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Date:   Sat, 19 Sep 2020 17:14:41 -0700
From:   Andy Lutomirski <>
To:     Al Viro <>
Cc:     Christoph Hellwig <>,
        Andrew Morton <>,
        Jens Axboe <>, Arnd Bergmann <>,
        David Howells <>,
        linux-arm-kernel <>,
        X86 ML <>, LKML <>,
        "open list:MIPS" <>,
        Parisc List <>,
        linuxppc-dev <>,
        linux-s390 <>,
        sparclinux <>,
        linux-block <>,
        Linux SCSI List <>,
        Linux FS Devel <>,,,
        linux-arch <>,
        Linux-MM <>,
        Network Development <>,,
        LSM List <>
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag

On Sat, Sep 19, 2020 at 4:24 PM Al Viro <> wrote:
> 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:
> >
> 1) what would that look like?

In effect, it would work like this:

/* Arch-specific, but there's a generic case for sane architectures. */
enum syscall_arch {

  args are the args here, and arch is the arch.

> 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]

There would be no requirement to unify anything.  The idea is that
we'd get rid of all the global state flags.

For ioctl, we'd have a new file_operation:

long ioctl(struct file *, unsigned int, unsigned long, enum syscall_arch);

I'm not saying this is easy, but I think it's possible and the result
would be more obviously correct than what we have now.

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