Re: [Qemu-devel] [PATCH v2 5/5] linux-user: Add aarch64_be magic numbers to qemu-binfmt-conf.sh

[Laurent Vivier <laurent@vivier.eu>]

Le 20/12/2017 à 17:15, Michael Weiser a écrit :
> Hi Laurent,
> 
> On Wed, Dec 20, 2017 at 04:56:41PM +0100, Laurent Vivier wrote:
> 
>>> Based on that I suspect that qemu-binfmt-conf.sh's current assignment of
>>> armeb and aarch64 into the arm CPU family is over-optimistic as well.
>>> So I'd suggest treating all of arm, armeb, aarch64 and aarch64_be as
>>> separate families.
>> So it's not like on intel/AMD where we can execute a 32bit binary on a
>> 64bit kernel?
> 
> An aarch64 CPU is capable of running arm (i.e. aarch32) code. And I
> think this is supported as a multilib setup on Linux. But not in mixed
> endianess as far as I know.
> 
> Looking at the code again, I'm confused now: Wouldn't the current logic
> treat an actual i386 machine as capable of running x86_64 binaries
> natively and omit registering the handler for x86_64?

It can be read like that, but actually 32bit machine cannot emulate
64bit architecture, so we don't register it.

So for the same family:

- on 64bit machine, we don't register the interpreter because the 32bit
binary can be executed natively,

- on 32bit machine, we don't register the interpreter because the
interpreter cannot work,

Thanks,
Laurent