mailing list of musl libc
 help / color / mirror / code / Atom feed
From: Arnd Bergmann <arnd@arndb.de>
To: musl@lists.openwall.com
Cc: Rich Felker <dalias@libc.org>, Arnd Bergmann <arnd@arndb.de>,
	Michael Forney <mforney@mforney.org>,
	 ALSA Development Mailing List <alsa-devel@alsa-project.org>,
	Takashi Iwai <tiwai@suse.com>,
	 Baolin Wang <baolin.wang@linaro.org>,
	y2038 Mailman List <y2038@lists.linaro.org>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Mark Brown <broonie@kernel.org>,
	 Baolin Wang <baolin.wang7@gmail.com>
Subject: Re: [musl] Re: [alsa-devel] [PATCH v7 8/9] ALSA: add new 32-bit layout for snd_pcm_mmap_status/control
Date: Fri, 8 Oct 2021 11:24:39 +0200	[thread overview]
Message-ID: <CAK8P3a0qxNLv3_RcR5COcRGPcTnYMcfbOjdWKiT2hKdcof9WUg@mail.gmail.com> (raw)
In-Reply-To: <s5h5yu79aab.wl-tiwai@suse.de>

On Fri, Oct 8, 2021 at 10:43 AM Takashi Iwai <tiwai@suse.de> wrote:
> On Thu, 07 Oct 2021 18:51:58 +0200, Rich Felker wrote:
> > On Thu, Oct 07, 2021 at 06:18:52PM +0200, Takashi Iwai wrote:
>
> @@ -557,11 +558,15 @@ struct __snd_pcm_sync_ptr {
>  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __BIG_ENDIAN : defined(__BIG_ENDIAN)
>  typedef char __pad_before_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
>  typedef char __pad_after_uframe[0];
> +typedef char __pad_before_u32[4];
> +typedef char __pad_after_u32[0];
>  #endif
>
>  #if defined(__BYTE_ORDER) ? __BYTE_ORDER == __LITTLE_ENDIAN : defined(__LITTLE_ENDIAN)
>  typedef char __pad_before_uframe[0];
>  typedef char __pad_after_uframe[sizeof(__u64) - sizeof(snd_pcm_uframes_t)];
> +typedef char __pad_before_u32[0];
> +typedef char __pad_after_u32[4];
>  #endif

I think these should remain unchanged, the complex expression was intentionally
done so the structures are laid out the same way on 64-bit
architectures, so that
the kernel can use the __SND_STRUCT_TIME64 path internally on both 32-bit
and 64-bit architectures.

> @@ -2970,8 +2981,17 @@ static int snd_pcm_sync_ptr(struct snd_pcm_substream *substream,
>         memset(&sync_ptr, 0, sizeof(sync_ptr));
>         if (get_user(sync_ptr.flags, (unsigned __user *)&(_sync_ptr->flags)))
>                 return -EFAULT;
> -       if (copy_from_user(&sync_ptr.c.control, &(_sync_ptr->c.control), sizeof(struct snd_pcm_mmap_control)))
> -               return -EFAULT;
> +       if (buggy_control) {
> +               if (copy_from_user(&sync_ptr.c.control_api_2_0_15,
> +                                  &(_sync_ptr->c.control_api_2_0_15),
> +                                  sizeof(sync_ptr.c.control_api_2_0_15)))
> +                       return -EFAULT;
> +       } else {
> +               if (copy_from_user(&sync_ptr.c.control,
> +                                  &(_sync_ptr->c.control),
> +                                  sizeof(sync_ptr.c.control)))
> +                       return -EFAULT;
> +       }

The problem I see with this is that it might break musl's ability to
emulate the new
interface on top of the old (time32) one for linux-4.x and older
kernels, as the conversion
function is no longer stateless but has to know the negotiated
interface version.

It's probably fine as long as we can be sure that the 2.0.16+ API
version only gets
negotiated if both the kernel and user sides support it, and musl only emulates
the 2.0.15 API version from the current kernels.

I've tried to understand this part of musl's convert_ioctl_struct(), but I just
can't figure out whether it does the conversion based the on the layout that
is currently used in the kernel, or based on the layout we should have been
using, and would use with the above fix. Rich, can you help me here?

       Arnd

  parent reply	other threads:[~2021-10-08  9:25 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20191211212025.1981822-1-arnd@arndb.de>
     [not found] ` <20191211212025.1981822-9-arnd@arndb.de>
     [not found]   ` <29QBMJU8DE71E.2YZSH8IHT5HMH@mforney.org>
     [not found]     ` <s5hpmsh9kdx.wl-tiwai@suse.de>
     [not found]       ` <CAK8P3a0K3XtjiszC3XWgG0L8+AgO+xUGr_KEAnb9a5GmyecoUQ@mail.gmail.com>
     [not found]         ` <s5hee8x9f92.wl-tiwai@suse.de>
2021-10-07 13:11           ` Arnd Bergmann
2021-10-07 15:33             ` Takashi Iwai
2021-10-07 16:06               ` Rich Felker
2021-10-07 16:18                 ` Takashi Iwai
2021-10-07 16:51                   ` Rich Felker
2021-10-08  8:43                     ` Takashi Iwai
2021-10-08  8:44                       ` Takashi Iwai
2021-10-08  9:24                       ` Arnd Bergmann [this message]
2021-10-08 11:11                         ` Takashi Iwai
2021-10-08 11:45                           ` Arnd Bergmann
2021-10-08 11:53                             ` Takashi Iwai
2021-10-08 12:13                               ` Arnd Bergmann
2021-10-08 12:07                           ` Rich Felker
2021-10-10  7:53                             ` Takashi Iwai
2021-10-18 14:43                               ` Rich Felker
2021-10-18 14:58                                 ` Takashi Iwai
2021-10-18 15:08                                   ` Rich Felker
2021-10-18 15:26                                     ` Arnd Bergmann
2021-10-18 20:42                                       ` Rich Felker
2021-10-19 14:16                                         ` Rich Felker
2021-10-19 14:23                                           ` Arnd Bergmann
2021-10-08 12:06                         ` Rich Felker
2021-10-08 12:37                           ` Arnd Bergmann
2021-10-08 17:20                             ` Rich Felker

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAK8P3a0qxNLv3_RcR5COcRGPcTnYMcfbOjdWKiT2hKdcof9WUg@mail.gmail.com \
    --to=arnd@arndb.de \
    --cc=alsa-devel@alsa-project.org \
    --cc=baolin.wang7@gmail.com \
    --cc=baolin.wang@linaro.org \
    --cc=broonie@kernel.org \
    --cc=dalias@libc.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mforney@mforney.org \
    --cc=musl@lists.openwall.com \
    --cc=tiwai@suse.com \
    --cc=y2038@lists.linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this public inbox

	https://git.vuxu.org/mirror/musl/

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).