gxxint_15.html (11113B)
1 <HTML> 2 <HEAD> 3 <!-- This HTML file has been created by texi2html 1.52 4 from gxxint.texi on 27 August 1999 --> 5 6 <TITLE>G++ internals - Mangling</TITLE> 7 </HEAD> 8 <BODY> 9 Go to the <A HREF="gxxint_1.html">first</A>, <A HREF="gxxint_14.html">previous</A>, <A HREF="gxxint_16.html">next</A>, <A HREF="gxxint_16.html">last</A> section, <A HREF="gxxint_toc.html">table of contents</A>. 10 <P><HR><P> 11 12 13 <H2><A NAME="SEC20" HREF="gxxint_toc.html#TOC20">Function name mangling for C++ and Java</A></H2> 14 15 <P> 16 Both C++ and Jave provide overloaded function and methods, 17 which are methods with the same types but different parameter lists. 18 Selecting the correct version is done at compile time. 19 Though the overloaded functions have the same name in the source code, 20 they need to be translated into different assembler-level names, 21 since typical assemblers and linkers cannot handle overloading. 22 This process of encoding the parameter types with the method name 23 into a unique name is called <EM>name mangling</EM>. The inverse 24 process is called <EM>demangling</EM>. 25 26 </P> 27 <P> 28 It is convenient that C++ and Java use compatible mangling schemes, 29 since the makes life easier for tools such as gdb, and it eases 30 integration between C++ and Java. 31 32 </P> 33 <P> 34 Note there is also a standard "Jave Native Interface" (JNI) which 35 implements a different calling convention, and uses a different 36 mangling scheme. The JNI is a rather abstract ABI so Java can call methods 37 written in C or C++; 38 we are concerned here about a lower-level interface primarily 39 intended for methods written in Java, but that can also be used for C++ 40 (and less easily C). 41 42 </P> 43 44 45 <H3><A NAME="SEC21" HREF="gxxint_toc.html#TOC21">Method name mangling</A></H3> 46 47 <P> 48 C++ mangles a method by emitting the function name, followed by <CODE>__</CODE>, 49 followed by encodings of any method qualifiers (such as <CODE>const</CODE>), 50 followed by the mangling of the method's class, 51 followed by the mangling of the parameters, in order. 52 53 </P> 54 <P> 55 For example <CODE>Foo::bar(int, long) const</CODE> is mangled 56 as <SAMP>`bar__C3Fooil'</SAMP>. 57 58 </P> 59 <P> 60 For a constructor, the method name is left out. 61 That is <CODE>Foo::Foo(int, long) const</CODE> is mangled 62 as <SAMP>`__C3Fooil'</SAMP>. 63 64 </P> 65 <P> 66 GNU Java does the same. 67 68 </P> 69 70 71 <H3><A NAME="SEC22" HREF="gxxint_toc.html#TOC22">Primitive types</A></H3> 72 73 <P> 74 The C++ types <CODE>int</CODE>, <CODE>long</CODE>, <CODE>short</CODE>, <CODE>char</CODE>, 75 and <CODE>long long</CODE> are mangled as <SAMP>`i'</SAMP>, <SAMP>`l'</SAMP>, 76 <SAMP>`s'</SAMP>, <SAMP>`c'</SAMP>, and <SAMP>`x'</SAMP>, respectively. 77 The corresponding unsigned types have <SAMP>`U'</SAMP> prefixed 78 to the mangling. The type <CODE>signed char</CODE> is mangled <SAMP>`Sc'</SAMP>. 79 80 </P> 81 <P> 82 The C++ and Java floating-point types <CODE>float</CODE> and <CODE>double</CODE> 83 are mangled as <SAMP>`f'</SAMP> and <SAMP>`d'</SAMP> respectively. 84 85 </P> 86 <P> 87 The C++ <CODE>bool</CODE> type and the Java <CODE>boolean</CODE> type are 88 mangled as <SAMP>`b'</SAMP>. 89 90 </P> 91 <P> 92 The C++ <CODE>wchar_t</CODE> and the Java <CODE>char</CODE> types are 93 mangled as <SAMP>`w'</SAMP>. 94 95 </P> 96 <P> 97 The Java integral types <CODE>byte</CODE>, <CODE>short</CODE>, <CODE>int</CODE> 98 and <CODE>long</CODE> are mangled as <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>, 99 and <SAMP>`x'</SAMP>, respectively. 100 101 </P> 102 <P> 103 C++ code that has included <CODE>javatypes.h</CODE> will mangle 104 the typedefs <CODE>jbyte</CODE>, <CODE>jshort</CODE>, <CODE>jint</CODE> 105 and <CODE>jlong</CODE> as respectively <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>, 106 and <SAMP>`x'</SAMP>. (This has not been implemented yet.) 107 108 </P> 109 110 111 <H3><A NAME="SEC23" HREF="gxxint_toc.html#TOC23">Mangling of simple names</A></H3> 112 113 <P> 114 A simple class, package, template, or namespace name is 115 encoded as the number of characters in the name, followed by 116 the actual characters. Thus the class <CODE>Foo</CODE> 117 is encoded as <SAMP>`3Foo'</SAMP>. 118 119 </P> 120 <P> 121 If any of the characters in the name are not alphanumeric 122 (i.e not one of the standard ASCII letters, digits, or '_'), 123 or the initial character is a digit, then the name is 124 mangled as a sequence of encoded Unicode letters. 125 A Unicode encoding starts with a <SAMP>`U'</SAMP> to indicate 126 that Unicode escapes are used, followed by the number of 127 bytes used by the Unicode encoding, followed by the bytes 128 representing the encoding. ASSCI letters and 129 non-initial digits are encoded without change. However, all 130 other characters (including underscore and initial digits) are 131 translated into a sequence starting with an underscore, 132 followed by the big-endian 4-hex-digit lower-case encoding of the character. 133 134 </P> 135 <P> 136 If a method name contains Unicode-escaped characters, the 137 entire mangled method name is followed by a <SAMP>`U'</SAMP>. 138 139 </P> 140 <P> 141 For example, the method <CODE>X\u0319::M\u002B(int)</CODE> is encoded as 142 <SAMP>`M_002b__U6X_0319iU'</SAMP>. 143 144 </P> 145 146 147 <H3><A NAME="SEC24" HREF="gxxint_toc.html#TOC24">Pointer and reference types</A></H3> 148 149 <P> 150 A C++ pointer type is mangled as <SAMP>`P'</SAMP> followed by the 151 mangling of the type pointed to. 152 153 </P> 154 <P> 155 A C++ reference type as mangled as <SAMP>`R'</SAMP> followed by the 156 mangling of the type referenced. 157 158 </P> 159 <P> 160 A Java object reference type is equivalent 161 to a C++ pointer parameter, so we mangle such an parameter type 162 as <SAMP>`P'</SAMP> followed by the mangling of the class name. 163 164 </P> 165 166 167 <H3><A NAME="SEC25" HREF="gxxint_toc.html#TOC25">Qualified names</A></H3> 168 169 <P> 170 Both C++ and Java allow a class to be lexically nested inside another 171 class. C++ also supports namespaces (not yet implemented by G++). 172 Java also supports packages. 173 174 </P> 175 <P> 176 These are all mangled the same way: First the letter <SAMP>`Q'</SAMP> 177 indicates that we are emitting a qualified name. 178 That is followed by the number of parts in the qualified name. 179 If that number is 9 or less, it is emitted with no delimiters. 180 Otherwise, an underscore is written before and after the count. 181 Then follows each part of the qualified name, as described above. 182 183 </P> 184 <P> 185 For example <CODE>Foo::\u0319::Bar</CODE> is encoded as 186 <SAMP>`Q33FooU5_03193Bar'</SAMP>. 187 188 </P> 189 190 191 <H3><A NAME="SEC26" HREF="gxxint_toc.html#TOC26">Templates</A></H3> 192 193 <P> 194 A class template instantiation is encoded as the letter <SAMP>`t'</SAMP>, 195 followed by the encoding of the template name, followed 196 the number of template parameters, followed by encoding of the template 197 parameters. If a template parameter is a type, it is written 198 as a <SAMP>`Z'</SAMP> followed by the encoding of the type. 199 200 </P> 201 <P> 202 A function template specialization (either an instantiation or an 203 explicit specialization) is encoded by an <SAMP>`H'</SAMP> followed by the 204 encoding of the template parameters, as described above, followed by 205 an <SAMP>`_'</SAMP>, the encoding of the argument types template function (not the 206 specialization), another <SAMP>`_'</SAMP>, and the return type. (Like the 207 argument types, the return type is the return type of the function 208 template, not the specialization.) Template parameters in the argument 209 and return types are encoded by an <SAMP>`X'</SAMP> for type parameters, or a 210 <SAMP>`Y'</SAMP> for constant parameters, and an index indicating their position 211 in the template parameter list declaration. 212 213 </P> 214 215 216 <H3><A NAME="SEC27" HREF="gxxint_toc.html#TOC27">Arrays</A></H3> 217 218 <P> 219 C++ array types are mangled by emitting <SAMP>`A'</SAMP>, followed by 220 the length of the array, followed by an <SAMP>`_'</SAMP>, followed by 221 the mangling of the element type. Of course, normally 222 array parameter types decay into a pointer types, so you 223 don't see this. 224 225 </P> 226 <P> 227 Java arrays are objects. A Java type <CODE>T[]</CODE> is mangled 228 as if it were the C++ type <CODE>JArray<T></CODE>. 229 For example <CODE>java.lang.String[]</CODE> is encoded as 230 <SAMP>`Pt6JArray1ZPQ34java4lang6String'</SAMP>. 231 232 </P> 233 234 235 <H3><A NAME="SEC28" HREF="gxxint_toc.html#TOC28">Table of demangling code characters</A></H3> 236 237 <P> 238 The following special characters are used in mangling: 239 240 </P> 241 <DL COMPACT> 242 243 <DT><SAMP>`A'</SAMP> 244 <DD> 245 Indicates a C++ array type. 246 247 <DT><SAMP>`b'</SAMP> 248 <DD> 249 Encodes the C++ <CODE>bool</CODE> type, 250 and the Java <CODE>boolean</CODE> type. 251 252 <DT><SAMP>`c'</SAMP> 253 <DD> 254 Encodes the C++ <CODE>char</CODE> type, and the Java <CODE>byte</CODE> type. 255 256 <DT><SAMP>`C'</SAMP> 257 <DD> 258 A modifier to indicate a <CODE>const</CODE> type. 259 Also used to indicate a <CODE>const</CODE> member function 260 (in which cases it precedes the encoding of the method's class). 261 262 <DT><SAMP>`d'</SAMP> 263 <DD> 264 Encodes the C++ and Java <CODE>double</CODE> types. 265 266 <DT><SAMP>`e'</SAMP> 267 <DD> 268 Indicates extra unknown arguments <CODE>...</CODE>. 269 270 <DT><SAMP>`f'</SAMP> 271 <DD> 272 Encodes the C++ and Java <CODE>float</CODE> types. 273 274 <DT><SAMP>`F'</SAMP> 275 <DD> 276 Used to indicate a function type. 277 278 <DT><SAMP>`H'</SAMP> 279 <DD> 280 Used to indicate a template function. 281 282 <DT><SAMP>`i'</SAMP> 283 <DD> 284 Encodes the C++ and Java <CODE>int</CODE> types. 285 286 <DT><SAMP>`J'</SAMP> 287 <DD> 288 Indicates a complex type. 289 290 <DT><SAMP>`l'</SAMP> 291 <DD> 292 Encodes the C++ <CODE>long</CODE> type. 293 294 <DT><SAMP>`P'</SAMP> 295 <DD> 296 Indicates a pointer type. Followed by the type pointed to. 297 298 <DT><SAMP>`Q'</SAMP> 299 <DD> 300 Used to mangle qualified names, which arise from nested classes. 301 Should also be used for namespaces (?). 302 In Java used to mangle package-qualified names, and inner classes. 303 304 <DT><SAMP>`r'</SAMP> 305 <DD> 306 Encodes the GNU C++ <CODE>long double</CODE> type. 307 308 <DT><SAMP>`R'</SAMP> 309 <DD> 310 Indicates a reference type. Followed by the referenced type. 311 312 <DT><SAMP>`s'</SAMP> 313 <DD> 314 Encodes the C++ and java <CODE>short</CODE> types. 315 316 <DT><SAMP>`S'</SAMP> 317 <DD> 318 A modifier that indicates that the following integer type is signed. 319 Only used with <CODE>char</CODE>. 320 321 Also used as a modifier to indicate a static member function. 322 323 <DT><SAMP>`t'</SAMP> 324 <DD> 325 Indicates a template instantiation. 326 327 <DT><SAMP>`T'</SAMP> 328 <DD> 329 A back reference to a previously seen type. 330 331 <DT><SAMP>`U'</SAMP> 332 <DD> 333 A modifier that indicates that the following integer type is unsigned. 334 Also used to indicate that the following class or namespace name 335 is encoded using Unicode-mangling. 336 337 <DT><SAMP>`v'</SAMP> 338 <DD> 339 Encodes the C++ and Java <CODE>void</CODE> types. 340 341 <DT><SAMP>`V'</SAMP> 342 <DD> 343 A modified for a <CODE>const</CODE> type or method. 344 345 <DT><SAMP>`w'</SAMP> 346 <DD> 347 Encodes the C++ <CODE>wchar_t</CODE> type, and the Java <CODE>char</CODE> types. 348 349 <DT><SAMP>`x'</SAMP> 350 <DD> 351 Encodes the GNU C++ <CODE>long long</CODE> type, and the Java <CODE>long</CODE> type. 352 353 <DT><SAMP>`X'</SAMP> 354 <DD> 355 Encodes a template type parameter, when part of a function type. 356 357 <DT><SAMP>`Y'</SAMP> 358 <DD> 359 Encodes a template constant parameter, when part of a function type. 360 361 <DT><SAMP>`Z'</SAMP> 362 <DD> 363 Used for template type parameters. 364 365 </DL> 366 367 <P> 368 The letters <SAMP>`G'</SAMP>, <SAMP>`M'</SAMP>, <SAMP>`O'</SAMP>, and <SAMP>`p'</SAMP> 369 also seem to be used for obscure purposes ... 370 371 </P> 372 <P><HR><P> 373 Go to the <A HREF="gxxint_1.html">first</A>, <A HREF="gxxint_14.html">previous</A>, <A HREF="gxxint_16.html">next</A>, <A HREF="gxxint_16.html">last</A> section, <A HREF="gxxint_toc.html">table of contents</A>. 374 </BODY> 375 </HTML>