Re: [PATCH v2] selftests/user_events: silence a clang warning: address of packed member

[John Hubbard]

On 5/28/24 1:35 PM, Nathan Chancellor wrote:
> On Tue, May 28, 2024 at 01:28:33PM -0700, Nathan Chancellor wrote:
..
> > > diff --git a/tools/testing/selftests/user_events/Makefile b/tools/testing/selftests/user_events/Makefile
> > > index 10fcd0066203..617e94344711 100644
> > > --- a/tools/testing/selftests/user_events/Makefile
> > > +++ b/tools/testing/selftests/user_events/Makefile
> > > @@ -1,5 +1,10 @@
> > >   # SPDX-License-Identifier: GPL-2.0
> > >   CFLAGS += -Wl,-no-as-needed -Wall $(KHDR_INCLUDES)
> > > +
> > > +ifneq ($(LLVM),)
> >
> > Perhaps it would be better if this were
> >
> >    ifeq ($(CC),clang)
> >
> > as that would catch both CC=clang and LLVM=1 users? I haven't tested
> > this though.

That exact fix wouldn't quite work for the LLVM=1 case, because there,
CC is set to a horrible long mess, like this:

    CC = clang --target=x86_64-pc-linux-gnu -fintegrated-as

..but I see what you mean. It's not covering the CC=clang case.

> Hmmm, now that I am actually looking at tools/testing/selftests/lib.mk,
> it seems like CC is only set to clang when $(LLVM) is set, so keeping it
> the way it is now is probably best. Sorry about that, I am not too
> familiar with the tools build system.

That's true, and the patch here was admittedly only attempting to fix
the LLVM=1 case. However, I recall someone is building these kselftests
via "make CC=clang", which caught me by surprise, so I suppose that
should be fixed too. Maybe all of these checks (there are a few other
patches, but none merged yet) should be effectively:

    "if LLVM==1 or CC==clang, then apply the clang fix(es)"
	

> > Additionally, I think it would be good to mention that
> > -Wno-address-of-packed-member is GCC's default, whereas Clang enables
> > -Waddress-of-packed-member by default.

OK, I'll add that to a short comment nearby.

> > > +    CFLAGS += -Wno-address-of-packed-member
> > > +endif
> > > +
> > >   LDLIBS += -lrt -lpthread -lm
> > >   
> > >   TEST_GEN_PROGS = ftrace_test dyn_test perf_test abi_test
> > >
> > > base-commit: 2bfcfd584ff5ccc8bb7acde19b42570414bf880b
> > > --
> > > 2.45.1

thanks,
--
John Hubbard
NVIDIA