The Binary File Descriptor library (BFD) is the GNU Project's main mechanism for the portable manipulation of s in a variety of s. , it supports approximately 50 file formats for some 25 instruction set architectures.
When David Henkel-Wallace of Cygnus Support proposed developing the library as a way to open up new business opportunities for the company, Richard Stallman said that it would be difficult; David's response was that it wasn't such a "Big Fucking Deal". Abbreviated to "BFD", this became the library name. "Binary File Descriptor" was invented later as a backronym for "BFD".
BFD works by presenting a common abstract view of object files. An object file has a "header" with descriptive info; a variable number of "sections" that each has a name, some attributes, and a block of data; a symbol table; relocation entries; and so forth.
Internally, BFD translates the data from the abstract view into the details of the bit/byte layout required by the target processor and file format. Its key services include handling byte order differences, such as between a little-endian host and big-endian target, correct conversion between 32-bit and 64-bit data, and details of address arithmetic specified by relocation entries.
BFD library can be logically divided into two parts. The front-end and the back-end. The front-end gives a common interface independent of underlying object file view. Users will be interacting with the object files with this interface. Even if the layout of the object files are not to known the user, user still be able to use the interface. This hiding of the detail is done with the help of the back-end. The back-end implements how the front-end interface interacts with the object files layout. Whenever a new object files type is introduced the back-end needs to register the type and implement it if it needs to be supported by the BFD application.
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Relocation is the process of assigning load addresses for position-dependent code and data of a program and adjusting the code and data to reflect the assigned addresses. Prior to the advent of multiprocess systems, and still in many embedded systems, the addresses for objects were absolute starting at a known location, often zero. Since multiprocessing systems dynamically link and switch between programs it became necessary to be able to relocate objects using position-independent code.