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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@linux.ibm.com>
AuthorDate: Fri, 09 Oct 2020 14:25:23 +02:00
Committer: Ingo Molnar <mingo@kernel.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@canb.auug.org.au>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au> # build tested
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.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

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