linux-kernel - Re: [RFC PATCH 7/7] sound: core: Avoid using timespec for struct snd_timer

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Date:   Fri, 22 Sep 2017 11:00:58 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        Takashi Sakamoto <o-takashi@...amocchi.jp>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>,
        Dan Carpenter <dan.carpenter@...cle.com>, jeeja.kp@...el.com,
        Vinod Koul <vinod.koul@...el.com>, dharageswari.r@...el.com,
        guneshwor.o.singh@...el.com, Bhumika Goyal <bhumirks@...il.com>,
        gudishax.kranthikumar@...el.com, Naveen M <naveen.m@...el.com>,
        hardik.t.shah@...el.com, Arvind Yadav <arvind.yadav.cs@...il.com>,
        Fabian Frederick <fabf@...net.be>,
        Mark Brown <broonie@...nel.org>,
        Deepa Dinamani <deepa.kernel@...il.com>,
        alsa-devel@...a-project.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 7/7] sound: core: Avoid using timespec for struct snd_timer_tread

On 21 September 2017 at 21:09, Arnd Bergmann <arnd@...db.de> wrote:
> On Thu, Sep 21, 2017 at 8:18 AM, Baolin Wang <baolin.wang@...aro.org> wrote:
>
>> +static int snd_timer_user_tread(void __user *argp, struct snd_timer_user *tu,
>> +                               unsigned int cmd)
>> +{
>> +       int __user *p = argp;
>> +       int xarg, old_tread;
>> +
>> +       if (tu->timeri) /* too late */
>> +               return -EBUSY;
>> +       if (get_user(xarg, p))
>> +               return -EFAULT;
>> +
>> +       old_tread = tu->tread;
>> +#if __BITS_PER_LONG == 64
>> +       tu->tread = xarg ? 2 : 0;
>> +#ifdef IA32_EMULATION
>> +       tu->tread = xarg ? 3 : 0;
>> +#endif
>> +#else
>> +       if (cmd == SNDRV_TIMER_IOCTL_TREAD64)
>> +               tu->tread = xarg ? 2 : 0;
>> +       else
>> +               tu->tread = xarg ? 1 : 0;
>> +#endif
>
> The 64-bit case looks broken here:
>
> - The tread flag is different for compat and native mode, so you
>    must pass a flag to identify whether you are called from
>    __snd_timer_user_ioctl or from snd_timer_user_ioctl_compat().

I have some confusion here. For 64-bit, we will set tu->tread = 2 no
matter it is native mode or compat mode, only we will set tu->tread =
3 for x86_32 in compat mode, right?
So I think we do not need to identify whether called from native mode
or compat mode.

>
> - On x86, you have to check whether calling user space process uses
>    the i386 or the x32 ABI by checking in_x32_syscall()

Make sense.

-- 
Baolin.wang
Best Regards