G++ internals - Mangling

From c8661ffad4c2bbf1dd9138c4e8de7d86396cd070 Mon Sep 17 00:00:00 2001 From: rsc Date: Tue, 29 Nov 2005 04:05:50 +0000 Subject: demangling docs --- src/libmach/gxxint_15.html | 375 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 375 insertions(+) create mode 100644 src/libmach/gxxint_15.html (limited to 'src/libmach/gxxint_15.html') diff --git a/src/libmach/gxxint_15.html b/src/libmach/gxxint_15.html new file mode 100644 index 00000000..cdee7dda --- /dev/null +++ b/src/libmach/gxxint_15.html @@ -0,0 +1,375 @@ + + + + +G++ internals - Mangling + + +Go to the first, previous, next, last section, table of contents. +

+ + +

Function name mangling for C++ and Java

+ +

+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 name mangling. The inverse +process is called demangling. + +

+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. + +

+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). + +

+ + +

Method name mangling

+ +

+C++ mangles a method by emitting the function name, followed by __, +followed by encodings of any method qualifiers (such as const), +followed by the mangling of the method's class, +followed by the mangling of the parameters, in order. + +

+For example Foo::bar(int, long) const is mangled +as `bar__C3Fooil'. + +

+For a constructor, the method name is left out. +That is Foo::Foo(int, long) const is mangled +as `__C3Fooil'. + +

+GNU Java does the same. + +

+ + +

Primitive types

+ +

+The C++ types int, long, short, char, +and long long are mangled as `i', `l', +`s', `c', and `x', respectively. +The corresponding unsigned types have `U' prefixed +to the mangling. The type signed char is mangled `Sc'. + +

+The C++ and Java floating-point types float and double +are mangled as `f' and `d' respectively. + +

+The C++ bool type and the Java boolean type are +mangled as `b'. + +

+The C++ wchar_t and the Java char types are +mangled as `w'. + +

+The Java integral types byte, short, int +and long are mangled as `c', `s', `i', +and `x', respectively. + +

+C++ code that has included javatypes.h will mangle +the typedefs jbyte, jshort, jint +and jlong as respectively `c', `s', `i', +and `x'. (This has not been implemented yet.) + +

+ + +

Mangling of simple names

+ +

+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 Foo +is encoded as `3Foo'. + +

+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 `U' 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. + +

+If a method name contains Unicode-escaped characters, the +entire mangled method name is followed by a `U'. + +

+For example, the method X\u0319::M\u002B(int) is encoded as +`M_002b__U6X_0319iU'. + +

+ + +

Pointer and reference types

+ +

+A C++ pointer type is mangled as `P' followed by the +mangling of the type pointed to. + +

+A C++ reference type as mangled as `R' followed by the +mangling of the type referenced. + +

+A Java object reference type is equivalent +to a C++ pointer parameter, so we mangle such an parameter type +as `P' followed by the mangling of the class name. + +

+ + +

Qualified names

+ +

+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. + +

+These are all mangled the same way: First the letter `Q' +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. + +

+For example Foo::\u0319::Bar is encoded as +`Q33FooU5_03193Bar'. + +

+ + +

Templates

+ +

+A class template instantiation is encoded as the letter `t', +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 `Z' followed by the encoding of the type. + +

+A function template specialization (either an instantiation or an +explicit specialization) is encoded by an `H' followed by the +encoding of the template parameters, as described above, followed by +an `_', the encoding of the argument types template function (not the +specialization), another `_', 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 `X' for type parameters, or a +`Y' for constant parameters, and an index indicating their position +in the template parameter list declaration. + +

+ + +

Arrays

+ +

+C++ array types are mangled by emitting `A', followed by +the length of the array, followed by an `_', 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. + +

+Java arrays are objects. A Java type T[] is mangled +as if it were the C++ type JArray<T>. +For example java.lang.String[] is encoded as +`Pt6JArray1ZPQ34java4lang6String'. + +

+ + +

Table of demangling code characters

+ +

+The following special characters are used in mangling: + +

`A' +: +Indicates a C++ array type. + +
`b' +: +Encodes the C++ bool type, +and the Java boolean type. + +
`c' +: +Encodes the C++ char type, and the Java byte type. + +
`C' +: +A modifier to indicate a const type. +Also used to indicate a const member function +(in which cases it precedes the encoding of the method's class). + +
`d' +: +Encodes the C++ and Java double types. + +
`e' +: +Indicates extra unknown arguments .... + +
`f' +: +Encodes the C++ and Java float types. + +
`F' +: +Used to indicate a function type. + +
`H' +: +Used to indicate a template function. + +
`i' +: +Encodes the C++ and Java int types. + +
`J' +: +Indicates a complex type. + +
`l' +: +Encodes the C++ long type. + +
`P' +: +Indicates a pointer type. Followed by the type pointed to. + +
`Q' +: +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. + +
`r' +: +Encodes the GNU C++ long double type. + +
`R' +: +Indicates a reference type. Followed by the referenced type. + +
`s' +: +Encodes the C++ and java short types. + +
`S' +: +A modifier that indicates that the following integer type is signed. +Only used with char. + +Also used as a modifier to indicate a static member function. + +
`t' +: +Indicates a template instantiation. + +
`T' +: +A back reference to a previously seen type. + +
`U' +: +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. + +
`v' +: +Encodes the C++ and Java void types. + +
`V' +: +A modified for a const type or method. + +
`w' +: +Encodes the C++ wchar_t type, and the Java char types. + +
`x' +: +Encodes the GNU C++ long long type, and the Java long type. + +
`X' +: +Encodes a template type parameter, when part of a function type. + +
`Y' +: +Encodes a template constant parameter, when part of a function type. + +
`Z' +: +Used for template type parameters. + +

+ +

+The letters `G', `M', `O', and `p' +also seem to be used for obscure purposes ... + +

+Go to the first, previous, next, last section, table of contents. + + -- cgit v1.2.3