linux-kernel - Re: [PATCHv2 4/4] staging: android: ion: Add ioctl to query available heaps

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Message-ID: <f992a74b-7074-5e62-9f09-652ee4619fad@redhat.com>
Date:   Fri, 2 Sep 2016 14:27:21 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     kbuild test robot <lkp@...el.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     kbuild-all@...org, Sumit Semwal <sumit.semwal@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Riley Andrews <riandrews@...roid.com>,
        linaro-mm-sig@...ts.linaro.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org,
        Eun Taik Lee <eun.taik.lee@...sung.com>,
        Liviu Dudau <Liviu.Dudau@....com>,
        Jon Medhurst <tixy@...aro.org>,
        Mitchel Humpherys <mitchelh@...eaurora.org>,
        Jeremy Gebben <jgebben@...eaurora.org>,
        Bryan Huntsman <bryanh@...eaurora.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        Chen Feng <puck.chen@...ilicon.com>,
        Brian Starkey <brian.starkey@....com>
Subject: Re: [PATCHv2 4/4] staging: android: ion: Add ioctl to query available
 heaps

On 09/01/2016 04:44 PM, kbuild test robot wrote:
> Hi Laura,
>
> [auto build test WARNING on next-20160825]
> [cannot apply to staging/staging-testing v4.8-rc4 v4.8-rc3 v4.8-rc2 v4.8-rc4]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
> [Suggest to use git(>=2.9.0) format-patch --base=<commit> (or --base=auto for convenience) to record what (public, well-known) commit your patch series was built on]
> [Check https://git-scm.com/docs/git-format-patch for more information]
>
> url:    https://github.com/0day-ci/linux/commits/Laura-Abbott/staging-android-ion-Drop-heap-type-masks/20160902-071022
> config: mips-allyesconfig (attached as .config)
> compiler: mips-linux-gnu-gcc (Debian 5.4.0-6) 5.4.0 20160609
> reproduce:
>         wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         make.cross ARCH=mips
>
> All warnings (new ones prefixed by >>):
>
>    drivers/staging/android/ion/ion.c: In function 'ion_query_heaps':
>>> drivers/staging/android/ion/ion.c:1181:3: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
>       (struct ion_heap_data __user *)query->heaps;
>       ^
>

botching-up-ioctls.txt says:

  * Pointers are __u64, cast from/to a uintprt_t on the userspace side and
    from/to a void __user * in the kernel. Try really hard not to delay this
    conversion or worse, fiddle the raw __u64 through your code since that
    diminishes the checking tools like sparse can provide.

This doesn't seem like it will work on 32-bit systems since you'll end up
with the warning above. Is there a better option or did I misunderstand
how that is supposed to work?

Thanks,
Laura