Re: [PATCH v2 1/2] mk: fix cross build errors

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

On Mon, May 28, 2018 at 02:53:47AM -0400, Gavin Hu wrote:
> The "-Wimplicit-fallthrough=2" option was introduced into gcc 7.0, it was
> enabled when the cross compiler gcc is greater than 7.0, but for the host
> side buildtools/pmdinfogen, if the native is older than 7.0, it should not
> be enabled.
> 
> The fix is to differentiate the host gcc Werror options from the cross gcc.
> 
> gcc -Wp,-MD,./.pmdinfogen.o.d.tmp  -W -Wall -Wstrict-prototypes
> -Wmissing-prototypes -Wmissing-declarations -Wold-style-definition
> -Wpointer-arith -Wcast-align -Wnested-externs -Wcast-qual
> -Wformat-nonliteral -Wformat-security -Wundef -Wwrite-strings -Wdeprecated
> -Werror -Wimplicit-fallthrough=2 -Dbbb -Wno-format-truncation -g
> -I/home/gavin/arm_repo/dpdk/build/include    -o pmdinfogen.o -c
> ~/dpdk/buildtools/pmdinfogen/pmdinfogen.c gcc: error:
> unrecognized command line option ‘-Wimplicit-fallthrough=2’
> ~/dpdk/mk/internal/rte.compile-pre.mk:114: recipe for target 'pmdinfogen.o'
> failed make[3]: *** [pmdinfogen.o] Error 1
> 
> Fixes: ced3e6f8 ("mk: adjust gcc flags for new gcc 7 warnings")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Reviewed-by: Steve Capper <Steve.Capper@arm.com>
> Reviewed-by: Thomas Monjalon <thomas@monjalon.net>
> ---

Would a simpler solution for this not be to put "-Wno-implicit-fallthrough"
for pmdinfogen? GCC will not give a warning for an unrecognised "-Wno"
flag when compiling, unless there are other errors. This means we can just
use the flag without bothering with version checks.

/Bruce