Buildroot's coreutils uname(1) command has a special patch applied as part of buildroot. When you run 'uname -p', it tries to print out extended information about the processor you are running. It does this by parsing /proc/cpuinfo. I'm not sure of the provenance of this enhancement, but you can read the code in package/coreutils/coreutils-uname.patch. However, on recent ARM kernels, the format of /proc/cpuinfo has changed incompatibly. Several packages subsequently break. I believe the commit in question is this: http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=82b5df7bf27ca6cf642499bc3bcae1c93b9ac4ba So, I recently discovered that when matched with recent ARM kernels, uname -p on buildroot is simply reporting 'Unknown'. I'm not really sure what the right answer might be. The code doesn't really seem set up to parse the /proc/cpuinfo file in more than one way. I am presently using buildroot 2012.11, but the code seems to be the same in the latest release as well.
This really is a coreutils upstream problem. Could you report this directly to the coreutils developers? On Buildroot side, I believe we should drop coreutils-uname.patch since it's really a feature patch, and it apparently has no chance of making its way to the upstream. Another option is to look for an updated version of this patch somewhere.