linux-kernel - [PATCH 3.16.y-ckt 003/180] arm64: vdso: fix build error when switching from LE to BE

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Message-Id: <1430991989-23170-4-git-send-email-luis.henriques@canonical.com>
Date:	Thu,  7 May 2015 10:43:32 +0100
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Arun Chandran <achandran@...sta.com>,
	Will Deacon <will.deacon@....com>,
	Guenter Roeck <linux@...ck-us.net>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 003/180] arm64: vdso: fix build error when switching from LE to BE

3.16.7-ckt11 -stable review patch.  If anyone has any objections, please let me know.

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

From: Arun Chandran <achandran@...sta.com>

commit 1915e2ad1cf548217c963121e4076b3d44dd0169 upstream.

Building a kernel with CPU_BIG_ENDIAN fails if there are stale objects
from a !CPU_BIG_ENDIAN build. Due to a missing FORCE prerequisite on an
if_changed rule in the VDSO Makefile, we attempt to link a stale LE
object into the new BE kernel.

According to Documentation/kbuild/makefiles.txt, FORCE is required for
if_changed rules and forgetting it is a common mistake, so fix it by
'Forcing' the build of vdso. This patch fixes build errors like these:

arch/arm64/kernel/vdso/note.o: compiled for a little endian system and target is big endian
failed to merge target specific data of file arch/arm64/kernel/vdso/note.o

arch/arm64/kernel/vdso/sigreturn.o: compiled for a little endian system and target is big endian
failed to merge target specific data of file arch/arm64/kernel/vdso/sigreturn.o

Tested-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Arun Chandran <achandran@...sta.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Cc: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 arch/arm64/kernel/vdso/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 6d20b7d162d8..a268a9af0c2d 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -43,7 +43,7 @@ $(obj)/vdso-offsets.h: $(obj)/vdso.so.dbg FORCE
 	$(call if_changed,vdsosym)
 
 # Assembly rules for the .S files
-$(obj-vdso): %.o: %.S
+$(obj-vdso): %.o: %.S FORCE
 	$(call if_changed_dep,vdsoas)
 
 # Actual build commands
--
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