linux-kernel - [PATCH 3.16 013/305] ARM: fix put

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Message-ID: <lsq.1549201508.687968953@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Bernd Edlinger" <bernd.edlinger@...mail.de>,
        "Arnd Bergmann" <arnd@...db.de>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Johannes Pointner" <h4nn35.work@...il.com>
Subject: [PATCH 3.16 013/305] ARM: fix put_user() for gcc-8

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@...db.de>

Building kernels before linux-4.7 with gcc-8 results in many build failures
when gcc triggers a check that was meant to catch broken compilers:

/tmp/ccCGMQmS.s:648: Error: .err encountered

According to the discussion in the gcc bugzilla, a local "register
asm()" variable is still supposed to be the correct way to force an
inline assembly to use a particular register, but marking it 'const'
lets the compiler do optimizations that break that, i.e the compiler is
free to treat the variable as either 'const' or 'register' in that case.

Upstream commit 9f73bd8bb445 ("ARM: uaccess: remove put_user() code
duplication") fixed this problem in linux-4.8 as part of a larger change,
but seems a little too big to be backported to 4.4.

Let's take the simplest fix and change only the one broken line in the
same way as newer kernels.

Suggested-by: Bernd Edlinger <bernd.edlinger@...mail.de>
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85745
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86673
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Johannes Pointner <h4nn35.work@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm/include/asm/uaccess.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -172,7 +172,7 @@ extern int __put_user_8(void *, unsigned
 	({								\
 		unsigned long __limit = current_thread_info()->addr_limit - 1; \
 		const typeof(*(p)) __user *__tmp_p = (p);		\
-		register const typeof(*(p)) __r2 asm("r2") = (x);	\
+		register typeof(*(p)) __r2 asm("r2") = (x);	\
 		register const typeof(*(p)) __user *__p asm("r0") = __tmp_p; \
 		register unsigned long __l asm("r1") = __limit;		\
 		register int __e asm("r0");				\