Discussion and development of the “Itanium” portable C++ ABI used by many major C++ implementations. – Itanium C++ ABI. The Itanium ABI (which GCC uses) may specify these things (as within specifying ranges) Most types’ size and alignment is specified in the Intel System V ABI. Virtual Table Layout General A virtual table (vtable) is a table of information used to dispatch virtual functions, to ac.

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The types are substantively different ktanium B is a morally virtual base of D or if B is not located at offset zero in D.

Name mangling – Wikipedia

Each class has its own table that maps selectors to their implementations — the implementation pointer specifies where in memory the actual implementation of the method resides. To ensure that the virtual table pointers are set to the appropriate virtual tables during proper base class construction, a table of virtual table pointers, called the VTT, which holds the addresses of construction and non-construction virtual tables is generated for the complete class.

Such a class has no associated virtual table, and an object of such a class contains no virtual pointer. Please improve it by verifying the claims made and adding inline citations. When compiled, each method is named according to the following scheme for class methods:. Revise inheritance graph order definition.

The offset-to-top fields refer to B and B’s in particular will therefore be zero. Stack Overflow works best with JavaScript enabled. A function pointer a pointer to a function descriptor on Abj. In the special case where the parameter type has a non-trivial copy constructor or destructor, the caller must allocate space for a temporary copy, and pass the resulting copy by reference below. The type is omitted for variables and static data members.

The operators are encoded using their usual encoding a two-letter code in most cases. Pointer-to-member types encode the class and member types. The components and their meanings are as follows: A nonlocal scope is encoded as the qualifier of a qualified name: Update proposed object construction priority API 3.

This implies that the type information must keep a description of the public, unambiguous ifanium relationship of a type, as well as the const and volatile qualifications applied to types.

In particular, if the derived itanjum overrides a base agi virtual function with a different covariant return type, the entry for the derived class comes after the primary base’s embedded virtual table in declaration order, and is the entry used for calls from the derived class without adjustment. Other ABI aspects like exception handlingvirtual table layout, itanoum and stack frame paddingetc. Type bool has size and alignment 1. Email Required, but never shown.


The virtual base classes are neither empty nor nearly empty. The secondary virtual table for a base class B has the same contents as the primary virtual table for B, except that: You need to follow the documentation to the standards incorporated by reference.

The array cc and the cookie are all aligned naturally. There is no standard specification of whether the restrict attribute is part of the type for overloading purposes.

Tokens are placed in parentheses ” ” for grouping purposes. Sign up using Facebook. The discriminator is used only if there is more than one, for the second and subsequent ones.

Name mangling

Fix member function pointer description no division by two. RTTI queries in the base class constructor will return the type of itaniim base class, and virtual calls will resolve to member functions of the base class rather than the complete class. This includes class type parameters passed wholly or partially in registers. See the separate table summarizing the encoding characters used as terminals.

For each data component D first the primary base of C, if any, then the non-primary, non-virtual direct base classes in declaration order, then the non-static data members and unnamed bitfields in declaration orderallocate as follows: Even though its name is unique, g is still mangled: The virtual table contains a function pointer pointing to the non-adjusting entry point for A:: If virtual base A has a primary virtual base class P sharing its virtual table, P’s vbase and vcall offsets come first in the primary virtual table, in the same order they would appear if P itself were the virtual base, and those from A that do not replicate those from P precede them.

The virtual pointers in the secondary VTTs and virtual VTTs are used for subobject construction, and may always point to special construction virtual tables laid out as described in the following subsections.

However, in the case of pointer types, directly or indirectly pointing to incomplete class types, a more complex comparison is required, described below with the RTTI layout of pointer types.


Note requirements for an implementation to prevent users from emitting invalid vtables for RTTI classes. V’s virtual table contains virtual base offsets for S, U, and T in reverse inheritance graph preorderwhere the vbase offset for T is for the virtual base of U, not for the non-virtual direct base of V.

When a virtual function is invoked via a virtual base, but has been overridden in a derived class, the overriding function first adds a fixed offset to adjust the this pointer to the virtual base, and then adds the value contained at the vcall offset in the virtual base to its this pointer to get the address of the derived object where the function was overridden.

However, an implementation intending to support automatically thread-safe, one-time initialization as opposed to requiring explicit user control for thread safety may make use of the following API functions: A header file named cxxabi. This ABI does not require an implementation to support this capability, but it specifies such a facility for those implementations that do.

This virtual table is the primary virtual table of the class and is addressed by the virtual table pointer at the top of the object, which is not shared because there are no nearly empty virtual bases to be primary.

The return value is a pointer to a null-terminated array of characters, the demangled name. Therefore, any cross-references within the RTTI to types not known to be complete must be weak symbol references.

Itanium C++ ABI

No node is visited more than once. Any object code produced by compilers is usually linked with other pieces of object code produced by the same or another compiler by a type of program called a linker.

It returns zero if registration is successful, nonzero on failure. This entry point must load the vcall offset itxnium to f located in the virtual table for V obtained via its this pointer, extract the vcall offset corresponding to f located in that virtual table, and add this offset to the this pointer.

A component is earlier in the substitution dictionary than the structure of which it is a part.