Re: [dpdk-stable] [dpdk-dev] [PATCH 1/2] mk: fix unsupported flag error on armhf architercture

["Phil Yang (Arm Technology China)" <Phil.Yang@arm.com>]

> -----Original Message-----
> From: Bruce Richardson <bruce.richardson@intel.com>
> Sent: Wednesday, November 27, 2019 5:30 PM
> To: Phil Yang (Arm Technology China) <Phil.Yang@arm.com>
> Cc: thomas@monjalon.net; dev@dpdk.org; david.marchand@redhat.com;
> jerinj@marvell.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm Technology China)
> <Gavin.Hu@arm.com>; Joyce Kong (Arm Technology China)
> <Joyce.Kong@arm.com>; nd <nd@arm.com>; stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 1/2] mk: fix unsupported flag error on armhf
> architercture
> 
> On Wed, Nov 27, 2019 at 08:09:22AM +0000, Phil Yang (Arm Technology China)
> wrote:
> > > -----Original Message-----
> > > From: Thomas Monjalon <thomas@monjalon.net>
> > > Sent: Wednesday, November 27, 2019 1:02 AM
> > > To: Phil Yang (Arm Technology China) <Phil.Yang@arm.com>
> > > Cc: dev@dpdk.org; Bruce Richardson <bruce.richardson@intel.com>;
> > > david.marchand@redhat.com; jerinj@marvell.com; Honnappa
> Nagarahalli
> > > <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm Technology China)
> > > <Gavin.Hu@arm.com>; Joyce Kong (Arm Technology China)
> > > <Joyce.Kong@arm.com>; nd <nd@arm.com>; stable@dpdk.org
> > > Subject: Re: [dpdk-dev] [PATCH 1/2] mk: fix unsupported flag error on
> armhf
> > > architercture
> > >
> > > 12/11/2019 07:40, Phil Yang (Arm Technology China):
> > > > > -----Original Message-----
> > > > > From: Thomas Monjalon <thomas@monjalon.net>
> > > > > Sent: Tuesday, November 12, 2019 2:03 PM
> > > > > To: Phil Yang (Arm Technology China) <Phil.Yang@arm.com>
> > > > > Cc: Bruce Richardson <bruce.richardson@intel.com>; dev@dpdk.org;
> > > > > david.marchand@redhat.com; jerinj@marvell.com; Honnappa
> > > Nagarahalli
> > > > > <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm Technology China)
> > > > > <Gavin.Hu@arm.com>; Joyce Kong (Arm Technology China)
> > > > > <Joyce.Kong@arm.com>; nd <nd@arm.com>; stable@dpdk.org
> > > > > Subject: Re: [dpdk-dev] [PATCH 1/2] mk: fix unsupported flag error
> on
> > > armhf
> > > > > architercture
> > > > >
> > > > > 12/11/2019 06:25, Phil Yang (Arm Technology China):
> > > > > > From: Bruce Richardson <bruce.richardson@intel.com>
> > > > > > > On Mon, Nov 11, 2019 at 06:34:20PM +0800, Phil Yang wrote:
> > > > > > > > The older version (e.g. version 7.4.0 ) of GNU C compiler for the
> > > armhf
> > > > > > > > architecture doesn't support the flag '-Wno-address-of-packed-
> > > > > member',
> > > > > > > > so remove this flag for aarch32.
> > > > > > > >
> > > > > > > > Fixes: a385972c3675 ("mk: disable warning for packed member
> > > pointer")
> > > > > > > > Cc: stable@dpdk.org
> > > > > > > >
> > > > > > > > Signed-off-by: Phil Yang <phil.yang@arm.com>
> > > > > > > > Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> > > > > > > > Tested-by: Joyce Kong <joyce.kong@arm.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 9fc7041..ec0cbbf 100644
> > > > > > > > --- a/mk/toolchain/gcc/rte.vars.mk
> > > > > > > > +++ b/mk/toolchain/gcc/rte.vars.mk
> > > > > > > > @@ -100,7 +100,9 @@ WERROR_FLAGS += -Wno-format-
> truncation
> > > > > > > >  endif
> > > > > > > >
> > > > > > > >  # disable packed member unalign warnings
> > > > > > > > +ifneq ($(CONFIG_RTE_ARCH_ARM), y)
> > > > > > > >  WERROR_FLAGS += -Wno-address-of-packed-member
> > > > > > > > +endif
> > > > > > > >
> > > > > > > You don't need to do this, as gcc will not complain about this
> unknown
> > > > > flag
> > > > > > > unless you have other issues in your code.[1] I think it's better to
> > > keep
> > > > > the
> > > > > > > code clean in this case, otherwise we'll have the code littered with
> > > > > > > conditionals for various flags.
> > > > > > >
> > > > > > > /Bruce
> > > > > > >
> > > > > > > [1] https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html
> > > > > > > "When an unrecognized warning option is requested (e.g.,
> > > > > > > -Wunknown-warning), GCC emits a diagnostic stating that the
> option
> > > is
> > > > > not
> > > > > > > recognized. However, if the -Wno- form is used, the behavior is
> > > slightly
> > > > > > > different: no diagnostic is produced for -Wno-unknown-warning
> > > unless
> > > > > other
> > > > > > > diagnostics are being produced. This allows the use of new -Wno-
> > > options
> > > > > > > with old compilers, but if something goes wrong, the compiler
> warns
> > > that
> > > > > an
> > > > > > > unrecognized option is present."
> > > > > >
> > > > > > Thanks, Bruce.
> > > > > >
> > > > > > There are thousands of warnings with alignment when compiling for
> > > > > ARMv7 (ARMv7 supports unaligned memory access).
> > > > > > Without this new flag, the build system works fine for ARMv7.  So I
> add
> > > this
> > > > > conditional for ARMv7 only.
> > > > > > I agree with you we should clean up the code, but it needs a lot of
> > > effort to
> > > > > achieve that.
> > > > > > This patch is going to make the ARMv7 target build successfully
> during
> > > this
> > > > > period.
> > > > >
> > > > > I would go the opposite direction.
> > > > > I think we should remove all warnings disablement like "-Wno-
> > > something",
> > > > > and clean the code.
> > > >
> > > > Thanks, Thomas.
> > > >
> > > > I think it is a compiler issue rather than a code defect in this case, as It
> > > cannot recognize the '-Waddress-of-packed-member' flag.
> > > > "arm-linux-gnueabihf-gcc: error: unrecognized command line option '-
> > > Waddress-of-packed-member'"
> > > >
> > > > >
> > > > > If you want to allow building ARMv7, you can just allow warnings as
> not
> > > > > errors.
> > > > > So we will still see something is wrong but it won't prevent from
> building.
> > > >
> > > > Yes. We did this already, all the alignment issues are emitted as
> warnings
> > > on ARMv7.
> > > > Please see these two commits:
> > > > 79fa5c2a9992 ("mk: ignore alignment errors for ARMv7")
> > > > 6433c19105e8 ("mk: generalize strict alignment warning handling")
> > >
> > > I don't know what to do with this patch.
> > > I think it is not how it should work,
> > > but you say your compiler has a real bug.
> > Agree with you, however I haven't found a better solution for this issue yet.
> >
> > >
> > > Can you confirm which compiler is it?
> >
> > Please check the packet information dumped below, it is the latest version
> in Ubuntu 18.04 LTS.
> > $ sudo apt show gcc-arm-linux-gnueabihf
> > Package: gcc-arm-linux-gnueabihf
> > Version: 4:7.4.0-1ubuntu2.3
> > Priority: optional
> > Section: devel
> > Source: gcc-defaults (1.176ubuntu2.3)
> > Origin: Ubuntu
> >
> > > Does it prevent to compile even with -Wno-error ?
> > Yes, it does. I put one piece of the compiling log bellow. Please take a look.
> >
> > $ make -j1 CROSS=arm-linux-gnueabihf- T=arm-armv7a-linuxapp-gcc
> RTE_DEVEL_BUILD=y
> 
> RTE_DEVEL_BUILD turns on -Werror, while what Thomas is asking about is
> using the opposite flag "-Wno-error". Can you do a non-developer build or
> put "-Wno-error" in EXTRA_CFLAGS to test this.

Thanks, Bruce. 
There is no compiling issue for the non-developer build and "-Wno-error" flag build.