native support for floating point numbers). Interpreters were also used to translate between low-level machine languages, allowing code to be written for machines that were still under construction and tested on computers that already existed. The first interpreted high-level language was Lisp . Lisp was first implemented by Steve Russell on an IBM 704 computer. Russell had read John McCarthy 's paper, "Recursive Functions of Symbolic Expressions and Their Computation by Machine, Part I", and realized (to McCarthy's surprise) that

13200-447: The lower 16 bits of the new 32-bit EAX register, SI corresponds to the lower 16 bits of ESI, and so on. The general-purpose registers, base registers, and index registers can all be used as the base in addressing modes, and all of those registers except for the stack pointer can be used as the index in addressing modes. Two new segment registers (FS and GS) were added. With a greater number of registers, instructions and operands,

13332-572: The machine instructions from the underlying electronics so that instructions can be designed and altered more freely. It also facilitates the building of complex multi-step instructions, while reducing the complexity of computer circuits. Writing microcode is often called microprogramming and the microcode in a particular processor implementation is sometimes called a microprogram . More extensive microcoding allows small and simple microarchitectures to emulate more powerful architectures with wider word length , more execution units and so on, which

13464-421: The machine level once and for all (i.e. until the program has to be changed) while an interpreter has to do some of this conversion work every time a statement or function is executed. However, in an efficient interpreter, much of the translation work (including analysis of types, and similar) is factored out and done only the first time a program, module, function, or even statement, is run, thus quite akin to how

13596-473: The name EM64T and finally using Intel 64. Microsoft and Sun Microsystems / Oracle also use term "x64", while many Linux distributions , and the BSDs also use the "amd64" term. Microsoft Windows, for example, designates its 32-bit versions as "x86" and 64-bit versions as "x64", while installation files of 64-bit Windows versions are required to be placed into a directory called "AMD64". In 2023, Intel proposed

13728-492: The names of several successors to Intel's 8086 processor end in "86", including the 80186 , 80286 , 80386 and 80486 . Colloquially, their names were "186", "286", "386" and "486". The term is not synonymous with IBM PC compatibility , as this implies a multitude of other computer hardware . Embedded systems and general-purpose computers used x86 chips before the PC-compatible market started , some of them before

13860-430: The native instructions), known as a "Template". When the particular code segment is executed the interpreter simply loads or jumps to the opcode mapping in the template and directly runs it on the hardware. Due to its design, the template interpreter very strongly resembles a just-in-time compiler rather than a traditional interpreter, however it is technically not a JIT due to the fact that it merely translates code from

13992-515: The official QEMU includes support for HAXM, under the name H ax . QEMU also supports the following accelerators: QEMU supports the following disk image formats: The QEMU Object Model (QOM) provides a framework for registering types that users can make and instantiating objects from those types. QOM provides the following features: Virtualization solutions that use QEMU can execute multiple virtual CPUs in parallel. For user-mode emulation, QEMU maps emulated threads to host threads. QEMU can run

14124-454: The peripherals). The 8086, 8088, 80186, and 80188 can use an optional floating-point coprocessor, the 8087 . The 8087 appears to the programmer as part of the CPU and adds eight 80-bit wide registers, st(0) to st(7), each of which can hold numeric data in one of seven formats: 32-, 64-, or 80-bit floating point, 16-, 32-, or 64-bit (binary) integer, and 80-bit packed decimal integer. It also has its own 16-bit status register accessible through

14256-410: The program being run. The book Structure and Interpretation of Computer Programs presents examples of meta-circular interpretation for Scheme and its dialects. Other examples of languages with a self-interpreter are Forth and Pascal . Microcode is a very commonly used technique "that imposes an interpreter between the hardware and the architectural level of a computer". As such, the microcode

14388-411: The program can be executed. The larger the program, the longer the wait. By contrast, a programmer using an interpreter does a lot less waiting, as the interpreter usually just needs to translate the code being worked on to an intermediate representation (or not translate it at all), thus requiring much less time before the changes can be tested. Effects are evident upon saving the source code and reloading

14520-458: The program. Compiled code is generally less readily debugged as editing, compiling, and linking are sequential processes that have to be conducted in the proper sequence with a proper set of commands. For this reason, many compilers also have an executive aid, known as a Makefile and program. The Makefile lists compiler and linker command lines and program source code files, but might take a simple command line menu input (e.g. "Make 3") which selects

14652-478: The same code base. Win4Lin Virtual Desktop Server serves Microsoft Windows sessions to thin clients from a Linux server. In September 2006, Win4Lin announced a change of the company name to Virtual Bridges with the release of Win4BSD Pro Desktop, a port of the product to FreeBSD and PC-BSD. Solaris support followed in May 2007 with the release of Win4Solaris Pro Desktop and Win4Solaris Virtual Desktop Server. SerialICE

14784-619: The same object format). A simple interpreter written in a low-level language (e.g. assembly ) may have similar machine code blocks implementing functions of the high-level language stored, and executed when a function's entry in a look up table points to that code. However, an interpreter written in a high-level language typically uses another approach, such as generating and then walking a parse tree , or by generating and executing intermediate software-defined instructions, or both. Thus, both compilers and interpreters generally turn source code (text files) into tokens, both may (or may not) generate

14916-418: The same order as given in the instruction stream. Some Intel CPUs ( Xeon Foster MP , some Pentium 4 , and some Nehalem and later Intel Core processors) and AMD CPUs (starting from Zen ) are also capable of simultaneous multithreading with two threads per core ( Xeon Phi has four threads per core). Some Intel CPUs support transactional memory ( TSX ). When introduced, in the mid-1990s, this method

15048-443: The same simplified segmentation as long mode. The x86 architecture is a variable instruction length, primarily " CISC " design with emphasis on backward compatibility . The instruction set is not typical CISC, however, but basically an extended version of the simple eight-bit 8008 and 8080 architectures. Byte-addressing is enabled and words are stored in memory with little-endian byte order. Memory access to unaligned addresses

15180-403: The shortcoming of relying on a particular version of GCC or any compiler, instead incorporating the compiler (code generator) into other tasks performed by QEMU at run time. The whole translation task thus consists of two parts: basic blocks of target code ( TBs ) being rewritten in TCG ops – a kind of machine-independent intermediate notation, and subsequently this notation being compiled for

15312-537: The source code as it stands but convert it into some more compact internal form. Many BASIC interpreters replace keywords with single byte tokens which can be used to find the instruction in a jump table . A few interpreters, such as the PBASIC interpreter, achieve even higher levels of program compaction by using a bit-oriented rather than a byte-oriented program memory structure, where commands tokens occupy perhaps 5 bits, nominally "16-bit" constants are stored in

15444-454: The stack. Much work has therefore been invested in making such accesses as fast as register accesses—i.e., a one cycle instruction throughput, in most circumstances where the accessed data is available in the top-level cache. A dedicated floating-point processor with 80-bit internal registers, the 8087 , was developed for the original 8086 . This microprocessor subsequently developed into the extended 80387 , and later processors incorporated

15576-456: The target code to use TCG ops instead of the old dyngen ops. Starting with QEMU Version 0.10.0, TCG ships with the QEMU stable release. It replaces dyngen , which relied on GCC 3.x to work. KQEMU was a Linux kernel module , also written by Fabrice Bellard , which notably sped up emulation of x86 or x86-64 guests on platforms with the same CPU architecture. This worked by running user mode code (and optionally some kernel code) directly on

15708-416: The term x86 usually represented any 8086-compatible CPU. Today, however, x86 usually implies binary compatibility with the 32-bit instruction set of the 80386 . This is due to the fact that this instruction set has become something of a lowest common denominator for many modern operating systems and also probably because the term became common after the introduction of the 80386 in 1985. A few years after

15840-506: The third group (set) of instructions then issues the commands to the compiler, and linker feeding the specified source code files. A compiler converts source code into binary instruction for a specific processor's architecture, thus making it less portable . This conversion is made just once, on the developer's environment, and after that the same binary can be distributed to the user's machines where it can be executed without further translation. A cross compiler can generate binary code for

15972-515: The two main means by which programming languages are implemented, they are not mutually exclusive, as most interpreting systems also perform some translation work, just like compilers. The terms " interpreted language " or " compiled language " signify that the canonical implementation of that language is an interpreter or a compiler, respectively. A high-level language is ideally an abstraction independent of particular implementations. Interpreters were used as early as 1952 to ease programming within

16104-410: The user machine even if it has a different processor than the machine where the code is compiled. An interpreted program can be distributed as source code. It needs to be translated in each final machine, which takes more time but makes the program distribution independent of the machine's architecture. However, the portability of interpreted source code is dependent on the target machine actually having

16236-459: The user's hard disks, CD-ROM drives, network cards, audio interfaces, and USB devices. USB devices can be emulated entirely, or the host's USB devices can be used, although this requires administrator privileges and does not work with some devices. Virtual disk images can be stored in Qcow format, which can significantly reduce image size. The size of stored QCOW images is what is actually used within

16368-425: The virtual disk, not its configured maximum capacity. This means a configured 120 GB disk may only occupy a few hundred megabytes on the host, as QCOW does not store unused disk space in the image file. The QCOW2 format also allows the creation of overlay images that record the difference from another (unmodified) base image file. This allows the emulated disk's contents to be reverted to an earlier state. For example,

16500-640: The virtual machine). It can also boot Linux kernels without a bootloader . QEMU does not depend on the presence of graphical output methods on the host system. Instead, it can allow one to access the guest OS screen via an integrated VNC server. It can also use an emulated serial line, without any screen, with applicable operating systems. Simulating multiple CPUs running SMP is possible. QEMU does not require administrative rights to run unless additional kernel modules are used to improve speed (like KQEMU ) or certain modes of its network connectivity model are utilized. The Tiny Code Generator (TCG) aims to remove

16632-490: The x86 naming scheme now legally cleared, other x86 vendors had to choose different names for their x86-compatible products, and initially some chose to continue with variations of the numbering scheme: IBM partnered with Cyrix to produce the 5x86 and then the very efficient 6x86 (M1) and 6x86 MX ( MII ) lines of Cyrix designs, which were the first x86 microprocessors implementing register renaming to enable speculative execution . AMD meanwhile designed and manufactured

16764-432: The x86-compatible VIA C7 , VIA Nano , AMD 's Geode , Athlon Neo and Intel Atom are examples of 32- and 64-bit designs used in some relatively low-power and low-cost segments. There have been several attempts, including by Intel, to end the market dominance of the "inelegant" x86 architecture designed directly from the first simple 8-bit microprocessors. Examples of this are the iAPX 432 (a project originally named

16896-484: The years, almost consistently with full backward compatibility . The architecture family has been implemented in processors from Intel, Cyrix , AMD , VIA Technologies and many other companies; there are also open implementations, such as the Zet SoC platform (currently inactive). Nevertheless, of those, only Intel, AMD, VIA Technologies, and DM&P Electronics hold x86 architectural licenses, and from these, only

17028-537: Was also affected by a few minor compatibility problems, the Nx586 lacked a floating-point unit (FPU) and (the then crucial) pin-compatibility, while the K5 had somewhat disappointing performance when it was (eventually) introduced. Customer ignorance of alternatives to the Pentium series further contributed to these designs being comparatively unsuccessful, despite the fact that the K5 had very good Pentium compatibility and

17160-624: Was designed to emulate Linux and DOS. Unlike other QEMU-based emulators, it does not require users to type commands to use, instead having a user interface to set the virtual machine's settings. It is more popular in developing countries in Asia such as India, Malaysia, and Thailand on YouTube due to the high usage of the Android Operating System. Limbo was removed from the Google Play Store for unknown reasons between February 2019 and December 2020, though it can still be installed off

17292-403: Was originally referred to as the i386 architecture (like its first implementation) but Intel later dubbed it IA-32 when introducing its (unrelated) IA-64 architecture. In 1999–2003, AMD extended this 32-bit architecture to 64 bits and referred to it as x86-64 in early documents and later as AMD64 . Intel soon adopted AMD's architectural extensions under the name IA-32e, later using

17424-436: Was sometimes referred to as a "RISC core" or as "RISC translation", partly for marketing reasons, but also because these micro-operations share some properties with certain types of RISC instructions. However, traditional microcode (used since the 1950s) also inherently shares many of the same properties; the new method differs mainly in that the translation to micro-operations now occurs asynchronously. Not having to synchronize

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