Run armv7 32 bit userspace on aarch64

[arnd@arndb.de (Arnd Bergmann)]

On Friday 09 October 2015 17:28:08 Shi, Yang wrote:
> On 10/9/2015 3:32 PM, Shi, Yang wrote:
> > On 10/8/2015 4:12 AM, Will Deacon wrote:
> >> On Wed, Oct 07, 2015 at 03:46:57PM -0700, Shi, Yang wrote:
> >>> I'm trying to run armv7 little endian userspace on qemu aarch64 with
> >>> 4.1.x
> >>> kernel. I was told by someone such usecase is valid and I have
> >>> CONFIG_COMPAT
> >>> enabled in my kernel.
> >>>
> >>> But, I ran into the below error. It looks the userspace application is
> >>> trying to write a readonly page. I got the similar failure on arm vfp
> >>> with
> >>> Linaro images (4.1 kernel) too.
> >>>
> >>> Did anyone have tried it recently?
> >>
> >> -rc4 seems to be working fine with Debian Jessie armhf on my Juno boards.
> >>
> >> Do you have a good way of reproducing this with a mainline kernel?
> >
> > It seems a qemu's bug. I can get both ubuntu and openembedded userspace
> > bootup on my LS2085 board with 4.1 kernel.
> 
> Some new findings pointed me to another direction.
> 
> I just tried to build OE userspace with gcc 5.2 (default toolchain in OE 
> now), it fails to boot up with the same error.
> 
> Then I tried the below test on 4.1 kernel:
> 
> Linaro OE userspace image (4.9 toolchain)       Failed
> My OE build with 4.9.3 toolchain                Success
> My OE build with 5.2 toolchain                  Failed
> Ubuntu image                                    Success

Does your kernel have 64KB pages enabled? If it does, most 32-bit user space
won't run, except when building it with relatively new toolchains.

Try running with the default 4KB page size if that is the problem.

	Arnd