Editing Binary translation (section)

== Dynamic binary translation ==
Dynamic binary translation (DBT) looks at a short sequence of code—typically on the order of a single [[basic block]]—then translates it and caches the resulting sequence. Code is only translated as it is discovered and when possible, and branch instructions are made to point to already translated and saved code ([[memoization]]).

Dynamic binary translation differs from simple emulation (eliminating the emulator's main read-decode-execute loop—a major performance bottleneck), paying for this by large overhead during translation time. This overhead is hopefully amortized as translated code sequences are executed multiple times.

More advanced dynamic translators employ [[dynamic recompilation]] where the translated code is instrumented to find out what portions are executed a large number of times, and these portions are [[compiler optimization|optimized]] aggressively. This technique is reminiscent of a [[JIT compiler]], and in fact such compilers (e.g. [[Sun Microsystems|Sun]]'s [[HotSpot (Java)|HotSpot]] technology) can be viewed as dynamic translators from a virtual instruction set (the [[bytecode]]) to a real one.

=== Examples for dynamic binary translations in software ===
* [[Apple Computer]] implemented a dynamic translating [[emulator]] for [[Motorola 68000 series|M68K]] code in their [[PowerPC]] line of [[Apple Macintosh|Macintoshes]],<ref name="Wharton_1994"/> which achieved a very high level of reliability, performance and compatibility (see [[Mac 68K emulator]]). This allowed Apple to bring the machines to market with only a partially native [[operating system]], and end users could adopt the new, faster architecture without risking their investment in software. Partly because the emulator was so successful, many parts of the operating system remained emulated. A full transition to a PowerPC native [[operating system]] (OS) was not made until the release of [[Mac OS X]] (10.0) in 2001. (The Mac OS X "[[Classic (Mac OS X)|Classic]]" runtime environment continued to offer this emulation capability on PowerPC Macs until [[Mac OS X 10.5]].)
* [[Mac OS X 10.4|Mac OS X 10.4.4]] for Intel-based Macs introduced the [[Rosetta (software)|Rosetta]] dynamic translation layer to ease Apple's transition from PPC-based hardware to x86. Developed for Apple by [[Transitive Corporation]], the Rosetta software is an implementation of Transitive's [[QuickTransit]] solution.
* QuickTransit during its product lifespan also provided [[SPARC]]→[[x86]], x86→[[PowerPC]] and [[MIPS architecture|MIPS]]→[[Itanium 2]] translation support.
* [[Digital Equipment Corporation|DEC]] achieved similar success with its translation tools to help users migrate from the [[Complex instruction set computer|CISC]] [[VAX]] architecture to the [[DEC Alpha|Alpha]] [[RISC]] architecture.{{citation needed|date=July 2011}}
* [[Hewlett-Packard|HP]] ARIES (Automatic Re-translation and Integrated Environment Simulation) is a software<ref>{{cite book |url=https://books.google.com/books?id=1hQ7ngEACAAJ |publisher=Prentice Hall PTR |date=2003 |title=Itanium Rising: Breaking Through Moore's Second Law of Computing Power |author-first1=Jim |author-last1=Carlson |author-first2=Jerry |author-last2=Huck |access-date=2015-01-09 |isbn=978-0-13046415-6}}</ref> dynamic binary translation system that combines fast code interpretation with two phase dynamic translation to transparently and accurately execute [[HP 9000]] [[HP-UX]] applications on [[HP-UX]] 11i for [[HPE Integrity Servers]].<ref>{{cite web |url=http://h21007.www2.hp.com/portal/site/dspp/menuitem.863c3e4cbcdc3f3515b49c108973a801/?ciid=0208713ba4f02110713ba4f02110275d6e10RCRD |title=HP ARIES Dynamic Binary Translator |publisher=[[Hewlett-Packard|HP]] |access-date=2015-01-09 |archive-url=https://web.archive.org/web/20150110072830/http://h21007.www2.hp.com/portal/site/dspp/menuitem.863c3e4cbcdc3f3515b49c108973a801/?ciid=0208713ba4f02110713ba4f02110275d6e10RCRD |archive-date=2015-01-10 |url-status=dead}}</ref> The ARIES fast interpreter emulates a complete set of non-privileged [[PA-RISC]] instructions with no user intervention. During interpretation, it monitors the application's execution pattern and translates only the frequently executed code into native [[Itanium]] code at runtime. ARIES implements two phase dynamic translation, a technique in which translated code in first phase collects runtime profile information which is used during second phase translation to further optimize the translated code. ARIES stores the dynamically translated code in memory buffer called code cache. Further references to translated basic blocks execute directly in the code cache and do not require additional interpretation or translation. The targets of translated code blocks are back-patched to ensure execution takes place in code cache most of the time. At the end of the emulation, ARIES discards all the translated code without modifying the original application. The ARIES emulation engine also implements Environment Emulation which emulates an [[HP 9000]] [[HP-UX]] application's system calls, signal delivery, exception management, threads management, emulation of [[Hewlett-Packard|HP]] [[GDB]] for debugging, and core file creation for the application.
* DEC created the [[FX!32]] binary translator for converting [[x86]] applications to Alpha applications.<ref name="Wharton_1994"/>
* [[Sun Microsystems]]' [[Wabi (software)|Wabi]] software included dynamic translation from x86 to SPARC instructions.
* In January 2000, [[Transmeta]] Corporation announced a novel processor design named [[Transmeta Crusoe|Crusoe]].<ref>{{cite web |url=http://archive.arstechnica.com/cpu/1q00/crusoe/m-crusoe-1.html |title=Transmeta Crusoe Explored |author-first1=Jon |author-last1=Stokes |publisher=[[Ars Technica]] |access-date=2015-01-09}}</ref><ref>{{cite web |url=http://www.geek.com/procspec/features/transmeta/crusoe.htm |title=Transmeta's Crusoe Microprocessor |author-first=Rob |author-last=Hughes |date=January 20, 2000 |publisher=[[geek.com]] |archive-url=https://web.archive.org/web/20070927184520/http://www.geek.com/procspec/features/transmeta/crusoe.htm |archive-date=September 27, 2007 |url-status=dead}}</ref> From the [[FAQ]]<ref>{{cite web |url=http://www.transmeta.com/crusoe/faq.html |title=Transmeta Crusoe Processor Frequently Asked Questions FAQ |publisher=[[Transmeta]] |date=2007 |archive-url=https://web.archive.org/web/20070110213448/http://www.transmeta.com/crusoe/faq.html |archive-date=2007-01-10 |url-status=dead}}</ref> on their web site, {{quote|''The smart microprocessor consists of a hardware [[VLIW]] core as its engine and a software layer called Code Morphing software. The Code Morphing software acts as a shell […] morphing or translating [[x86]] instructions to native Crusoe instructions. In addition, the Code Morphing software contains a dynamic compiler and code optimizer […] The result is increased performance at the least amount of power. […] [This] allows Transmeta to evolve the VLIW hardware and Code Morphing software separately without affecting the huge base of software applications.''}}
* [[Intel]] Corporation developed and implemented an [[IA-32 Execution Layer]] - a dynamic binary translator designed to support IA-32 applications on [[Itanium]]-based systems, which was included in [[Microsoft]] [[Windows Server]] for [[Itanium]] architecture, as well as in several flavors of [[Linux]], including [[Red Hat]] and [[SUSE Linux|Suse]].  It allowed IA-32 applications to run faster than they would using the native IA-32 mode on Itanium processors.
* [[Dolphin (emulator)|Dolphin]] (an emulator for the [[GameCube]]/[[Wii]]) performs JIT recompilation of PowerPC code to x86 and AArch64.
* [[Microsoft Virtual PC]] supports binary translation for 32-bit guest operating systems.
* [[VMware Workstation]] 12 or earlier are known to support binary translation for 32-bit guest operating systems.

=== Examples for dynamic binary translations in hardware ===
* [[Nvidia]] [[Tegra]] K1 Denver translates [[ARM architecture|ARM]] instructions over a slow hardware decoder to its native microcode instructions and uses a software binary translator for hot code.{{citation needed|date=February 2015}}