Re: [PATCH 12/14] staging: binder: Fix ABI for 64bit Android

John Stultz
2014-02-18T20:02:10Z

On Tue, Feb 18, 2014 at 11:49 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> On Tue, Feb 18, 2014 at 11:30:26AM -0800, John Stultz wrote:
>> On Tue, Feb 18, 2014 at 11:08 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> > On Mon, Feb 17, 2014 at 01:58:40PM -0800, John Stultz wrote:
>> >> From: Serban Constantinescu <serban.constantinescu@arm.com>
>> >>
>> >> This patch fixes the ABI for 64bit Android userspace.
>> >> BC_REQUEST_DEATH_NOTIFICATION and BC_CLEAR_DEATH_NOTIFICATION claim
>> >> to be using struct binder_ptr_cookie, but they are using a 32bit handle
>> >> and a pointer.
>> >>
>> >> On 32bit systems the payload size is the same as the size of struct
>> >> binder_ptr_cookie, however for 64bit systems this will differ. This
>> >> patch adds struct binder_handle_cookie that fixes this issue for 64bit
>> >> Android.
>> >>
>> >> Since there are no 64bit users of this interface that we know of this
>> >> change should not affect any existing systems.
>> >
>> > But you are changing the ioctl structures here, what is that going to
>> > cause with old programs?
>>
>> So I'd be glad for Serban or Arve to clarify, but my understanding
>> (and as is described in the commit message) is that the assumption is
>> there are no 64bit binder users at this point, and the ioctl structure
>> changes are made such that existing 32bit applications are unaffected.
>
> How does changing the structure size, and contents, not affect any
> applications or the kernel code? What am I missing here?

On 32bit pointers and ints are the same size? (Years ago I sat through
your presentation on this, so I'm worried I'm missing something here
:)

struct binder_ptr_cookie {
void *ptr;
void *cookie;
};

struct binder_handle_cookie {
__u32 handle;
void *cookie;
} __attribute__((packed));

On 32bit systems these are the same size. Now on 64bit systems, this
changes things, and would break users, but the assumption here is
there are no pre-existing 64bit binder users.

>> >> Cc: Colin Cross <ccross@android.com>
>> >> Cc: Arve Hjønnevåg <arve@android.com>
>> >> Cc: Serban Constantinescu <serban.constantinescu@arm.com>
>> >> Cc: Android Kernel Team <kernel-team@android.com>
>> >
>> > I am going to require Acks from someone on the Android team to accept
>> > this, or any other 64bit binder patch, given all the back-and-forth that
>> > has happened with the different patch sets here over the past year or
>> > so.
>>
>> Certainly reasonable given the earlier back and forth. For extra
>> context, these have been merged into the 3.10 AOSP by Arve:
>> https://android-review.googlesource.com/#/c/79228/
>
> That's good to see, and a good reason to get them merged, but better
> descriptions and acks would be nice to have :)
>
> How about sending these as a separate series when all worked out, as
> lots of people seem interested in them?

Yep. Will do.

thanks
-john