> We had a useful discussion about C++11 ABI issues at the GNU Tools
> Cauldron (http://gcc.gnu.org/wiki/cauldron2012). The approach will be
> shaped over time, but the general idea is as follows.
>
> We will modify g++ to support a type attribute indicating the version
> of the type, as a string. This type attribute will be inherited by
> any other type that uses it, as a class/struct member or via
> inheritance. Type attributes will be concatenated as needed. This
> type attribute will then be used in the mangled name of any function
> that takes a parameter of a type with an attribute or returns a type
> with an attribute. The type attribute will also be used in the
> mangled name of any global variable whose type has an attribute.
I (finally) managed to dig up some memories on this topic. Here's a
rough summary of how it works on HP-UX:
We added one new Gnu-style attribute:
__attribute_((version_id("version_identifier")))
This attribute can be attached to a typedef, struct/union/class,
function, or variable declaration, or to function and variable
definitions. If a variable is redeclared in the same source file, its
version identifier must match in both declarations.
Normally, the version identifier is applied to a type. It then
propagates to any declaration using that type, whether it's another
type or function or variable. For struct/union/class types, if any
member or base class has an attached version identifier (excluding
static data members, static member functions, and non-virtual member
functions), we attach the version identifier to the enclosing type. If
there is more than one, we use the lexically greater identifier. For
arrays, pointer and reference types, and typedefs, the version
identifier propagates from the base type to the derived type. For
pointer-to-member, if either the base class or the base type has a
version identifier, the new type gets it.
For global variables, if the type has a version identifier, the linker
name of the variable gets decorated as
"source_name{version_identifier}". For functions, if the return type
or any of the formal parameter types have version identifiers, the
linker name of the function gets decorated the same way. Non-static
member functions will also inherit the version identifier of the base
class (because of the implicit "this" parameter).
If a variable or function gets a version identifier applied to it
directly, but also inherits one from its type, we use the lexically
greater.
-cary
