linux-kernel - Re: [PATCH 1/9] kernel: add a PF_FORCE

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Date:   Sun, 20 Sep 2020 00:24:11 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jens Axboe <axboe@...nel.dk>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        linux-arm-kernel@...ts.infradead.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
        io-uring@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, netdev@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

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]