mingw/info/gdbint/Language-Support.html

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  19 <h2 class="chapter">Language Support</h2>
  20
  21    GDB's language support is mainly driven by the symbol reader,
  22 although it is possible for the user to set the source language
  23 manually.
  24
  25    GDB chooses the source language by looking at the extension
  26 of the file recorded in the debug info; <code>.c</code> means C, <code>.f</code>
  27 means Fortran, etc.  It may also use a special-purpose language
  28 identifier if the debug format supports it, like with DWARF.
  29
  30 <h3 class="section">Adding a Source Language to GDB</h3>
  31
  32    <p>To add other languages to GDB's expression parser, follow the
  33 following steps:
  34
  35      <dl>
  36 <dt><em>Create the expression parser.</em>
  37      <dd>
  38 This should reside in a file <code></code><var>lang</var><code>-exp.y</code>.  Routines for
  39 building parsed expressions into a <code>union exp_element</code> list are in
  40 <code>parse.c</code>.
  41
  42      <p>Since we can't depend upon everyone having Bison, and YACC produces
  43 parsers that define a bunch of global names, the following lines
  44 <strong>must</strong> be included at the top of the YACC parser, to prevent the
  45 various parsers from defining the same global names:
  46
  47      <pre class="example">          #define yyparse         <var>lang</var>_parse
  48           #define yylex           <var>lang</var>_lex
  49           #define yyerror         <var>lang</var>_error
  50           #define yylval          <var>lang</var>_lval
  51           #define yychar          <var>lang</var>_char
  52           #define yydebug         <var>lang</var>_debug
  53           #define yypact          <var>lang</var>_pact
  54           #define yyr1            <var>lang</var>_r1
  55           #define yyr2            <var>lang</var>_r2
  56           #define yydef           <var>lang</var>_def
  57           #define yychk           <var>lang</var>_chk
  58           #define yypgo           <var>lang</var>_pgo
  59           #define yyact           <var>lang</var>_act
  60           #define yyexca          <var>lang</var>_exca
  61           #define yyerrflag       <var>lang</var>_errflag
  62           #define yynerrs         <var>lang</var>_nerrs
  63           </pre>
  64
  65      <p>At the bottom of your parser, define a <code>struct language_defn</code> and
  66 initialize it with the right values for your language.  Define an
  67 <code>initialize_</code><var>lang</var><code></code> routine and have it call
  68 <code>add_language(</code><var>lang</var><code>_language_defn)</code> to tell the rest of GDB
  69 that your language exists.  You'll need some other supporting variables
  70 and functions, which will be used via pointers from your
  71 <code></code><var>lang</var><code>_language_defn</code>.  See the declaration of <code>struct
  72 language_defn</code> in <code>language.h</code>, and the other <code>*-exp.y</code> files,
  73 for more information.
  74
  75      <br><dt><em>Add any evaluation routines, if necessary</em>
  76      <dd>
  77 If you need new opcodes (that represent the operations of the language),
  78 add them to the enumerated type in <code>expression.h</code>.  Add support
  79 code for these operations in the <code>evaluate_subexp</code> function
  80 defined in the file <code>eval.c</code>.  Add cases
  81 for new opcodes in two functions from <code>parse.c</code>:
  82 <code>prefixify_subexp</code> and <code>length_of_subexp</code>.  These compute
  83 the number of <code>exp_element</code>s that a given operation takes up.
  84
  85      <br><dt><em>Update some existing code</em>
  86      <dd>
  87 Add an enumerated identifier for your language to the enumerated type
  88 <code>enum language</code> in <code>defs.h</code>.
  89
  90      <p>Update the routines in <code>language.c</code> so your language is included.
  91 These routines include type predicates and such, which (in some cases)
  92 are language dependent.  If your language does not appear in the switch
  93 statement, an error is reported.
  94
  95      <p>Also included in <code>language.c</code> is the code that updates the variable
  96 <code>current_language</code>, and the routines that translate the
  97 <code>language_</code><var>lang</var><code></code> enumerated identifier into a printable
  98 string.
  99
 100      <p>Update the function <code>_initialize_language</code> to include your
 101 language.  This function picks the default language upon startup, so is
 102 dependent upon which languages that GDB is built for.
 103
 104      <p>Update <code>allocate_symtab</code> in <code>symfile.c</code> and/or symbol-reading
 105 code so that the language of each symtab (source file) is set properly.
 106 This is used to determine the language to use at each stack frame level.
 107 Currently, the language is set based upon the extension of the source
 108 file.  If the language can be better inferred from the symbol
 109 information, please set the language of the symtab in the symbol-reading
 110 code.
 111
 112      <p>Add helper code to <code>print_subexp</code> (in <code>expprint.c</code>) to handle any new
 113 expression opcodes you have added to <code>expression.h</code>.  Also, add the
 114 printed representations of your operators to <code>op_print_tab</code>.
 115
 116      <br><dt><em>Add a place of call</em>
 117      <dd>
 118 Add a call to <code></code><var>lang</var><code>_parse()</code> and <code></code><var>lang</var><code>_error</code> in
 119 <code>parse_exp_1</code> (defined in <code>parse.c</code>).
 120
 121      <br><dt><em>Use macros to trim code</em>
 122      <dd>
 123 The user has the option of building GDB for some or all of the
 124 languages.  If the user decides to build GDB for the language
 125 <var>lang</var>, then every file dependent on <code>language.h</code> will have the
 126 macro <code>_LANG_</code><var>lang</var><code></code> defined in it.  Use <code>#ifdef</code>s to
 127 leave out large routines that the user won't need if he or she is not
 128 using your language.
 129
 130      <p>Note that you do not need to do this in your YACC parser, since if GDB
 131 is not build for <var>lang</var>, then <code></code><var>lang</var><code>-exp.tab.o</code> (the
 132 compiled form of your parser) is not linked into GDB at all.
 133
 134      <p>See the file <code>configure.in</code> for how GDB is configured
 135 for different languages.
 136
 137      <br><dt><em>Edit </em><code>Makefile.in</code><em></em>
 138      <dd>
 139 Add dependencies in <code>Makefile.in</code>.  Make sure you update the macro
 140 variables such as <code>HFILES</code> and <code>OBJS</code>, otherwise your code may
 141 not get linked in, or, worse yet, it may not get <code>tar</code>red into the
 142 distribution!
 143 </dl>
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