Google developed a custom library for the C compiler (libc) called Bionic. This was necessary for three main reasons:
- License: they wanted to keep GPL out of user-space. Bionic code uses the BSD license.
- Size: the library has to be loaded in each process, so it needs to be small. Bionic is about 200K, or half the size of glibc (the GNU version of libc).
- Speed: limited CPU power means it needs to be fast. Bionic has a small size and fast code paths, including a very fast and small custom pthread implementation.