The Cygnus libraries, which include the C library, libc, and the math library, libm.
 

The C++ library developed by Cygnus.

libgloss

libgloss, the library for GNU Low-level OS Support, contains the startup code, the I/O support for gcc and newlib (the C library), and the target board support packages to which you need to port the GNU tools for an embedded execution target.
The C library used throughout this documentation is newlib; however, libgloss could easily be made to support other C libraries. Because libgloss resides in its own tree, it’s able to run standalone, allowing it to support GDB’s remote debugging and to be included in other GNU tools. Several functions that are essential to gcc reside in libgloss. These include the following functions.