gxxint.texi

gcc-2.95.3 Linux下最常用的C编译器

GNU Java does the same.

@subsection Primitive types

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

The C++ and Java floating-point types @code{float} and @code{double}
are mangled as @samp{f} and @samp{d} respectively.

The C++ @code{bool} type and the Java @code{boolean} type are
mangled as @samp{b}.

The C++ @code{wchar_t} and the Java @code{char} types are
mangled as @samp{w}.

The Java integral types @code{byte}, @code{short}, @code{int}
and @code{long} are mangled as @samp{c}, @samp{s}, @samp{i},
and @samp{x}, respectively.

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

@subsection 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 @code{Foo}
is encoded as @samp{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 @samp{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 @samp{U}.

For example, the method @code{X\u0319::M\u002B(int)} is encoded as
@samp{M_002b__U6X_0319iU}.


@subsection Pointer and reference types

A C++ pointer type is mangled as @samp{P} followed by the
mangling of the type pointed to.

A C++ reference type as mangled as @samp{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 @samp{P} followed by the mangling of the class name.

@subsection Squangled type compression

Squangling (enabled with the @samp{-fsquangle} option), utilizes the
@samp{B} code to indicate reuse of a previously seen type within an
indentifier. Types are recognized in a left to right manner and given
increasing values, which are appended to the code in the standard
manner. Ie, multiple digit numbers are delimited by @samp{_}
characters. A type is considered to be any non primitive type,
regardless of whether its a parameter, template parameter, or entire
template. Certain codes are considered modifiers of a type, and are not
included as part of the type. These are the @samp{C}, @samp{V},
@samp{P}, @samp{A}, @samp{R}, @samp{U} and @samp{u} codes, denoting
constant, volatile, pointer, array, reference, unsigned, and restrict.
These codes may precede a @samp{B} type in order to make the required
modifications to the type.

For example:
@example
template <class T> class class1 @{ @};

template <class T> class class2 @{ @};

class class3 @{ @};

int f(class2<class1<class3> > a ,int b, const class1<class3>&c, class3 *d) @{ @}

    B0 -> class2<class1<class3>
    B1 -> class1<class3>
    B2 -> class3
@end example
Produces the mangled name @samp{f__FGt6class21Zt6class11Z6class3iRCB1PB2}.
The int parameter is a basic type, and does not receive a B encoding...

@subsection 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 @samp{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 @code{Foo::\u0319::Bar} is encoded as
@samp{Q33FooU5_03193Bar}.

Squangling utilizes the the letter @samp{K} to indicate a 
remembered portion of a qualified name. As qualified names are processed
for an identifier, the names are numbered and remembered in a 
manner similar to the @samp{B} type compression code. 
Names are recognized left to right, and given increasing values, which are
appended to the code in the standard manner. ie, multiple digit numbers
are delimited by @samp{_} characters.

For example 
@example
class Andrew 
@{
  class WasHere 
  @{
      class AndHereToo 
      @{
      @};
  @};
@};

f(Andrew&r1, Andrew::WasHere& r2, Andrew::WasHere::AndHereToo& r3) @{ @}

   K0 ->  Andrew
   K1 ->  Andrew::WasHere
   K2 ->  Andrew::WasHere::AndHereToo
@end example
Function @samp{f()} would be mangled as : 
@samp{f__FR6AndrewRQ2K07WasHereRQ2K110AndHereToo}

There are some occasions when either a @samp{B} or @samp{K} code could
be chosen, preference is always given to the @samp{B} code. Ie, the example
in the section on @samp{B} mangling could have used a @samp{K} code 
instead of @samp{B2}.

@subsection Templates

A class template instantiation is encoded as the letter @samp{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 @samp{Z} followed by the encoding of the type.

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

@subsection Arrays

C++ array types are mangled by emitting @samp{A}, followed by
the length of the array, followed by an @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.

Java arrays are objects.  A Java type @code{T[]} is mangled
as if it were the C++ type @code{JArray<T>}.
For example @code{java.lang.String[]} is encoded as
@samp{Pt6JArray1ZPQ34java4lang6String}.

@subsection Static fields

Both C++ and Java classes can have static fields.
These are allocated statically, and are shared among all instances.

The mangling starts with a prefix (@samp{_} in most systems), which is
followed by the mangling
of the class name, followed by the "joiner" and finally the field name.
The joiner (see @code{JOINER} in @code{cp-tree.h}) is a special
separator character.  For historical reasons (and idiosyncracies
of assembler syntax) it can @samp{$} or @samp{.} (or even
@samp{_} on a few systems).  If the joiner is @samp{_} then the prefix
is @samp{__static_} instead of just @samp{_}.

For example @code{Foo::Bar::var} (or @code{Foo.Bar.var} in Java syntax)
would be encoded as @samp{_Q23Foo3Bar$var} or @samp{_Q23Foo3Bar.var}
(or rarely @samp{__static_Q23Foo3Bar_var}).

If the name of a static variable needs Unicode escapes,
the Unicode indicator @samp{U} comes before the "joiner".
This @code{\u1234Foo::var\u3445} becomes @code{_U8_1234FooU.var_3445}.

@subsection Table of demangling code characters

The following special characters are used in mangling:

@table @samp
@item A
Indicates a C++ array type.

@item b
Encodes the C++ @code{bool} type,
and the Java @code{boolean} type.

@item B
Used for squangling. Similar in concept to the 'T' non-squangled code.

@item c
Encodes the C++ @code{char} type, and the Java @code{byte} type.

@item C
A modifier to indicate a @code{const} type.
Also used to indicate a @code{const} member function
(in which cases it precedes the encoding of the method's class).

@item d
Encodes the C++ and Java @code{double} types.

@item e
Indicates extra unknown arguments @code{...}.

@item E
Indicates the opening parenthesis of an expression.

@item f
Encodes the C++ and Java @code{float} types.

@item F
Used to indicate a function type.

@item H
Used to indicate a template function.

@item i
Encodes the C++ and Java @code{int} types.

@item I
Encodes typedef names of the form @code{int@var{n}_t}, where @var{n} is a
positive decimal number.  The @samp{I} is followed by either two
hexidecimal digits, which encode the value of @var{n}, or by an
arbitrary number of hexidecimal digits between underscores.  For
example, @samp{I40} encodes the type @code{int64_t}, and @samp{I_200_}
encodes the type @code{int512_t}.

@item J
Indicates a complex type.

@item K
Used by squangling to compress qualified names.

@item l
Encodes the C++ @code{long} type.

@item n
Immediate repeated type. Followed by the repeat count.

@item N 
Repeated type. Followed by the repeat count of the repeated type,
followed by the type index of the repeated type. Due to a bug in
g++ 2.7.2, this is only generated if index is 0. Superceded by
@samp{n} when squangling.

@item P
Indicates a pointer type.  Followed by the type pointed to.

@item Q
Used to mangle qualified names, which arise from nested classes.
Also used for namespaces.
In Java used to mangle package-qualified names, and inner classes.

@item r
Encodes the GNU C++ @code{long double} type.

@item R
Indicates a reference type.  Followed by the referenced type.

@item s
Encodes the C++ and java @code{short} types.

@item S
A modifier that indicates that the following integer type is signed.
Only used with @code{char}.

Also used as a modifier to indicate a static member function.

@item t
Indicates a template instantiation.

@item T
A back reference to a previously seen type.

@item 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.

@item u
The @code{restrict} type qualifier.

@item v
Encodes the C++ and Java @code{void} types.

@item V
A modifier for a @code{volatile} type or method.

@item w
Encodes the C++ @code{wchar_t} type, and the Java @code{char} types.

@item W
Indicates the closing parenthesis of an expression.

@item x
Encodes the GNU C++ @code{long long} type, and the Java @code{long} type.

@item X
Encodes a template type parameter, when part of a function type.

@item Y
Encodes a template constant parameter, when part of a function type.

@item Z
Used for template type parameters. 

@end table

The letters @samp{G}, @samp{M}, @samp{O}, and @samp{p}
also seem to be used for obscure purposes ...

@node Vtables, Concept Index, Mangling, Top
@section Virtual Tables

In order to invoke virtual functions, GNU C++ uses virtual tables. Each
virtual function gets an index, and the table entry points to the
overridden function to call. Sometimes, and adjustment to the this
pointer has to be made before calling a virtual function:

@example
struct A@{
  int i;
  virtual void foo();
@};

struct B@{
  int j;
  virtual void bar();
@};

struct C:A,B@{
  virtual void bar();
@};

void C::bar()
@{
  i++;
@}

int main()
@{
  C *c = new C;
  B *b = c;
  c->bar();
@}
@end exam