The Kindles have a relatively old version of (soft float) glibc installed.
It is possible to run more than one version of glibc, including one that lives outside of /lib (say, in: */extensions/system/lib) on a Linux system.
See the overview here:
https://bitbucket.org/twobob/kual-system
I.E: If you need a (modern) hard float libc for your Kindle applications.
Overview (including how to build for a non-/lib path):
http://stackoverflow.com/questions/8...-a-single-host
The tool for editing the related fields in an ELF binary:
http://nixos.org/patchelf.html
(Nit: watch out, that option is "--dynamic-linker" with two (2) leading "--")
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I am adding this post, because usually a "custom kernel" is not the final goal of most posters.