Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size

From: Arnd Bergmann
Date: Wed Mar 11 2015 - 08:47:56 EST

On Wednesday 11 March 2015 06:24:16 Alexander Graf wrote:
> So after recompiling all of the distribution with newer binutils we now
> have an openSUSE Factory tree that has 64k aligned 32bit binaries.
> Unfortunately however, the 32bit glibc has a bogus mmap() implementation
> that hard codes 4k page size.
> With the patch below applied to glibc, I can successfully run 32bit user
> space on Seattle with 64k PAGE_SIZE though. So I guess we'll need to fix
> up glibc next.
> Do you know of anyone who's fluent enough in 32bit ARM assembly to
> convert the hard coded assumptions in there to instead use a variable
> that takes the actual host page size into account?

I believe this is a kernel bug, and the kernel API for 32-bit emulation
should always take the pgoff argument in 4KB units instead of PAGE_SIZE
units, see the implementation of sys_mmap2 in

All user space programs that call mmap2 still need to make sure that
their arguments are PAGE_SIZE aligned, but the libc need not care
about this here.

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