[Arm-dev] Chrooting/Docker to armv7hl and armv5tel on aarch64

[Gordan Bobic]

Figured it out. Two kernel configuration options were in play:

CONFIG_COMPAT=y
CONFIG_LSM_MMAP_MIN_ADDR=32768

Above is what is required to run armv5tel and armv7hl chroots on aarch64.
Default for the latter option is 65535, which prevents 32-bit binaries from
running. Up and running with 4.9.153 now.

I hope this is useful to someone else.

On Sat, Jan 26, 2019 at 8:08 PM Gordan Bobic <gordan at redsleeve.org> wrote:

> I did a bit more digging, and rebuilding 4.9.153 with CONFIG_COMPAT and a
> few related options, had an effect - no longer do I get "exec format error"
> - now it just outright segfaults.
> 4.4.172 works perfectly.
>
> I'm using clean mainline kernels with no additional patches.
>
> chrooting to aarch64 chroots works.
>
>
> On Sat, Jan 26, 2019 at 6:07 PM Stephen John Smoogen <smooge at gmail.com>
> wrote:
>
>>
>>
>> On Sat, 26 Jan 2019 at 18:45, Gordan Bobic <gordan at redsleeve.org> wrote:
>>
>>> Yes, they are "wrong", but not "WRONG!".
>>>
>>> As I (possibly poorly) explained, I'm running on an aarch64 machine, but
>>> am trying to run armv5tel and armv7hl chroots.
>>> I just dug out an old kernel I was using (4.4.72) and I can now chroot
>>> just fine.
>>>
>>> So it's something that changed in the kernel, but I'm not sure what else
>>> it could be other than the page size (which I already checked).
>>>
>>> I'm going to build the latest 4.4.172 with my 4.4.72 config and see if
>>> that works. If it does, I'll try to make oldconfig that on 4.9.153 and try
>>> again, see if that breaks things again. I was just hoping there might be an
>>> option I missed in 4.9 that enables/disables downward compatibility.
>>>
>>>
>> The places I have seen where  this breaks before was
>> * it works on only specific  aarch64 devices
>> * it works but only after you update the firmware to a newer vendor
>> version (because the kernel expects that to fix something else)
>> * it is a regression and needs to be fixed.
>>
>> [The first one was where someone remembered it working but forgot they
>> were  working on XYZ box and then replicated in ABC and found the arch
>> didn't have that.]
>>
>> I am expecting it is going to be 3... but I would check on 2 also.
>>
>>
>>
>>> Gordan
>>>
>>> On Sat, Jan 26, 2019 at 5:41 PM Stephan GUILLOUX <
>>> stephan.guilloux at free.fr> wrote:
>>>
>>>> Wrong architecture binaries, in the chroot'ed folder ?
>>>>
>>>> What do you get with:
>>>>
>>>>      file <chroot>/bin/bash
>>>>
>>>> On 26-Jan-19 17:49, Gordan Bobic wrote:
>>>> > It's been so long since I last had to do this, that it looks like a
>>>> > kernel update somewhere along the way broke this for me. :-(
>>>> >
>>>> > What happens now:
>>>> >
>>>> > # chroot rs7
>>>> > chroot: failed to run command ‘/bin/bash’: Exec format error
>>>> >
>>>> > I could have sworn that this was all I needed to make this work last
>>>> time:
>>>> > # grep 4K_PAGES config-4.9.153-1.el7.centos.aarch64
>>>> > CONFIG_ARM64_4K_PAGES=y
>>>> > # CONFIG_ARM64_64K_PAGES is not set
>>>> >
>>>> > Unfortunately, now trying to chroot into either hard-float or
>>>> > soft-float chroot results in the exec format error.
>>>> >
>>>> > Looking at time stamps of various things, I had this working with
>>>> > 4.4.70, but have since switched to 4.9.x kernels. Any thoughts on
>>>> what
>>>> > changed between 4.4 and 4.9 would be most appreciated.
>>>> >
>>>> > What am I missing?
>>>> >
>>>> > _______________________________________________
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>>
>>
>> --
>> Stephen J Smoogen.
>>
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>
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