View source for Vx32

{{Short description|Software library}}
{{Unreferenced|date=September 2009}}
{{Infobox software
| name                   = Vx32
| title                  = Vx32
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| author                 =
| developer              = Bryan Ford, Russ Cox
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| discontinued           =
| latest release version = 0.12
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| operating system       = [[FreeBSD]], [[Linux]], [[Mac OS X]]
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| genre                  = [[Virtual machine|Application-level virtual machine]]
| license                =
| website                = http://pdos.csail.mit.edu/~baford/vm/
}}
The '''Vx32''' virtual extension environment is an [[virtual machine|application-level virtual machine]] implemented as an ordinary user-mode library and designed to run native [[x86]] code.  Applications can link with and use Vx32 in order to create safe, [[Operating system|OS]]-independent execution environments, in which to run untrusted [[Plug-in (computing)|plug-ins]] or other extensions written in any language that compiles to x86 code.
From the host processor's viewpoint, plug-ins running under the Vx32 [[virtual machine monitor]] run in the context of the application process itself, but the Vx32 library uses [[dynamic recompilation]] to prevent the "guest" plug-in code from accessing memory or jumping to instructions outside its designated sandbox.  The Vx32 library redirects any [[system call]]s the plug-in makes to the application itself rather than to the host operating system, thereby giving the application exclusive control over the [[Application programming interface|API]] and security environment in which the plug-in code executes.
Vx32 thus provides an application extension facility comparable in function to the [[Java virtual machine]] (JVM) or the [[Common Language Runtime]] (CLR), but with less overhead and with the ability to run code written in ''any'' language, [[type safety|safe]] or unsafe.  Vx32's primary disadvantage is that it is more difficult to make it run on non-x86 host processors.
==Criticism==
There are some disadvantages that have been proposed by critics of Vx32:
*Vx32 is closely tied to the [[IA-32|IA-32 instruction set]], which makes it difficult to use on non-x86 architectures
*The IA-32e (AMD64) mode cannot be used by guests (the host can still run in 64-bit mode), because of the use of segmentation which is inherent to Vx32's design
==References==
{{reflist}}
==External links==
*[http://pdos.csail.mit.edu/~baford/vm/ The Vx32 Virtual Extension Environment]
*[http://pdos.csail.mit.edu/papers/vx32:usenix08-abs.html Vx32: Lightweight User-level Sandboxing on the x86] - Paper presented at USENIX 2008
*[http://swtch.com/9vx/ 9vx] - A port of [[Plan 9 from Bell Labs]] to vx32.
*[http://www.midnight-labs.org/vxwin32/ vx32 for Win32] {{Webarchive|url=https://web.archive.org/web/20081003015343/http://www.midnight-labs.org/vxwin32/ |date=2008-10-03 }}
[[Category:Virtualization software]]
[[Category:Virtualization software for Linux]]
[[Category:X86 emulators]]