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        Philipp Tomsich <philipp.tomsich@theobroma-systems.com>,
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        Ramana Radhakrishnan <ramana.gcc@googlemail.com>,
        Steve Ellcey <sellcey@caviumnetworks.com>,
        Pavel Machek <pavel@ucw.cz>,
        Palmer Dabbelt <palmer@sifive.com>,
        Wookey <wookey@wookware.org>
Subject: Re: [PATCH v9 00/24] ILP32 for ARM64
To:     Eugene Syromiatnikov <esyr@redhat.com>,
        Yury Norov <ynorov@caviumnetworks.com>
References: <20180516081910.10067-1-ynorov@caviumnetworks.com>
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Date:   Wed, 10 Oct 2018 15:39:07 +0100
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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.