Re: [PATCH v9 00/24] ILP32 for ARM64

[Arnd Bergmann]

On 10/10/18, Eugene Syromiatnikov <esyr@xxxxxxxxxx> wrote:
> On Tue, Jul 24, 2018 at 08:39:57PM +0300, Yury Norov wrote:
>> Hi all,
>>
>> + Pavel Machek, Palmer Dabbelt, Wookey.
>>
>> On Wed, May 16, 2018 at 11:18:45AM +0300, Yury Norov wrote:
>> > This series enables AARCH64 with ILP32 mode.
>> >
>> > As supporting work, it introduces ARCH_32BIT_OFF_T configuration
>> > option that is enabled for existing 32-bit architectures but disabled
>> > for new arches (so 64-bit off_t userspace type is used by new
>> > userspace).
>> > Also it deprecates getrlimit and setrlimit syscalls prior to prlimit64.
>> >
>> > Based on kernel v4.16. Tested with LTP, glibc testsuite, trinity,
>> > lmbench,
>> > CPUSpec.
>
>> This is the update of the series based on 4.17 kernel
>> https://github.com/norov/linux/tree/ilp32-4.17
>
> Hello.
>
> I have some questions regarding AArch64 ILP32 implementation for which I
> failed to find an answer myself:
>  * How ptrace() tracer is supposed to distinguish between ILP32 and LP64
>    tracees? For MIPS N32 and x32 this is possible based on syscall
>    number, but for AArch64 ILP32 I do not see such a sign. There's also
>    ARM_ip is employed for signalling entering/exiting, I wonder whether
>    it's possible to employ it also for signalling tracee's personality.

Don't know.

>  * What's the reasoning behind capping syscall arguments to 32 bit? x32
>    and MIPS N32 do not have such a restriction (and do not need special
>    wrappers for syscalls that pass 64-bit values as a result, except
>    when they do,  as it is the case for preadv2 on x32); moreover, that
>    would lead to insurmountable difficulties for AArch64 ILP32 tracers
>    that try to trace LP64 tracees, as it would be impossible to pass
>    64-bit addresses to process_vm_{read,write} or ptrace PEEK/POKE.

The idea is to keep the syscall entry points as similar as possible
between arm (aarch32) emulation and aarch64-ilp32 mode when
you have a kernel that supports both.

      Arnd