Re: [PATCH v4 00/24] ILP32 for ARM64

Arnd Bergmann
2015-04-14T22:28:56Z

On Tuesday 14 April 2015 16:00:34 Catalin Marinas wrote:
> On Tue, Apr 14, 2015 at 04:07:36PM +0200, Arnd Bergmann wrote:
> > For completeness, there is yet another option, which would be to use the
> > exact system call table from arm64 and do all the emulation in user space
> > rather than the kernel. This would however be the least compatible with
> > existing source code, so you probably don't want to do that.
>
> It would be great if this worked but I think we looked at it before and
> it seems nice until you hit the futex stuff and robust lists (I don't
> fully remember the details). Some of the structures (siginfo) would no
> longer be POSIX compliant and some of them aren't only accessed via libc
> to be able to create shadow copies.

Well, that may or may not be acceptable. Aarch64-ilp32 mode is a hack to
enable a very special class of applications, it's not like anyone would
want to run a full system for this and need POSIX compliance.

We could definitely be pragmatic and do whatever helps get the job
done. That said, it diverges further from what legacy 32-bit applications
expect to see, so this approach will likely make an application port harder,
not easier.

Arnd