[PATCH 4.4 23/99] MIPS: VDSO: Build with `-fno-strict-aliasing

From: Greg Kroah-Hartman
Date: Sun Jun 05 2016 - 18:59:51 EST

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


From: Maciej W. Rozycki <macro@xxxxxxxxxx>

commit 94cc36b84acc29f543b48bc5ed786011b112a666 upstream.

Avoid an aliasing issue causing a build error in VDSO:

In file included from include/linux/srcu.h:34:0,
from include/linux/notifier.h:15,
from ./arch/mips/include/asm/uprobes.h:9,
from include/linux/uprobes.h:61,
from include/linux/mm_types.h:13,
from ./arch/mips/include/asm/vdso.h:14,
from arch/mips/vdso/vdso.h:27,
from arch/mips/vdso/gettimeofday.c:11:
include/linux/workqueue.h: In function 'work_static':
include/linux/workqueue.h:186:2: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
return *work_data_bits(work) & WORK_STRUCT_STATIC;
cc1: all warnings being treated as errors
make[2]: *** [arch/mips/vdso/gettimeofday.o] Error 1

with a CONFIG_DEBUG_OBJECTS_WORK configuration and GCC 5.2.0. Include
`-fno-strict-aliasing' along with compiler options used, as required for
kernel code, fixing a problem present since the introduction of VDSO
with commit ebb5e78cc634 ("MIPS: Initial implementation of a VDSO").

Thanks to Tejun for diagnosing this properly!

Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxx>
Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>
Fixes: ebb5e78cc634 ("MIPS: Initial implementation of a VDSO")
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: linux-mips@xxxxxxxxxxxxxx
Patchwork: https://patchwork.linux-mips.org/patch/13357/
Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/mips/vdso/Makefile | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -9,7 +9,8 @@ ccflags-vdso := \
$(filter -march=%,$(KBUILD_CFLAGS))
cflags-vdso := $(ccflags-vdso) \
$(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \
- -O2 -g -fPIC -fno-common -fno-builtin -G 0 -DDISABLE_BRANCH_PROFILING \
+ -O2 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
$(call cc-option, -fno-stack-protector)
aflags-vdso := $(ccflags-vdso) \
$(filter -I%,$(KBUILD_CFLAGS)) \