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| <TITLE>G++ internals - Mangling</TITLE> |
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| <H2><A NAME="SEC20" HREF="gxxint_toc.html#TOC20">Function name mangling for C++ and Java</A></H2> |
| |
| <P> |
| Both C++ and Jave provide overloaded function and methods, |
| which are methods with the same types but different parameter lists. |
| Selecting the correct version is done at compile time. |
| Though the overloaded functions have the same name in the source code, |
| they need to be translated into different assembler-level names, |
| since typical assemblers and linkers cannot handle overloading. |
| This process of encoding the parameter types with the method name |
| into a unique name is called <EM>name mangling</EM>. The inverse |
| process is called <EM>demangling</EM>. |
| |
| </P> |
| <P> |
| It is convenient that C++ and Java use compatible mangling schemes, |
| since the makes life easier for tools such as gdb, and it eases |
| integration between C++ and Java. |
| |
| </P> |
| <P> |
| Note there is also a standard "Jave Native Interface" (JNI) which |
| implements a different calling convention, and uses a different |
| mangling scheme. The JNI is a rather abstract ABI so Java can call methods |
| written in C or C++; |
| we are concerned here about a lower-level interface primarily |
| intended for methods written in Java, but that can also be used for C++ |
| (and less easily C). |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC21" HREF="gxxint_toc.html#TOC21">Method name mangling</A></H3> |
| |
| <P> |
| C++ mangles a method by emitting the function name, followed by <CODE>__</CODE>, |
| followed by encodings of any method qualifiers (such as <CODE>const</CODE>), |
| followed by the mangling of the method's class, |
| followed by the mangling of the parameters, in order. |
| |
| </P> |
| <P> |
| For example <CODE>Foo::bar(int, long) const</CODE> is mangled |
| as <SAMP>`bar__C3Fooil'</SAMP>. |
| |
| </P> |
| <P> |
| For a constructor, the method name is left out. |
| That is <CODE>Foo::Foo(int, long) const</CODE> is mangled |
| as <SAMP>`__C3Fooil'</SAMP>. |
| |
| </P> |
| <P> |
| GNU Java does the same. |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC22" HREF="gxxint_toc.html#TOC22">Primitive types</A></H3> |
| |
| <P> |
| The C++ types <CODE>int</CODE>, <CODE>long</CODE>, <CODE>short</CODE>, <CODE>char</CODE>, |
| and <CODE>long long</CODE> are mangled as <SAMP>`i'</SAMP>, <SAMP>`l'</SAMP>, |
| <SAMP>`s'</SAMP>, <SAMP>`c'</SAMP>, and <SAMP>`x'</SAMP>, respectively. |
| The corresponding unsigned types have <SAMP>`U'</SAMP> prefixed |
| to the mangling. The type <CODE>signed char</CODE> is mangled <SAMP>`Sc'</SAMP>. |
| |
| </P> |
| <P> |
| The C++ and Java floating-point types <CODE>float</CODE> and <CODE>double</CODE> |
| are mangled as <SAMP>`f'</SAMP> and <SAMP>`d'</SAMP> respectively. |
| |
| </P> |
| <P> |
| The C++ <CODE>bool</CODE> type and the Java <CODE>boolean</CODE> type are |
| mangled as <SAMP>`b'</SAMP>. |
| |
| </P> |
| <P> |
| The C++ <CODE>wchar_t</CODE> and the Java <CODE>char</CODE> types are |
| mangled as <SAMP>`w'</SAMP>. |
| |
| </P> |
| <P> |
| The Java integral types <CODE>byte</CODE>, <CODE>short</CODE>, <CODE>int</CODE> |
| and <CODE>long</CODE> are mangled as <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>, |
| and <SAMP>`x'</SAMP>, respectively. |
| |
| </P> |
| <P> |
| C++ code that has included <CODE>javatypes.h</CODE> will mangle |
| the typedefs <CODE>jbyte</CODE>, <CODE>jshort</CODE>, <CODE>jint</CODE> |
| and <CODE>jlong</CODE> as respectively <SAMP>`c'</SAMP>, <SAMP>`s'</SAMP>, <SAMP>`i'</SAMP>, |
| and <SAMP>`x'</SAMP>. (This has not been implemented yet.) |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC23" HREF="gxxint_toc.html#TOC23">Mangling of simple names</A></H3> |
| |
| <P> |
| A simple class, package, template, or namespace name is |
| encoded as the number of characters in the name, followed by |
| the actual characters. Thus the class <CODE>Foo</CODE> |
| is encoded as <SAMP>`3Foo'</SAMP>. |
| |
| </P> |
| <P> |
| If any of the characters in the name are not alphanumeric |
| (i.e not one of the standard ASCII letters, digits, or '_'), |
| or the initial character is a digit, then the name is |
| mangled as a sequence of encoded Unicode letters. |
| A Unicode encoding starts with a <SAMP>`U'</SAMP> to indicate |
| that Unicode escapes are used, followed by the number of |
| bytes used by the Unicode encoding, followed by the bytes |
| representing the encoding. ASSCI letters and |
| non-initial digits are encoded without change. However, all |
| other characters (including underscore and initial digits) are |
| translated into a sequence starting with an underscore, |
| followed by the big-endian 4-hex-digit lower-case encoding of the character. |
| |
| </P> |
| <P> |
| If a method name contains Unicode-escaped characters, the |
| entire mangled method name is followed by a <SAMP>`U'</SAMP>. |
| |
| </P> |
| <P> |
| For example, the method <CODE>X\u0319::M\u002B(int)</CODE> is encoded as |
| <SAMP>`M_002b__U6X_0319iU'</SAMP>. |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC24" HREF="gxxint_toc.html#TOC24">Pointer and reference types</A></H3> |
| |
| <P> |
| A C++ pointer type is mangled as <SAMP>`P'</SAMP> followed by the |
| mangling of the type pointed to. |
| |
| </P> |
| <P> |
| A C++ reference type as mangled as <SAMP>`R'</SAMP> followed by the |
| mangling of the type referenced. |
| |
| </P> |
| <P> |
| A Java object reference type is equivalent |
| to a C++ pointer parameter, so we mangle such an parameter type |
| as <SAMP>`P'</SAMP> followed by the mangling of the class name. |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC25" HREF="gxxint_toc.html#TOC25">Qualified names</A></H3> |
| |
| <P> |
| Both C++ and Java allow a class to be lexically nested inside another |
| class. C++ also supports namespaces (not yet implemented by G++). |
| Java also supports packages. |
| |
| </P> |
| <P> |
| These are all mangled the same way: First the letter <SAMP>`Q'</SAMP> |
| indicates that we are emitting a qualified name. |
| That is followed by the number of parts in the qualified name. |
| If that number is 9 or less, it is emitted with no delimiters. |
| Otherwise, an underscore is written before and after the count. |
| Then follows each part of the qualified name, as described above. |
| |
| </P> |
| <P> |
| For example <CODE>Foo::\u0319::Bar</CODE> is encoded as |
| <SAMP>`Q33FooU5_03193Bar'</SAMP>. |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC26" HREF="gxxint_toc.html#TOC26">Templates</A></H3> |
| |
| <P> |
| A class template instantiation is encoded as the letter <SAMP>`t'</SAMP>, |
| followed by the encoding of the template name, followed |
| the number of template parameters, followed by encoding of the template |
| parameters. If a template parameter is a type, it is written |
| as a <SAMP>`Z'</SAMP> followed by the encoding of the type. |
| |
| </P> |
| <P> |
| A function template specialization (either an instantiation or an |
| explicit specialization) is encoded by an <SAMP>`H'</SAMP> followed by the |
| encoding of the template parameters, as described above, followed by |
| an <SAMP>`_'</SAMP>, the encoding of the argument types template function (not the |
| specialization), another <SAMP>`_'</SAMP>, and the return type. (Like the |
| argument types, the return type is the return type of the function |
| template, not the specialization.) Template parameters in the argument |
| and return types are encoded by an <SAMP>`X'</SAMP> for type parameters, or a |
| <SAMP>`Y'</SAMP> for constant parameters, and an index indicating their position |
| in the template parameter list declaration. |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC27" HREF="gxxint_toc.html#TOC27">Arrays</A></H3> |
| |
| <P> |
| C++ array types are mangled by emitting <SAMP>`A'</SAMP>, followed by |
| the length of the array, followed by an <SAMP>`_'</SAMP>, followed by |
| the mangling of the element type. Of course, normally |
| array parameter types decay into a pointer types, so you |
| don't see this. |
| |
| </P> |
| <P> |
| Java arrays are objects. A Java type <CODE>T[]</CODE> is mangled |
| as if it were the C++ type <CODE>JArray<T></CODE>. |
| For example <CODE>java.lang.String[]</CODE> is encoded as |
| <SAMP>`Pt6JArray1ZPQ34java4lang6String'</SAMP>. |
| |
| </P> |
| |
| |
| <H3><A NAME="SEC28" HREF="gxxint_toc.html#TOC28">Table of demangling code characters</A></H3> |
| |
| <P> |
| The following special characters are used in mangling: |
| |
| </P> |
| <DL COMPACT> |
| |
| <DT><SAMP>`A'</SAMP> |
| <DD> |
| Indicates a C++ array type. |
| |
| <DT><SAMP>`b'</SAMP> |
| <DD> |
| Encodes the C++ <CODE>bool</CODE> type, |
| and the Java <CODE>boolean</CODE> type. |
| |
| <DT><SAMP>`c'</SAMP> |
| <DD> |
| Encodes the C++ <CODE>char</CODE> type, and the Java <CODE>byte</CODE> type. |
| |
| <DT><SAMP>`C'</SAMP> |
| <DD> |
| A modifier to indicate a <CODE>const</CODE> type. |
| Also used to indicate a <CODE>const</CODE> member function |
| (in which cases it precedes the encoding of the method's class). |
| |
| <DT><SAMP>`d'</SAMP> |
| <DD> |
| Encodes the C++ and Java <CODE>double</CODE> types. |
| |
| <DT><SAMP>`e'</SAMP> |
| <DD> |
| Indicates extra unknown arguments <CODE>...</CODE>. |
| |
| <DT><SAMP>`f'</SAMP> |
| <DD> |
| Encodes the C++ and Java <CODE>float</CODE> types. |
| |
| <DT><SAMP>`F'</SAMP> |
| <DD> |
| Used to indicate a function type. |
| |
| <DT><SAMP>`H'</SAMP> |
| <DD> |
| Used to indicate a template function. |
| |
| <DT><SAMP>`i'</SAMP> |
| <DD> |
| Encodes the C++ and Java <CODE>int</CODE> types. |
| |
| <DT><SAMP>`J'</SAMP> |
| <DD> |
| Indicates a complex type. |
| |
| <DT><SAMP>`l'</SAMP> |
| <DD> |
| Encodes the C++ <CODE>long</CODE> type. |
| |
| <DT><SAMP>`P'</SAMP> |
| <DD> |
| Indicates a pointer type. Followed by the type pointed to. |
| |
| <DT><SAMP>`Q'</SAMP> |
| <DD> |
| Used to mangle qualified names, which arise from nested classes. |
| Should also be used for namespaces (?). |
| In Java used to mangle package-qualified names, and inner classes. |
| |
| <DT><SAMP>`r'</SAMP> |
| <DD> |
| Encodes the GNU C++ <CODE>long double</CODE> type. |
| |
| <DT><SAMP>`R'</SAMP> |
| <DD> |
| Indicates a reference type. Followed by the referenced type. |
| |
| <DT><SAMP>`s'</SAMP> |
| <DD> |
| Encodes the C++ and java <CODE>short</CODE> types. |
| |
| <DT><SAMP>`S'</SAMP> |
| <DD> |
| A modifier that indicates that the following integer type is signed. |
| Only used with <CODE>char</CODE>. |
| |
| Also used as a modifier to indicate a static member function. |
| |
| <DT><SAMP>`t'</SAMP> |
| <DD> |
| Indicates a template instantiation. |
| |
| <DT><SAMP>`T'</SAMP> |
| <DD> |
| A back reference to a previously seen type. |
| |
| <DT><SAMP>`U'</SAMP> |
| <DD> |
| A modifier that indicates that the following integer type is unsigned. |
| Also used to indicate that the following class or namespace name |
| is encoded using Unicode-mangling. |
| |
| <DT><SAMP>`v'</SAMP> |
| <DD> |
| Encodes the C++ and Java <CODE>void</CODE> types. |
| |
| <DT><SAMP>`V'</SAMP> |
| <DD> |
| A modified for a <CODE>const</CODE> type or method. |
| |
| <DT><SAMP>`w'</SAMP> |
| <DD> |
| Encodes the C++ <CODE>wchar_t</CODE> type, and the Java <CODE>char</CODE> types. |
| |
| <DT><SAMP>`x'</SAMP> |
| <DD> |
| Encodes the GNU C++ <CODE>long long</CODE> type, and the Java <CODE>long</CODE> type. |
| |
| <DT><SAMP>`X'</SAMP> |
| <DD> |
| Encodes a template type parameter, when part of a function type. |
| |
| <DT><SAMP>`Y'</SAMP> |
| <DD> |
| Encodes a template constant parameter, when part of a function type. |
| |
| <DT><SAMP>`Z'</SAMP> |
| <DD> |
| Used for template type parameters. |
| |
| </DL> |
| |
| <P> |
| The letters <SAMP>`G'</SAMP>, <SAMP>`M'</SAMP>, <SAMP>`O'</SAMP>, and <SAMP>`p'</SAMP> |
| also seem to be used for obscure purposes ... |
| |
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