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

From: Szabolcs Nagy
Date: Wed Oct 10 2018 - 10:39:39 EST

On 10/10/18 15:10, Eugene Syromiatnikov wrote:
> * 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.

but that's necessarily the case for all ilp32 abis:
the userspace syscall function receives 32bit
arguments so even if the kernel abi takes 64bit
args you cannot use that from c code. (the libc
does not even know which args should be sign or
zero extended.)

process_vm_readv/writev is limited by the ilp32
iovec struct, not by the syscall arguments.

ptrace is specified to take void* addr argument,
and void* is 32bit on all ilp32 targets.
so again on the c language level there is no
way around the 32bit limitation.