Re: [PATCH] arm64/cache: silence -Woverride-init warnings

[Mark Rutland]

On Wed, Aug 07, 2019 at 11:29:16PM -0400, Qian Cai wrote:
> The commit 155433cb365e ("arm64: cache: Remove support for ASID-tagged
> VIVT I-caches") introduced some compiation warnings from GCC (and
> Clang) with -Winitializer-overrides),
> 
> arch/arm64/kernel/cpuinfo.c:38:26: warning: initialized field
> overwritten [-Woverride-init]
> [ICACHE_POLICY_VIPT]  = "VIPT",
>                         ^~~~~~
> arch/arm64/kernel/cpuinfo.c:38:26: note: (near initialization for
> 'icache_policy_str[2]')
> arch/arm64/kernel/cpuinfo.c:39:26: warning: initialized field
> overwritten [-Woverride-init]
> [ICACHE_POLICY_PIPT]  = "PIPT",
>                         ^~~~~~
> arch/arm64/kernel/cpuinfo.c:39:26: note: (near initialization for
> 'icache_policy_str[3]')
> arch/arm64/kernel/cpuinfo.c:40:27: warning: initialized field
> overwritten [-Woverride-init]
> [ICACHE_POLICY_VPIPT]  = "VPIPT",
>                          ^~~~~~~
> arch/arm64/kernel/cpuinfo.c:40:27: note: (near initialization for
> 'icache_policy_str[0]')
> 
> because it initializes icache_policy_str[0 ... 3] twice. Since
> arm64 developers are keen to keep the style of initializing a static
> array with a non-zero pattern first, just disable those warnings for
> both GCC and Clang of this file.
> 
> Fixes: 155433cb365e ("arm64: cache: Remove support for ASID-tagged VIVT I-caches")
> Signed-off-by: Qian Cai <cai@xxxxxx>

This is _not_ a fix, and should not require backporting to stable trees.

What about all the other instances that we have in mainline?

I really don't think that we need to go down this road; we're just going
to end up adding this to every file that happens to include a header
using this scheme...

Please just turn this off by default for clang.

If we want to enable this, we need a mechanism to permit overridable
assignments as we use range initializers for.

Thanks,
Mark.

> ---
>  arch/arm64/kernel/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
> index 478491f07b4f..397ed5f7be1e 100644
> --- a/arch/arm64/kernel/Makefile
> +++ b/arch/arm64/kernel/Makefile
> @@ -11,6 +11,9 @@ CFLAGS_REMOVE_ftrace.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_insn.o = $(CC_FLAGS_FTRACE)
>  CFLAGS_REMOVE_return_address.o = $(CC_FLAGS_FTRACE)
>  
> +CFLAGS_cpuinfo.o += $(call cc-disable-warning, override-init)
> +CFLAGS_cpuinfo.o += $(call cc-disable-warning, initializer-overrides)
> +
>  # Object file lists.
>  obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
>  			   entry-fpsimd.o process.o ptrace.o setup.o signal.o	\
> -- 
> 2.20.1 (Apple Git-117)
>