linux-kernel - [PATCH 3/8] bpftool: Conditionally add -Wformat-signedness flag

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Message-Id: <20250925-perf_build_android_ndk-v1-3-8b35aadde3dc@arm.com>
Date: Thu, 25 Sep 2025 11:26:27 +0100
From: Leo Yan <leo.yan@....com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>, 
 Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...nel.org>, 
 Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
 Quentin Monnet <qmo@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
 Nathan Chancellor <nathan@...nel.org>, 
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
 James Clark <james.clark@...aro.org>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org, 
 llvm@...ts.linux.dev, bpf@...r.kernel.org, Leo Yan <leo.yan@....com>
Subject: [PATCH 3/8] bpftool: Conditionally add -Wformat-signedness flag

clang-18.1.3 on Ubuntu 24.04.2 reports warning:

  warning: unknown warning option '-Wformat-signedness' [-Wunknown-warning-option]

Conditionally add the option only when it is supported by compiler.

Signed-off-by: Leo Yan <leo.yan@....com>
---
 tools/bpf/bpftool/Makefile | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index 9e9a5f006cd2aabe1e89bd83e394455c0d4473e0..948a0cc98b39d3f9afa0de73643eab04e8798ff5 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -64,11 +64,21 @@ $(LIBBPF_BOOTSTRAP)-clean: FORCE | $(LIBBPF_BOOTSTRAP_OUTPUT)
 prefix ?= /usr/local
 bash_compdir ?= /usr/share/bash-completion/completions
 
+try-run = $(shell set -e;		\
+	if ($(1)) >/dev/null 2>&1;	\
+	then echo "$(2)";		\
+	else echo "$(3)";		\
+	fi)
+
+__cc-option = $(call try-run,\
+	$(1) -Werror $(2) -c -x c /dev/null -o /dev/null,$(2),)
+cc-option = $(call __cc-option, $(CC),$(1))
+
 CFLAGS += -O2
 CFLAGS += -W
 CFLAGS += -Wall
 CFLAGS += -Wextra
-CFLAGS += -Wformat-signedness
+CFLAGS += $(call cc-option,-Wformat-signedness)
 CFLAGS += -Wno-unused-parameter
 CFLAGS += -Wno-missing-field-initializers
 CFLAGS += $(filter-out -Wswitch-enum -Wnested-externs,$(EXTRA_WARNINGS))

-- 
2.34.1