linux-kernel - [PATCH v2] ANDROID: binder: remove 32-bit binder interface.

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Message-Id: <20180511084524.234119-1-maco@android.com>
Date:   Fri, 11 May 2018 01:45:24 -0700
From:   Martijn Coenen <maco@...roid.com>
To:     john.stultz@...aro.org, tkjos@...gle.com, arve@...roid.com,
        amit.pundir@...aro.org, arnd@...db.de, gregkh@...uxfoundation.org
Cc:     linux-kernel@...r.kernel.org, devel@...verdev.osuosl.org,
        maco@...gle.com, Martijn Coenen <maco@...roid.com>
Subject: [PATCH v2] ANDROID: binder: remove 32-bit binder interface.

From: Martijn Coenen <maco@...gle.com>

New devices launching with Android P need to use the 64-bit
binder interface, even on 32-bit SoCs [0].

This change removes the Kconfig option to select the 32-bit
binder interface. We don't think this will affect existing
userspace for the following reasons:
1) The latest Android common tree is 4.14, so we don't
   believe any Android devices are on kernels >4.14.
2) Android devices launch on an LTS release and stick with
   it, so we wouldn't expect devices running on <= 4.14 now
   to upgrade to 4.17 or later. But even if they did, they'd
   rebuild the world (kernel + userspace) anyway.
3) Other userspaces like 'anbox' are already using the
   64-bit interface.

Note that this change doesn't remove the 32-bit UAPI
itself; the reason for that is that Android userspace
always uses the latest UAPI headers from upstream, and
userspace retains 32-bit support for devices that are
upgrading. This will be removed as well in 2-3 years,
at which point we can remove the code from the UAPI
as well.

Finally, this change introduces build errors on archs where
64-bit get_user/put_user is not supported, so make binder
unavailable on m68k (which wouldn't want it anyway).

[0]: https://android-review.googlesource.com/c/platform/build/+/595193

Signed-off-by: Martijn Coenen <maco@...roid.com>
---
Changes in v2:
  - Dropped support for m68k to avoid build errors.

 drivers/android/Kconfig  | 15 +--------------
 drivers/android/binder.c |  4 ----
 2 files changed, 1 insertion(+), 18 deletions(-)

diff --git a/drivers/android/Kconfig b/drivers/android/Kconfig
index 7dce3795b887..ee4880bfdcdc 100644
--- a/drivers/android/Kconfig
+++ b/drivers/android/Kconfig
@@ -10,7 +10,7 @@ if ANDROID

 config ANDROID_BINDER_IPC
 	bool "Android Binder IPC Driver"
-	depends on MMU
+	depends on MMU && !M68K
 	default n
 	---help---
 	  Binder is used in Android for both communication between processes,
@@ -32,19 +32,6 @@ config ANDROID_BINDER_DEVICES
 	  created. Each binder device has its own context manager, and is
 	  therefore logically separated from the other devices.

-config ANDROID_BINDER_IPC_32BIT
-	bool "Use old (Android 4.4 and earlier) 32-bit binder API"
-	depends on !64BIT && ANDROID_BINDER_IPC
-	default y
-	---help---
-	  The Binder API has been changed to support both 32 and 64bit
-	  applications in a mixed environment.
-
-	  Enable this to support an old 32-bit Android user-space (v4.4 and
-	  earlier).
-
-	  Note that enabling this will break newer Android user-space.
-
 config ANDROID_BINDER_IPC_SELFTEST
 	bool "Android Binder IPC Driver Selftest"
 	depends on ANDROID_BINDER_IPC
diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index e578eee31589..2ee9fb02dfb8 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -72,10 +72,6 @@
 #include <linux/security.h>
 #include <linux/spinlock.h>

-#ifdef CONFIG_ANDROID_BINDER_IPC_32BIT
-#define BINDER_IPC_32BIT 1
-#endif
-
 #include <uapi/linux/android/binder.h>
 #include "binder_alloc.h"
 #include "binder_trace.h"
-- 
2.17.0.441.gb46fe60e1d-goog