[dpdk-dev] [PATCH] mk: disable flag for no packet member warning

[dpdk-dev] [PATCH] mk: disable flag for no packet member warning

[kkanas]

From: Krzysztof Kanas <kkanas@marvell.com>

gcc prior 9 don't will add additional warning for unrecognized command
line option, but only when there is some other warning in the code, e.g
unused variable.

Fixes: a385972c3675 ("mk: disable warning for packed member pointer")
Cc: reshma.pattan@intel.com

Signed-off-by: Krzysztof Kanas <kkanas@marvell.com>
---
 mk/toolchain/gcc/rte.vars.mk | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mk/toolchain/gcc/rte.vars.mk b/mk/toolchain/gcc/rte.vars.mk
index b852fcfd7e24..1bd384f7ca3f 100644
--- a/mk/toolchain/gcc/rte.vars.mk
+++ b/mk/toolchain/gcc/rte.vars.mk
@@ -88,7 +88,9 @@ WERROR_FLAGS += -Wno-format-truncation
 endif
 
 # disable packed member unalign warnings
+ifeq ($(shell test $(HOST_GCC_VERSION) -gt 90 && echo 1), 1)
 WERROR_FLAGS += -Wno-address-of-packed-member
+endif
 
 export CC AS AR LD OBJCOPY OBJDUMP STRIP READELF
 export TOOLCHAIN_CFLAGS TOOLCHAIN_LDFLAGS TOOLCHAIN_ASFLAGS
-- 
2.21.0

Re: [dpdk-dev] [PATCH] mk: disable flag for no packet member warning

[Bruce Richardson]

On Mon, Jul 22, 2019 at 02:39:59PM +0200, kkanas@marvell.com wrote:
> From: Krzysztof Kanas <kkanas@marvell.com>
> 
> gcc prior 9 don't will add additional warning for unrecognized command
> line option, but only when there is some other warning in the code, e.g
> unused variable.
> 
I don't think this behaviour has changed in gcc 9. I just did a test
compile with gcc 9.1, and no warning was printed for flag
"-Wno-random-warnings". The online docs also make no mention of this
behaviour being conditional on GCC version [1].

/Bruce

[1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

Re: [dpdk-dev] [EXT] Re: [PATCH] mk: disable flag for no packet member warning

[Krzysztof Kanas]

On 19-07-22 14:44, Bruce Richardson wrote:
> External Email
> 
> ----------------------------------------------------------------------
> On Mon, Jul 22, 2019 at 02:39:59PM +0200, kkanas@marvell.com wrote:
> > From: Krzysztof Kanas <kkanas@marvell.com>
> > 
> > gcc prior 9 don't will add additional warning for unrecognized command
> > line option, but only when there is some other warning in the code, e.g
> > unused variable.
> > 
> I don't think this behaviour has changed in gcc 9. I just did a test
> compile with gcc 9.1, and no warning was printed for flag
> "-Wno-random-warnings". The online docs also make no mention of this
> behaviour being conditional on GCC version [1].
GCC changelog show that from 9.0 -Waddress-of-packed-member was added 
[1].

Test shows me that GCC prior to 9.0 won't complain about this flag, but 
in case of other warnings in file GCC will complain, e.g.,

cat > a.c
int main(int argc, char **argv)
{
	int a;
	return 0;
}

# gcc -Wall -Wno-address-of-packed-member a.c

a.c: In function ‘main’:
a.c:3:6: warning: unused variable ‘a’ [-Wunused-variable]
  int a;
      ^
a.c: At top level:
cc1: warning: unrecognized command line option ‘-Wno-address-of-packed-member’

But when line `int a;' is removed then no warning is issued.

Also I detected this, due to difference with meson build. Meson checks 
if compiler supports this flag and will not issue 
-Wno-address-of-packed-member to compiler.

> 
> /Bruce
> 
> [1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

[1] https://gcc.gnu.org/gcc-9/changes.html


-- 
-
Regards,
Krzysztof(Chris) Kanas

Re: [dpdk-dev] [EXT] Re: [PATCH] mk: disable flag for no packet member warning

[Bruce Richardson]

On Tue, Jul 23, 2019 at 09:05:50AM +0000, Krzysztof Kanas wrote:
> On 19-07-22 14:44, Bruce Richardson wrote:
> > External Email
> > 
> > ----------------------------------------------------------------------
> > On Mon, Jul 22, 2019 at 02:39:59PM +0200, kkanas@marvell.com wrote:
> > > From: Krzysztof Kanas <kkanas@marvell.com>
> > > 
> > > gcc prior 9 don't will add additional warning for unrecognized command
> > > line option, but only when there is some other warning in the code, e.g
> > > unused variable.
> > > 
> > I don't think this behaviour has changed in gcc 9. I just did a test
> > compile with gcc 9.1, and no warning was printed for flag
> > "-Wno-random-warnings". The online docs also make no mention of this
> > behaviour being conditional on GCC version [1].
> GCC changelog show that from 9.0 -Waddress-of-packed-member was added 
> [1].
> 
> Test shows me that GCC prior to 9.0 won't complain about this flag, but 
> in case of other warnings in file GCC will complain, e.g.,
> 
> cat > a.c
> int main(int argc, char **argv)
> {
> 	int a;
> 	return 0;
> }
> 
> # gcc -Wall -Wno-address-of-packed-member a.c
> 
> a.c: In function ‘main’:
> a.c:3:6: warning: unused variable ‘a’ [-Wunused-variable]
>   int a;
>       ^
> a.c: At top level:
> cc1: warning: unrecognized command line option ‘-Wno-address-of-packed-member’
> 
> But when line `int a;' is removed then no warning is issued.
> 
> Also I detected this, due to difference with meson build. Meson checks 
> if compiler supports this flag and will not issue 
> -Wno-address-of-packed-member to compiler.
> 
Yes, all that is correct, but there is no behaviour change in GCC 9. This
does not require a fix IMHO.

/Bruce