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| QEMU | |
|---|---|
 | |
 The free operating systemOpenIndiana running within QEMU, which runs as a process onLinux | |
| Original author | Fabrice Bellard |
| Developers | QEMU team: Peter Maydell, et al. |
| Stable release | |
| Repository | gitlab |
| Written in | C |
| Operating system | Linux,Microsoft Windows,macOS and some otherUNIX platforms |
| Type | Hypervisor,emulator |
| License | GPL-2.0-only[2] |
| Website | www |
TheQuick Emulator (QEMU)[3] is afree and open-sourceemulator that uses dynamicbinary translation to emulate acomputer'sprocessor; that is, it translates the emulated binary codes to an equivalent binary format which is executed by the machine. It provides a variety of hardware and device models for the virtual machine, enabling it to run differentguest operating systems. QEMU can be used with aKernel-based Virtual Machine (KVM) to emulate hardware at near-native speeds. Additionally, it supportsuser-level processes, allowing applications compiled for one processor architecture to run on another.[4]
QEMU supports the emulation ofx86,ARM,PowerPC,RISC-V, andother architectures.
QEMU isfree software developed byFabrice Bellard. Different components of QEMU are licensed under theGNU General Public License (GPL),BSD license,GNU Lesser General Public License (LGPL), or other GPL-compatible licenses.[5]
QEMU has multiple operating modes:[6]
QEMU supports the emulation of various architectures, includingx86,MIPS64 (up to Release 6),[9]SPARC (sun4m and sun4u),ARM (Integrator/CP and Versatile/PB),SuperH,PowerPC (PReP andPower Macintosh),ETRAX CRIS,MicroBlaze, andRISC-V. It supports saving the 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 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 inQCOW format, which can significantly reduce image size. QCOW images only occupy the actual used disk space, not the full configured 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, which are files that store only the changes made from an original (unmodified) base image file. This enables the emulated disk's contents to be reverted to an earlier state. For instance, a base image could contain 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) that share the host system's connectivity by translating network addresses, effectively allowing 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 localTAP 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 integratedSMB server and network-port redirection (to allow incoming connections to the virtual machine). It can also boot Linux kernels without abootloader.
QEMU does not depend on the presence of graphical output methods on the host system. Instead, it provides access to the guest OS screen via an integratedVNC server. It can also use an emulated serial line without any screen, with applicable operating systems.
Simulating multiple CPUs runningSMP is possible.
QEMU does not require administrative rights to run unless additional kernel modules are used to improve speed (likeKQEMU) or certain modes of its network connectivity model are utilized.
The Tiny Code Generator (TCG) aims to remove the shortcoming of relying on a particular version ofGCC or anycompiler, instead incorporating the compiler 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 inTCG ops – a kind of machine-independent intermediate notation, and subsequently this notation being compiled for the host's architecture by TCG. Optional optimization passes are performed between them, for ajust-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 theTCG ops to. If no dedicated JIT code is available for the architecture, TCG falls back to a slowinterpreter mode called TCG Interpreter (TCI). It also requires updating the target code to use TCG ops instead of the oldDynGen ops.[clarification needed]
Starting with QEMU Version 0.10.0, TCG ships with the QEMU stable release. It replacesDynGen, which relied on GCC 3.x to work.[10][11]
KQEMU was aLinux kernelmodule, also written byFabrice Bellard, which notably sped up emulation of x86 or x86-64 guests on platforms with the same CPU architecture. This worked by runninguser mode code (and optionally some kernel code) directly on the host computer's CPU, and by using processor and peripheral emulation only forkernel-mode andreal-mode code. KQEMU could execute code from many guest operating systems even if the host CPU did not supporthardware-assisted virtualization. KQEMU was initially aclosed-source product available free of charge but starting from version 1.3.0pre10 (February 2007),[12] it wasrelicensed under theGNU General Public License. QEMU versions starting with 0.12.0 (as of August 2009[update]) support large memory which makes them incompatible with KQEMU.[13] Newer releases of QEMU have completely removed support for KQEMU.
QVM86 was aGNU 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 the Linux-based hardware-assisted virtualization solution for use with QEMU following the lack of support for KQEMU and QVM86.[citation needed] QEMU can also use KVM on other architectures likeARM andMIPS.[14]
Intel's Hardware Accelerated Execution Manager (HAXM) is an open-source alternative[15] to KVM for x86-based hardware-assisted virtualization on NetBSD, Linux, Windows and macOS usingIntel VT. As of 2013[update] Intel mostly solicits its use with QEMU for Android development.[16] Starting with version 2.9.0, the official QEMU includes support for HAXM, under the nameHax.[17]
QEMU also supports the following accelerators:[17]
Hypervisor.framework based on Intel VT.QEMU supports the followingdisk image formats:[18]
.dmg) – Read-only.hdd,.hds) – Read-only.qcow2,.qed,.qcow,.cow).vdi).vhd).vmdk).img) that contain sector-by-sector contents of a disk.iso) that contain sector-by-sector contents of an optical disk (e.g. booting live OSes)[19]TheQEMU Object Model (QOM) provides a framework for registering types that users can make and instantiating objects from those types.[20]
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 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 a built-indynamic re-compiler 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 re-compiler only as a fallback mechanism – for example, when guest code executes inreal mode.[21] In addition, VirtualBox did a lot of code analysis and patching using a built-in disassembler to minimize recompilation. VirtualBox is free and open-source (available underGPL), except for certain features.
Xen, a virtual machine monitor, can run in HVM (hardware virtual machine) mode, usingIntel VT-x orAMD-V hardwarex86 virtualization extensions andARMCortex-A7 andCortex-A15 virtualization extensions.[22] This means that instead of para-virtualized devices, a real set of virtual hardware is exposed to the DomU, enabling it to use real device drivers.
QEMU includes several components: CPU emulators, emulated devices, generic devices, machine descriptions, user interface, and a debugger. The emulated devices and generic devices in QEMU make up its device models for I/O virtualization.[23] 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.[24] APIC support is provided by Xen.
Xen-HVM utilizes device emulation based on the QEMU project to deliver I/O virtualization to virtual machines (VMs). Hardware is emulated through a QEMU "device model" daemon running as a backend in Dom0. Unlike other QEMU modes, such as dynamic translation or KVM, the hypervisor fully manages virtual CPUs, pausing them as necessary while QEMU handles memory-mapped I/O emulation.
KVM (Kernel-based Virtual Machine) is a FreeBSD and Linux kernel module that allows auser space program access to thehardware 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,[25] Win4Lin released Win4Lin Virtual Desktop Server based on 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 toVirtual 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.[26]
SerialICE 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 hardwarein-circuit emulators (ICE).[27]
WinUAE introduced support for theCyberStorm PPC and Blizzard 603e boards using the QEMU PPC core in version 3.0.0.[28]
Unicorn is a CPU emulation framework based on QEMU's "TCG" CPU emulator. Unlike QEMU, Unicorn focuses on the CPUonly: 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.[29]
Limbo is an x86 andARM64 QEMU-based virtual machine for Android.[30] It is one of the few pieces of virtual machine software available for Android capable of emulating Microsoft Windows,[31] although it 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.[32] Limbo was removed from the Google Play Store for unknown reasons between February 2019 and December 2020, though it can still be installed off the developer's website with anAPK (Android Package) installation.[33] Limbo tends to have issues regarding its audio quality and playback. No fixes have been found for these problems as of 2024.[34] 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 a basic Android keyboard cannot do in Limbo x86, such as the Ctrl, Alt, Del, and function keys.[35] It is recommended to install Hacker's Keyboard with an APK file, as the Google Play version says it doesn't work with newer versions of Android.[36][verification needed]
QEMU can emulate thei386 andx86_64 architectures. Besides thecentral processing unit (CPU) (which is also configurable and can emulate a number of Intel CPU models including as of 3 March 2018Sandy Bridge,[37]Ivy Bridge,[38]Haswell,[39]Broadwell[40][41] andSkylake[39]), the following devices are emulated:
TheBIOS implementation used by QEMU starting from version 0.12 isSeaBIOS. The VGA BIOS implementation of SeaBIOS is also used starting from version 2.0.0. TheUEFI firmware for QEMU is OVMF.[45]
QEMU emulates the followingPowerMac peripherals:
OpenBIOS is used as the firmware.
QEMU emulates the followingPREP peripherals:
On the PREP target,Open Hack'Ware, anOpen-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 theARMv7instruction set (and down to ARMv5TEJ) with NEON extension.[46] It emulates full systems like Integrator/CP board, Versatile baseboard, RealView Emulation baseboard, XScale-based PDAs, Palm Tungsten|E PDA,Nokia N800 andNokia N810 Internet tablets, etc. QEMU also powers the Android emulator which is part of theAndroid 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, SamsungExynos 4210 (dual-core Cortex-A9) and Versatile ExpressARM Cortex-A9ARM Cortex-A15 are emulated. In 1.6.0, the 32-bit instructions of the ARMv8 (AArch64) architecture are emulated, but 64-bit instructions are unsupported.
The Xilinx Cortex A9-based Zynq SoC includes the following components:
QEMU can emulate 64-bit "A-profile" CPUs that commonly run Linux such as theARM Cortex-A53,ARM Cortex-A57 and theARM Cortex-A72.[47] This allows it to emulate theRaspberry Pi 3 and 4.[48]
QEMU has support for both 32- and 64-bitSPARC architectures.
When the firmware in theJavaStation (sun4m Architecture) was updated to version 0.8.1,[49] Proll—aPROM replacement—was replaced withOpenBIOS in version 0.8.2.
QEMU emulates the followingsun4m/sun4c/sun4d peripherals:
QEMU emulatesSun4u (UltraSPARC PC-like machine),Sun4v (T1 PC-like machine), or genericNiagara (T1) machine with the following peripherals:
QEMU supports the following peripherals:
Supported peripherals:From theMilkymist SoC
External trees exist, supporting the following targets:
{{cite web}}: CS1 maint: postscript (link)HAXM is now open source
The Intel Hardware Accelerated Execution Manager (Intel® HAXM) is a hardware-assisted virtualization engine (hypervisor) that uses Intel Virtualization Technology (Intel® VT) to speed up Android app emulation on a host machine.
