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Date:   Sun, 20 Sep 2020 00:24:11 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Andy Lutomirski <luto@amacapital.net>
Cc:     Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
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        keyrings@vger.kernel.org, linux-security-module@vger.kernel.org
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
Message-ID: <20200919232411.GK3421308@ZenIV.linux.org.uk>
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On Sat, Sep 19, 2020 at 03:53:40PM -0700, Andy Lutomirski wrote:

> > It would not be a win - most of the syscalls don't give a damn
> > about 32bit vs. 64bit...
> 
> Any reasonable implementation would optimize it out for syscalls that don’t care.  Or it could be explicit:
> 
> DEFINE_MULTIARCH_SYSCALL(...)

1) what would that look like?
2) have you counted the syscalls that do and do not need that?
3) how many of those realistically *can* be unified with their
compat counterparts?  [hint: ioctl(2) cannot]