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

From: Vasily Gorbik <gor@linux.ibm.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.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: [PATCH 1/1] perf build: Allow nested externs to enable BUILD_BUG() usage
Date: Fri, 9 Oct 2020 08:47:45 +0200	[thread overview]
Message-ID: <patch-1.thread-d92c35.git-d92c35ca4748.your-ad-here.call-01602224864-ext-8734@work.hours> (raw)
In-Reply-To: <cover.thread-d92c35.your-ad-here.call-01602224864-ext-8734@work.hours>

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))
 
 include $(srctree)/tools/scripts/Makefile.arch
 
-- 
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