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

[Gavin Hu <Gavin.Hu@arm.com>]

Hi Bruce,

Thanks for your helpful comment, see my inline comments.

Best Regards,
Gavin

-----Original Message-----
From: Bruce Richardson <bruce.richardson@intel.com>
Sent: Monday, May 28, 2018 9:24 PM
To: Gavin Hu <Gavin.Hu@arm.com>
Cc: dev@dpdk.org; stable@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2 1/2] mk: fix cross build errors

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.

 [Gavin Hu] I tried your proposal, added "-Wno-implicit-fallthrough" before $( WERROR_FLAGS) in the pmdinfo Makefile.
It took precedence and made following " Wimplicit-fallthrough=2" useless, the compilation succeeded.

Is this what you mean?
Note the two options must be in this order, otherwise the compiling error still hit.

Another option is totally disable WERROR_FLAGS for pmdinfo, but this is not a best way as it includes a lot of other options.

toolchain/gcc/rte.vars.mk:46:WERROR_FLAGS := -W -Wall -Wstrict-prototypes -Wmissing-prototypes
toolchain/gcc/rte.vars.mk:47:WERROR_FLAGS += -Wmissing-declarations -Wold-style-definition -Wpointer-arith
toolchain/gcc/rte.vars.mk:48:WERROR_FLAGS += -Wcast-align -Wnested-externs -Wcast-qual
toolchain/gcc/rte.vars.mk:49:WERROR_FLAGS += -Wformat-nonliteral -Wformat-security
toolchain/gcc/rte.vars.mk:50:WERROR_FLAGS += -Wundef -Wwrite-strings -Wdeprecated
toolchain/gcc/rte.vars.mk:53:WERROR_FLAGS += -Werror
toolchain/gcc/rte.vars.mk:59:WERROR_FLAGS += -Wno-error=cast-align
toolchain/gcc/rte.vars.mk:67:WERROR_FLAGS += -Wno-missing-field-initializers
toolchain/gcc/rte.vars.mk:71:WERROR_FLAGS += -Wno-uninitialized
toolchain/gcc/rte.vars.mk:85:WERROR_FLAGS += -Wimplicit-fallthrough=2
toolchain/gcc/rte.vars.mk:87:WERROR_FLAGS += -Wno-format-truncation

/Bruce
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