Untitled Document: How It Works

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### 1.2 How To Use BFD

To use the library, include `bfd.h` and link with `libbfd.a`.

BFD provides a common interface to the parts of an object file for a calling application.

When an application successfully opens a target file (object, archive, or whatever), a pointer to an internal structure is returned. This pointer points to a structure called `bfd`, described in `bfd.h`. Our convention is to call this pointer a BFD, and instances of it within code `abfd`. All operations on the target object file are applied as methods to the BFD. The mapping is defined within `bfd.h` in a set of macros, all beginning with ‘`bfd_`’ to reduce namespace pollution.

For example, this sequence does what you would probably expect: return the number of sections in an object file attached to a BFD `abfd`.

    #include "bfd.h"

    unsigned int number_of_sections (abfd)
    bfd *abfd;
    {
      return bfd_count_sections (abfd);
    }

The abstraction used within BFD is that an object file has:

- a header,
- a number of sections containing raw data (see Sections),
- a set of relocations (see Relocations), and
- some symbol information (see Symbols).

Also, BFDs opened for archives have the additional attribute of an index and contain subordinate BFDs. This approach is fine for a.out and coff, but loses efficiency when applied to formats such as S-records and IEEE-695.