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238 lines
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238 lines
12 KiB
HTML
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<title>Language Versioning and Migration</title>
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<h1>Language Versioning and
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Migration</h1>
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<p>This document discusses the mechanisms within Ghidra which mitigate
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the impact of language modifications to existing user program
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files. There are two general classes of language modifications
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which can be supported by the language translation capabilities within
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Ghidra :<br>
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</p>
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<ol>
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<li><a href="#versioning"><span style="font-weight: bold;">Version
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Change</span></a> - caused by modifications to a specific
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language implementation which necessitates a re-disassembly of a programs
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instructions.</li>
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<li><a href="#forcedMigration"><span style="font-weight: bold;">Forced
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Language Migration</span></a> - caused when an existing language
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implementation is completely replaced by a new implementation (language
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name must be different). It is important that an "old" language
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file (<span style="font-style: italic;">*.lang</span>) be generated for
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a language before it is eliminated. A simple or custom
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language translator is required to facilitate the forced migration.<br>
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</li>
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</ol>
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<p>Any program opened within Ghidra whose language has had a version
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change or has been replaced by a new implementation will be forced to
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upgrade. This will prevent such a program file from being opened
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as immutable and will impose a delay due to the necessary
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re-disassembly of all instructions.</p>
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<p>In addition to a forced upgrade, Ghidra's <span
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style="font-style: italic;">Set Language</span> capability will allow
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a user to make certain transitions between similar language
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implementations. Such transitions are generally facilitated via a
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default translator, although certain limitations are imposed based upon
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address space sizes and register mappings.</p>
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<p>Any changes made to a Data Organization could impact the packing of
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components within a structure or union. While such changes should be avoided
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due to the possible fallout, any such change to a
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<span style="font-style: italic;">*.cspec</span> should be made
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in conjunction with a version change to all affected languages within
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the relevant <span style="font-style: italic;">*.ldefs</span> files. The
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resulting program upgrade will allow affected data types to be updated.
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<br>
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</p>
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<h2><a name="versioning"></a>Language Versioning</h2>
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<p>A language's version is specified as a<span
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style="font-style: italic;"> <major></span><span
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style="font-weight: bold; font-style: italic;">.</span><span
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style="font-style: italic;"><minor></span> number pair (e.g.,
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1.0). The decision to advance the major or minor version number
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should be based upon the following criteria:<br>
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</p>
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<ol>
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<li><span style="font-weight: bold;">Major Version Change</span> -
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caused by modifications to a specific
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language implementation which changes register addressing or context
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register schema. Addition of registers alone does not constitute
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a major or minor change.<br>
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</li>
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<li><span style="font-weight: bold;">Minor Version Change</span> -
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caused by modifications to a specific
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language implementation which changes existing instruction or
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subconstructor pattern matching. Pcode changes and addition of
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new instructions alone does not constitute a major or minor change.</li>
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</ol>
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<p>Anytime the major version number is advanced, the minor version
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number should be reset to zero. <br>
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</p>
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<p>Only major version changes utilize a <a href="#translators">Language
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Translator</a> to facilitate the language transition.<br>
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</p>
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<h2><a name="forcedMigration"></a>Forced Language Migration<br>
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</h2>
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<p>When eliminating an old language the following must be accomplished:<br>
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</p>
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<ol>
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<li>Establish a replacement language</li>
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<li>Generate <a href="#oldlang">old-language specification</a> file (<span
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style="font-style: italic;">*.lang</span>)<br>
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</li>
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<li>Establish one and only one <a href="#translators">Language
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Translator </a>from the final version of the eliminated language to
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its replacement language.<br>
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</li>
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</ol>
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<p>Before eliminating a language a corresponding "old" language file
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must be generated and stored somewhere within Ghidra's languages
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directory (<span style="font-style: italic;">core/languages/old</span>
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directory has been established for this purpose). In
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addition, a simple or custom <a href="#translators">Language Translator</a>
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must be established to facilitate the language migration to the
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replacement language. <br>
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</p>
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<p>An old-language file may be generated automatically while the
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language still exists using the <span
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style="font-style: italic; font-weight: bold;">GenerateOldLanguagePlugin
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</span>configured into Ghidra's project window. In addition, if
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appropriate, a draft simple Language Translator specification can
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generated provided the replacement language is also available.<br>
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</p>
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<p>To generate an old-language file and optionally a draft simple
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translator specification:<br>
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</p>
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<ul>
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<li>Choose the menu item File>Generate Old Language File...</li>
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<li>Select the language to be eliminated from the languages list and
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click <span style="font-weight: bold;">Generate...</span></li>
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<li>From the file chooser select the output directory, enter a
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suitable name for the file and click <span style="font-weight: bold;">Create</span></li>
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<li>Once the old-language file is generated you will be asked if you
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would like to <span style="font-weight: bold; font-style: italic;">Create
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a Simple Translator?</span> If the replacement language is
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complete and available you can click <span style="font-weight: bold;">Yes
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</span>and specify an output file with the file chooser.</li>
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</ul>
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<h2><a name="oldlang"></a>Old Language Specification (<span
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style="font-style: italic;">*.lang</span>)</h2>
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<p>An old-language specification file is used to describe the essential
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elements of a language needed to instantiate an old program using that
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language and to facilitate translation to a replacement language.<br>
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</p>
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<p>The specification file is an XML file which identifies a language's
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description, address spaces and named registers. Since it
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should be generated using the <span
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style="font-style: italic; font-weight: bold;">GenerateOldLanguagePlugin</span>,
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its syntax is not defined here.
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</p>
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<p><span style="font-style: italic; font-weight: bold;">Sample
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Old-Language Specification File:</span><br>
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</p>
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<pre><?xml version="1.0" encoding="UTF-8"?><br><language version="1" endian="big"><br> <description><br> <name>MyOldProcessorLanguage</name><br> <processor>MyOldProcessor</processor><br> <family>Motorola</family><br> <alias>MyOldProcessorLanguageAlias1</alias><br> <alias>MyOldProcessorLanguageAlias2</alias><br> </description><br> <spaces><br> <space name="ram" type="ram" size="4" default="yes" /><br> <space name="register" type="register" size="4" /><br> <space name="data" type="code" size="4" /><br> </spaces><br> <registers><br> <context_register name="contextreg" offset="0x40" bitsize="8"><br> <field name="ctxbit1" range="1,1" /><br> <field name="ctxbit0" range="0,0" /><br> </context_register><br> <register name="r0" offset="0x0" bitsize="32" /><br> <register name="r1" offset="0x4" bitsize="32" /><br> <register name="r2" offset="0x8" bitsize="32" /><br> <register name="r3" offset="0xc" bitsize="32" /><br> <register name="r4" offset="0x10" bitsize="32" /><br> </registers><br></language><br><br></pre>
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<h2><a name="translators"></a>Language Translators</h2>
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<p>A language translator facilitates the renaming of address spaces,
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and relocation/renaming of registers. In addition, stored
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register values can be transformed - although limited knowledge is
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available for decision making. Through the process of
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re-disassembly, language changes in instruction and subconstructor
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pattern matching is handled. Three forms of translators are
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supported:<br>
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</p>
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<ol>
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<li><span style="font-weight: bold;">Default Translator</span> - in
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the absence of a simple or custom translator, an attempt will be made
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to map all address spaces and registers. Stored register values
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for unmapped registers will be discarded. Forced language
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migration can not use a default translator since it is the presence of
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a translator with an old-language which specifies the migration path.<br>
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</li>
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<li><span style="font-weight: bold;">Simple Translator</span> -
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extends the behavior of the default translator allowing specific
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address space and register mappings to be specified via an XML file (<span
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style="font-style: italic;">*.trans</span>). See sample <a
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href="#transfile">Simple Translator Specification</a>.<br>
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</li>
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<li><span style="font-weight: bold;">Custom Translator</span> -
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custom translators can be written as a Java class which extends <span
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style="font-weight: bold; font-style: italic;">LanguageTranslatorAdapter</span>
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or implements <span style="font-weight: bold; font-style: italic;">LanguageTranslator</span>.
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This should generally be unnecessary but can provided additional
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flexibility. The default constructor must be public and will be used
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for instantiation. Extending <span
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style="font-weight: bold; font-style: italic;">LanguageTranslatorAdapter
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</span>will allow the default translator capabilities to be
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leveraged with minimal coding.</li>
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</ol>
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<span style="font-family: times new roman;"><span
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style="font-weight: bold;"></span></span>
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<p style="font-weight: bold; font-style: italic;"><a name="transfile"></a>Sample
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Simple Translator Specification File:</p>
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<pre><?xml version="1.0" encoding="UTF-8"?>
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<language_translation>
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<from_language version="1">MyOldProcessorLanguage</from_language>
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<to_language version="1">MyNewProcessorLanguage</to_language>
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<!--
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Obsolete space will be deleted with all code units in that space.
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-->
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<delete_space name="data" />
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<!--
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Spaces whose name has changed can be mapped over
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-->
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<map_space from="ram" to="ram" />
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<!--
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Registers whose name has changed can be mapped (size and offset changes are allowed)
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The map_register may include a size attribute although it is ignored.
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-->
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<map_register from="r0" to="cr0" />
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<map_register from="r1" to="cr1" />
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<!--
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All existing processor context can be cleared
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-->
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<clear_all_context/>
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<!--
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A specific context value can be painted across all of program memory
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NOTE: sets occur after clear_all_context
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-->
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<set_context name="ctxbit0" value="1"/>
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<!--
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Force a specific Java class which extends
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<i>ghidra.program.util.LanguagePostUpgradeInstructionHandler</i>
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to be invoked following translation and re-disassembly to allow for more
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complex instruction context transformations/repair.
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-->
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<post_upgrade_handler class="ghidra.program.language.MyOldNewProcessorInstructionRepair" />
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</language_translation>
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</pre>
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<p style="font-weight: bold; font-style: italic;">Translator Limitations<br>
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</p>
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<p>The current translation mechanism does not handle the potential need
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for complete re-disassembly and associated auto-analysis. <br>
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</p>
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</body>
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</html>
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