I just stumbled over the MAP_UNINITIALIZED defintion, initially added by: commit ea637639591def87a54cea811cbac796980cb30d Author: Jie Zhang <jie.zhang@xxxxxxxxxx> Date: Mon Dec 14 18:00:02 2009 -0800 nommu: fix malloc performance by adding uninitialized flag The defintion depends on CONFIG_MMAP_ALLOW_UNINITIALIZED, which will never be set by userspace. How is this supposed to work? Shoudn't we define the symbol unconditionally and just turn it into a no-op in the implementation? There are a few similar issues, like struct elf_prstatus having a different layout depending on CONFIG_BINFMT_ELF_FDPIC, or MAX_SHARED_LIBS defending on CONFIG_BINFMT_SHARED_FLAT.