linux-kernel - Re: [PATCH RESEND 1/1] perf build: Allow nested externs to enable BUILD

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Date:   Mon, 12 Oct 2020 09:06:17 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Vasily Gorbik <gor@...ux.ibm.com>
Cc:     Jiri Olsa <jolsa@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: [PATCH RESEND 1/1] perf build: Allow nested externs to enable
 BUILD_BUG() usage

On Fri, Oct 9, 2020 at 8:35 PM Vasily Gorbik <gor@...ux.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@...b.auug.org.au>
> Signed-off-by: Vasily Gorbik <gor@...ux.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