linux-kernel - linux-next: build failure after merge of the aio tree

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Date:	Tue, 15 Mar 2016 17:46:34 +1100
From:	Stephen Rothwell <sfr@...b.auug.org.au>
To:	Benjamin LaHaise <bcrl@...ck.org>
Cc:	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	<linuxppc-dev@...ts.ozlabs.org>, Al Viro <viro@...IV.linux.org.uk>,
	Christoph Hellwig <hch@....de>
Subject: linux-next: build failure after merge of the aio tree

Hi Benjamin,

After merging the aio tree, today's linux-next build (powerpc
ppc44x_defconfig) failed like this:

fs/built-in.o: In function `aio_thread_op_foo_at':
aio.c:(.text+0x4dab4): undefined reference to `__get_user_bad'
aio.c:(.text+0x4daec): undefined reference to `__get_user_bad'

Caused by commit

  150a0b4905f1 ("aio: add support for async openat()")

despite commit

  d2f7a973e11e ("aio: don't use __get_user() for 64 bit values")

This is due to a bug in the powerpc __get_user_check() macro (the return
value is defined to be "unsigned long" which is only 32 bits on a 32
bit platform).

I applied the patch below which seems to help (Michael, what do you
think?), but given Al's and Christoph's reactions, I am inclined to
remove the aio tree from tomorrow and maybe it can be revisited after
the merge window.

From: Stephen Rothwell <sfr@...b.auug.org.au>
Date: Tue, 15 Mar 2016 16:36:06 +1100
Subject: [PATCH] powerpc: fix get_user for 64 bit typs on 32 bit platforms

solution borrowed from the x86 uaccess.h

Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
---
 arch/powerpc/include/asm/uaccess.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index b7c20f0b8fbe..52262b2f37fc 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -261,10 +261,13 @@ do {								\
 	}							\
 } while (0)
 
+#define __inttype(x) \
+	__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
+
 #define __get_user_nocheck(x, ptr, size)			\
 ({								\
 	long __gu_err;						\
-	unsigned long __gu_val;					\
+	__inttype(*(ptr)) __gu_val;				\
 	__typeof__(*(ptr)) __user *__gu_addr = (ptr);	\
 	__chk_user_ptr(ptr);					\
 	if (!is_kernel_addr((unsigned long)__gu_addr))		\
@@ -277,7 +280,7 @@ do {								\
 #define __get_user_check(x, ptr, size)					\
 ({									\
 	long __gu_err = -EFAULT;					\
-	unsigned long  __gu_val = 0;					\
+	__inttype(*(ptr)) __gu_val = 0;				\
 	__typeof__(*(ptr)) __user *__gu_addr = (ptr);		\
 	might_fault();							\
 	if (access_ok(VERIFY_READ, __gu_addr, (size)))			\
@@ -289,7 +292,7 @@ do {								\
 #define __get_user_nosleep(x, ptr, size)			\
 ({								\
 	long __gu_err;						\
-	unsigned long __gu_val;					\
+	__inttype(*(ptr)) __gu_val;				\
 	__typeof__(*(ptr)) __user *__gu_addr = (ptr);	\
 	__chk_user_ptr(ptr);					\
 	__get_user_size(__gu_val, __gu_addr, (size), __gu_err);	\
-- 
2.7.0

-- 
Cheers,
Stephen Rothwell