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Date:   Fri, 9 Oct 2020 13:23:27 +0200
From:   Jiri Olsa <jolsa@redhat.com>
To:     Vasily Gorbik <gor@linux.ibm.com>
Cc:     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 1/1] perf build: Allow nested externs to enable
 BUILD_BUG() usage
Message-ID: <20201009112327.GC656950@krava>
References: <20201009152846.072e6bbf@canb.auug.org.au>
 <cover.thread-d92c35.your-ad-here.call-01602224864-ext-8734@work.hours>
 <patch-1.thread-d92c35.git-d92c35ca4748.your-ad-here.call-01602224864-ext-8734@work.hours>
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On Fri, Oct 09, 2020 at 08:47:45AM +0200, Vasily Gorbik wrote:
> Currently BUILD_BUG() macro is expanded to smth like the following:
>    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>
> ---
>  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 190be4fa5c21..8137a6046a47 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))

looks good, but I can't apply the patch with 'git am'

	Applying: perf build: Allow nested externs to enable BUILD_BUG() usage
	error: patch failed: tools/perf/Makefile.config:16
	error: tools/perf/Makefile.config: patch does not apply
	Patch failed at 0001 perf build: Allow nested externs to enable BUILD_BUG() usage
	hint: Use 'git am --show-current-patch=diff' to see the failed patch
	When you have resolved this problem, run "git am --continue".
	If you prefer to skip this patch, run "git am --skip" instead.
	To restore the original branch and stop patching, run "git am --abort".

I wonder it's that picture at the bottom ;-)

jirka


>  
>  include $(srctree)/tools/scripts/Makefile.arch
>  
> -- 
> ⣿⣿⣿⣿⢋⡀⣀⠹⣿⣿⣿⣿
> ⣿⣿⣿⣿⠠⣶⡦⠀⣿⣿⣿⣿
> ⣿⣿⣿⠏⣴⣮⣴⣧⠈⢿⣿⣿
> ⣿⣿⡏⢰⣿⠖⣠⣿⡆⠈⣿⣿
> ⣿⢛⣵⣄⠙⣶⣶⡟⣅⣠⠹⣿
> ⣿⣜⣛⠻⢎⣉⣉⣀⠿⣫⣵⣿