Re: [PATCH RESEND 1/1] perf build: Allow nested externs to enable BUILD_BUG() usage

From: Sedat Dilek <sedat.dilek@gmail.com>
To: Vasily Gorbik <gor@linux.ibm.com>
Cc: Jiri Olsa <jolsa@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux Next Mailing List <linux-next@vger.kernel.org>
Subject: Re: [PATCH RESEND 1/1] perf build: Allow nested externs to enable BUILD_BUG() usage
Date: Mon, 12 Oct 2020 09:06:17 +0200	[thread overview]
Message-ID: <CA+icZUVk_OMN76PCug-QAAzMOw=EWFwt=-MdxDVGpj5NYQ-bvg@mail.gmail.com> (raw)
In-Reply-To: <patch-1.thread-251403.git-2514037e9477.your-ad-here.call-01602244460-ext-7088@work.hours>

On Fri, Oct 9, 2020 at 8:35 PM Vasily Gorbik <gor@linux.ibm.com> wrote:
>
> Currently BUILD_BUG() macro is expanded to smth like the following:

Two feedbacks:

#1: Greg KH told me to expand abbreviated words, here "smth = something".

#2: Interesting to see an ASCII-art in the signature is causing such troubles.

- Sedat -

>    do {
>            extern void __compiletime_assert_0(void)
>                    __attribute__((error("BUILD_BUG failed")));
>            if (!(!(1)))
>                    __compiletime_assert_0();
>    } while (0);
>
> If used in a function body this obviously would produce build errors
> with -Wnested-externs and -Werror.
>
> To enable BUILD_BUG() usage in tools/arch/x86/lib/insn.c which perf
> includes in intel-pt-decoder, build perf without -Wnested-externs.
>
> Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
> ---
>  Resend with no fancy signatures.
>
>  tools/perf/Makefile.config | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
> index 854da830b5ca..834061e94e7c 100644
> --- a/tools/perf/Makefile.config
> +++ b/tools/perf/Makefile.config
> @@ -16,7 +16,7 @@ $(shell printf "" > $(OUTPUT).config-detected)
>  detected     = $(shell echo "$(1)=y"       >> $(OUTPUT).config-detected)
>  detected_var = $(shell echo "$(1)=$($(1))" >> $(OUTPUT).config-detected)
>
> -CFLAGS := $(EXTRA_CFLAGS) $(EXTRA_WARNINGS)
> +CFLAGS := $(EXTRA_CFLAGS) $(filter-out -Wnested-externs,$(EXTRA_WARNINGS))
>
>  include $(srctree)/tools/scripts/Makefile.arch
>
> --
> 2.25.4