linux-kernel - [tip: objtool/core] perf build: Allow nested externs to enable BUILD

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Date:   Tue, 13 Oct 2020 10:12:46 -0000
From:   "tip-bot2 for Vasily Gorbik" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Ingo Molnar <mingo@...nel.org>, x86 <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [tip: objtool/core] perf build: Allow nested externs to enable
 BUILD_BUG() usage

The following commit has been merged into the objtool/core branch of tip:

Commit-ID:     ab0a40ea88204e1291b56da8128e2845fec8ee88
Gitweb:        https://git.kernel.org/tip/ab0a40ea88204e1291b56da8128e2845fec8ee88
Author:        Vasily Gorbik <gor@...ux.ibm.com>
AuthorDate:    Fri, 09 Oct 2020 14:25:23 +02:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Tue, 13 Oct 2020 12:08:32 +02:00

perf build: Allow nested externs to enable BUILD_BUG() usage

Currently the BUILD_BUG() macro is expanded to 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 would obviously 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>
Tested-by: Stephen Rothwell <sfr@...b.auug.org.au> # build tested
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Link: https://lore.kernel.org/r/patch-1.thread-251403.git-2514037e9477.your-ad-here.call-01602244460-ext-7088@work.hours
---
 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 190be4f..8137a60 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