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

[Eugene Syromiatnikov]

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.
 * 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.

Thank you.