If you try to compile code from embedded-handbook you'll receive a warning: warning: incompatible implicit declaration of built-in function 'memcpy' [enabled by default] It can be fixed if you replace "#include <unistd.h>" with "#include <string.h>"
http://sources.gentoo.org/gentoo/xml/htdocs/proj/en/base/embedded/handbook/cross-qemu.xml?r1=1.4&r2=1.5