x32 ABI for 64-bit mode

configname: CONFIG_X86_X32

Linux Kernel Configuration
└─>Executable file formats / Emulations
└─>x32 ABI for 64-bit mode
In linux kernel since version 3.1 (release Date: 2011-10-24)  
Include code to run binaries for the x32 native 32-bit ABI
for 64-bit processors. An x32 process gets access to the
full 64-bit register file and wide data path while leaving
pointers at 32 bits for smaller memory footprint.

You will need a recent binutils (2.22 or later) with
elf32_x86_64 support enabled to compile a kernel with this
option set.