# Linux Kernel Module Cheat

### 26.10. libc choice

Buildroot supports several libc implementations, including:

- glibc

- uClibc

We currently use glibc, which is selected by:

    BR2_TOOLCHAIN_BUILDROOT_GLIBC=y

Ideally we would like to use uClibc, as it is more minimal and easier to understand, but unfortunately there are some very few packages that use some weird glibc extension that uClibc hasn’t implemented yet, e.g.:

- SELinux. Trivial unmerged fix at: http://lists.busybox.net/pipermail/buildroot/2017-July/197793.html just missing the uClibc option to expose `fts.h`…​

- stress

The full list of unsupported packages can be found by grepping the Buildroot source:

    git -C "$(./getvar buildroot_source_dir)" grep 'depends on BR2_TOOLCHAIN_USES_GLIBC'

One "downside" of glibc is that it exercises much more kernel functionality on its more bloated pre-main init, which breaks user mode C hello worlds more often, see: Section 11.4, “User mode simulation with glibc”. I quote "downside" because glibc is actually exposing emulator bugs which we should actually go and fix.