linux-kernel - Re: [PATCH V9 21/21] csky: support dword access for get_user

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Message-ID: <CAK8P3a1wfeWboHvU1o_kooMc2hML8iWcNrz=mp6tYT52iGwfjw@mail.gmail.com>
Date:   Wed, 17 Oct 2018 17:44:17 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Guo Ren <ren_guo@...ky.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        David Miller <davem@...emloft.net>,
        gregkh <gregkh@...uxfoundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rob Herring <robh@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>, c-sky_gcc_upstream@...ky.com
Subject: Re: [PATCH V9 21/21] csky: support dword access for get_user_size()

On Tue, Oct 16, 2018 at 5:33 AM Guo Ren <ren_guo@...ky.com> wrote:
>
> Support dword access for get_user_size and redesign put_user_size with
> the same style of get_user_size. It's Ok to use xxx_user_asm_common for
> all size of variable with ldb, ldh, ldw, ld.d
>
> ld.d rx, (addr, 0) could "rx <= addr" "and r(x+1) <= addr+4" and this also
> follow abiv2 gcc ABI for dword access.

Are you sure this is correct for this?

static inline u32 get_64_to_32(__u64 __user *p)
{
      u32 ret;
      get_user(ret, p);
      return ret;
}

If I read __get_user_asm_common() right, the ld.d would overwrite
two registers, but the caller only expects one, so it clobbers one
that might be in use.

     Arnd