Constructors
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Classes in C++ have 'constructors' and 'destructors'.  These are functions which are called automatically by the language whenever data of a class is created or destroyed.  Class data which is static data may also be have a type which requires 'construction', the contructor must be called before the data can be referenced, so the contructor must be called before the program begins. The common solution to this problem is for the compiler to call a magic function as the first statement main. This magic function, (often called __main) runs around calling the constructors for all the things needing it. With COFF the compile has a bargain with the linker et al. All constructors are given strange names, for example __GLOBAL__$I$foo might be the label of a contructor for the class FOO.  The solution on unfortunate systems (most system V machines) is to perform a partial link on all the .o files, do an nm on the result, run awk or some such over the result looking for strange __GLOBAL__$ symbols, generate a C program from this, compile it and link with the partially linked input. This process is usually called collect. Some versions of a.out use something called the set_vector mechanism.  The constructor symbols are output from the compiler with a special stab code saying that they are constructors, and the linker can deal with them directly. BFD allows applications (ie the linker) to deal with constructor information independently of their external implimentation by providing a set of entry points for the indiviual object back ends to call which maintains a database of the contructor information.  The application can interrogate the database to find out what it wants.  The construction data essential for the linker to be able to perform its job are:

  * asymbol The asymbol of the contructor entry point contains all the information necessary to call the function. table id The type of symbol, ie is it a contructor, a destructor or something else someone dreamed up to make our lives difficult. This module takes this information and then builds extra sections attached to the bfds which own the entry points.  It creates these sections as if they were tables of pointers to the entry points, and builds relocation entries to go with them so that the tables can be relocated along with the data they reference. These sections are marked with a special bit (SEC_CONSTRUCTOR) which the linker notices and do with what it wants.

bfd_constructor_entry
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Synopsis

     void bfd_constructor_entry(bfd *abfd,
         asymbol **symbol_ptr_ptr,
         CONST char*type);

Description

This function is called with an a symbol describing the function to be called, an string which descibes the xtor type, eg something like "CTOR" or "DTOR" would be fine. And the bfd which owns the function. Its duty is to create a section called "CTOR" or "DTOR" or whatever if the bfd doesn't already have one, and grow a relocation table for the entry points as they accumulate.