Re: [dpdk-dev] [PATCH 01/10] mk: adjust gcc flags for new gcc 7 warnings

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu,  4 May 2017 16:38:13 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> There are two new warnings in GCC 7 that cause problems in the DPDK
> compile.
> 
> 1. GCC now warns if you have a switch fall-through without a suitable
> comment indicating that it was intentional. The compiler supports a number
> of levels of warning which are triggered depending on the type of message
> used, with level 3 being the default. To accept a wider range of possible
> fall-through messages, we adjust this down to level 2.
> 
> 2. GCC also warns about an snprintf where there may be truncation and the
> return value is not checked. Given that we often use snprintf in DPDK in
> place of strncpy, and in many cases where truncation is not a problem, we
> can just disable this particular warning.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  mk/toolchain/gcc/rte.vars.mk | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/mk/toolchain/gcc/rte.vars.mk b/mk/toolchain/gcc/rte.vars.mk
> index 5caa600..3834e00 100644
> --- a/mk/toolchain/gcc/rte.vars.mk
> +++ b/mk/toolchain/gcc/rte.vars.mk
> @@ -99,5 +99,12 @@ ifeq ($(shell test $(GCC_VERSION) -lt 47 && echo 1), 1)
>  WERROR_FLAGS += -Wno-uninitialized
>  endif
>  
> +ifeq ($(shell test $(GCC_VERSION) -gt 70 && echo 1), 1)
> +# Tell GCC only to error for switch fallthroughs without a suitable comment
> +WERROR_FLAGS += -Wimplicit-fallthrough=2
> +# Ignore errors for snprintf truncation
> +WERROR_FLAGS += -Wno-format-truncation
> +endif
> +
>  export CC AS AR LD OBJCOPY OBJDUMP STRIP READELF
>  export TOOLCHAIN_CFLAGS TOOLCHAIN_LDFLAGS TOOLCHAIN_ASFLAGS

Please fix the code not neuter  warnings