On Thu, May 26, 2016 at 12:55:45PM +0100, Maciej W. Rozycki wrote:
> 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!
>
May I suggest adding:
Fixes: ebb5e78cc634 ("MIPS: Initial implementation of a VDSO")
Patch looks good to me,
Reviewed-by: James Hogan <james.hogan@xxxxxxxxxx>
Cheers
James
> Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v4.3+
> ---
> linux-vdso-strict-aliasing.diff
> Index: linux-sfr-test/arch/mips/vdso/Makefile
> ===================================================================
> --- linux-sfr-test.orig/arch/mips/vdso/Makefile 2016-01-29 14:11:03.000000000 +0000
> +++ linux-sfr-test/arch/mips/vdso/Makefile 2016-05-26 12:37:55.327782000 +0100
> @@ -8,7 +8,8 @@ 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 \
> + -DDISABLE_BRANCH_PROFILING \
> $(call cc-option, -fno-stack-protector)
> aflags-vdso := $(ccflags-vdso) \
> $(filter -I%,$(KBUILD_CFLAGS)) \
>
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