linux-kernel - Re: [PATCH] ANDROID: binder: remove 32-bit binder interface.

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Date:   Mon, 14 May 2018 05:03:38 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Martijn Coenen <maco@...roid.com>
Cc:     kbuild test robot <lkp@...el.com>,
        Greg KH <gregkh@...uxfoundation.org>, kbuild-all@...org,
        John Stultz <john.stultz@...aro.org>,
        Todd Kjos <tkjos@...gle.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Amit Pundir <amit.pundir@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        Martijn Coenen <maco@...gle.com>, geert@...ux-m68k.org,
        linux-m68k@...ts.linux-m68k.org
Subject: Re: [PATCH] ANDROID: binder: remove 32-bit binder interface.

On Fri, May 11, 2018 at 09:57:52AM +0200, Martijn Coenen wrote:
> On Sat, May 5, 2018 at 2:10 PM, kbuild test robot <lkp@...el.com> wrote:
> >    drivers/android/binder.o: In function `binder_thread_write':
> >>> binder.c:(.text+0x6a16): undefined reference to `__get_user_bad'
> 
> Looks like m68k doesn't support 64-bit get_user(). I could just have
> binder depend on !CONFIG_M68K, but there may be other architectures
> still that don't support this. Another alternative would be to
> whitelist the architectures Android supports - eg arm, arm64, x86,
> x86_64. But I'm not sure if arch-limited drivers are considered bad
> form. Does anybody have suggestions for how to deal with this?

The proper fix is to just support 640bit get/put_user on m68k instead
of working around this.