Arnd Bergmann <arnd@xxxxxxxx> wrote: > > 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? Yes. > Right, good catch. That should work. It can probably be done > by adding another check before the conditional, like: > > /* clear anonymous mappings that don't ask for uninitialized data */ > if (!vma->vm_file && > !(IS_ENABLED(CONFIG_MMAP_ALLOW_UNINITIALIZED) && > (flags & MAP_UNINITIALIZED)) > memset((void *)region->vm_start, 0, > region->vm_end - region->vm_start); Sounds good. > > 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. Because the kernel code uses that header and that struct too, so you'd break compilation of binfmt_elf_fdpic.c. There is a way round it - and that's to copy the struct into the non-UAPI backing header and delete the conditional section from the UAPI one. You'd have to stop the non-UAPI header from #including the UAPI header, though, and you'd have to hope that no one is trying to set it in userspace (gdb doesn't). David
