These are the GNU binutils. These are utilities of use when dealing with binary files, either object files or executables. These tools consist of the linker (ld), the assembler (gas), and the profiler (gprof) each of which have their own sub-directory named after them. There is also a collection of other binary tools, including the disassembler (objdump) in this directory. These tools make use of a pair of libraries (bfd and opcodes) and a common set of header files (include).