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

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Date:	Tue, 18 Feb 2014 12:32:39 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Serban Constantinescu <serban.constantinescu@....com>,
	Colin Cross <ccross@...roid.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [PATCH 12/14] staging: binder: Fix ABI for 64bit Android

On Tue, Feb 18, 2014 at 12:02:07PM -0800, John Stultz wrote:
> On Tue, Feb 18, 2014 at 11:49 AM, Greg KH <gregkh@...uxfoundation.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@...uxfoundation.org> wrote:
> >> > On Mon, Feb 17, 2014 at 01:58:40PM -0800, John Stultz wrote:
> >> >> From: Serban Constantinescu <serban.constantinescu@....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.

But you added a field to the existing structure, right?  I don't really
remember the patch, it was a few hundred back in my review of stuff
today, sorry...

greg k-h
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