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

[Bruce Richardson <bruce.richardson@intel.com>]

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
-- 
2.9.3