From: Quentin Monnet <qmo@kernel.org>
To: Leo Yan <leo.yan@arm.com>, Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
Yonghong Song <yonghong.song@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@fomichev.me>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>, Shuah Khan <shuah@kernel.org>,
Lorenz Bauer <lmb@isovalent.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
Namhyung Kim <namhyung@kernel.org>,
Ian Rogers <irogers@google.com>,
James Clark <james.clark@linaro.org>, Kees Cook <kees@kernel.org>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, llvm@lists.linux.dev
Subject: Re: [PATCH bpf-next v2 1/8] bpftool: Pass host flags to bootstrap libbpf
Date: Wed, 3 Jun 2026 10:21:58 +0100 [thread overview]
Message-ID: <2b72da46-bf83-406f-bf5b-022f8e0ac04f@kernel.org> (raw)
In-Reply-To: <20260602-tools_build_fix_zero_init_bpf_only-v2-1-c76e5250ea1c@arm.com>
2026-06-02 15:47 UTC+0100 ~ Leo Yan <leo.yan@arm.com>
> bpftool builds a bootstrap libbpf with HOSTCC, but the libbpf submake can
> still inherit target build flags through CFLAGS. This can break cross
> builds when host objects are compiled with target-only options.
>
> Since HOST_CFLAGS contains warning options that are not suitable for
> building libbpf, use LIBBPF_BOOTSTRAP_CFLAGS with the warning options
> removed to build the bootstrap libbpf. Clear EXTRA_CFLAGS so target
> extra flags are not mixed into the host bootstrap libbpf build.
>
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
> tools/bpf/bpftool/Makefile | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 0febf60e1b64656035dfe93cd15cba090015587a..1f033e578f90a2d6b93168ab41399de758bdf659 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -47,7 +47,8 @@ $(LIBBPF_INTERNAL_HDRS): $(LIBBPF_HDRS_DIR)/%.h: $(BPF_DIR)/%.h | $(LIBBPF_HDRS_
> $(LIBBPF_BOOTSTRAP): $(wildcard $(BPF_DIR)/*.[ch] $(BPF_DIR)/Makefile) | $(LIBBPF_BOOTSTRAP_OUTPUT)
> $(Q)$(MAKE) -C $(BPF_DIR) OUTPUT=$(LIBBPF_BOOTSTRAP_OUTPUT) \
> DESTDIR=$(LIBBPF_BOOTSTRAP_DESTDIR:/=) prefix= \
> - ARCH= CROSS_COMPILE= CC="$(HOSTCC)" LD="$(HOSTLD)" AR="$(HOSTAR)" $@ install_headers
> + ARCH= CROSS_COMPILE= CC="$(HOSTCC)" LD="$(HOSTLD)" AR="$(HOSTAR)" \
> + CFLAGS="$(LIBBPF_BOOTSTRAP_CFLAGS)" EXTRA_CFLAGS= $@ install_headers
>
> $(LIBBPF_BOOTSTRAP_INTERNAL_HDRS): $(LIBBPF_BOOTSTRAP_HDRS_DIR)/%.h: $(BPF_DIR)/%.h | $(LIBBPF_BOOTSTRAP_HDRS_DIR)
> $(call QUIET_INSTALL, $@)
> @@ -92,6 +93,9 @@ HOST_CFLAGS := $(subst -I$(LIBBPF_INCLUDE),-I$(LIBBPF_BOOTSTRAP_INCLUDE),\
> $(subst $(CLANG_CROSS_FLAGS),,$(CFLAGS)))
> HOST_LDFLAGS := $(LDFLAGS)
>
> +# Remove warnings for libbpf bootstrap build
Nitpick: We could expand this comment to briefly explain why. Not sure
it's worth a respin, though.
> +LIBBPF_BOOTSTRAP_CFLAGS := $(filter-out -W -Wall -Wextra -Wformat -Wformat-signedness,$(HOST_CFLAGS))
Do we need to remove all warnings, or would it be sufficient to take out
-Wformat and -Wformat-signedness? I don't mind removing them all if
necessary, just asking.
Acked-by: Quentin Monnet <qmo@kernel.org>
Thanks!
next prev parent reply other threads:[~2026-06-03 9:22 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-02 14:47 [PATCH bpf-next v2 0/8] tools build: bpf: Append EXTRA_CFLAGS and HOST_EXTRACFLAGS Leo Yan
2026-06-02 14:47 ` [PATCH bpf-next v2 1/8] bpftool: Pass host flags to bootstrap libbpf Leo Yan
2026-06-03 9:21 ` Quentin Monnet [this message]
2026-06-02 14:47 ` [PATCH bpf-next v2 2/8] bpftool: Avoid adding EXTRA_CFLAGS to HOST_CFLAGS Leo Yan
2026-06-02 14:47 ` [PATCH bpf-next v2 3/8] bpftool: Append extra host flags Leo Yan
2026-06-02 14:47 ` [PATCH bpf-next v2 4/8] libbpf: Initialize CFLAGS before including Makefile.include Leo Yan
2026-06-02 15:11 ` sashiko-bot
2026-06-02 14:47 ` [PATCH bpf-next v2 5/8] tools/bpf: build: Append extra cflags Leo Yan
2026-06-13 1:09 ` Ihor Solodrai
2026-06-02 14:47 ` [PATCH bpf-next v2 6/8] selftests/bpf: Initialize operation name before use Leo Yan
2026-06-13 1:11 ` Ihor Solodrai
2026-06-02 14:47 ` [PATCH bpf-next v2 7/8] selftests/bpf: Use common CFLAGS for urandom_read Leo Yan
2026-06-02 15:32 ` bot+bpf-ci
2026-06-02 17:25 ` sashiko-bot
2026-06-13 1:37 ` Ihor Solodrai
2026-06-02 14:47 ` [PATCH bpf-next v2 8/8] selftests/bpf: Avoid static LLVM linking for cross builds Leo Yan
2026-06-02 17:33 ` sashiko-bot
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=2b72da46-bf83-406f-bf5b-022f8e0ac04f@kernel.org \
--to=qmo@kernel.org \
--cc=acme@kernel.org \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=eddyz87@gmail.com \
--cc=haoluo@google.com \
--cc=irogers@google.com \
--cc=james.clark@linaro.org \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=justinstitt@google.com \
--cc=kees@kernel.org \
--cc=kpsingh@kernel.org \
--cc=leo.yan@arm.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=llvm@lists.linux.dev \
--cc=lmb@isovalent.com \
--cc=martin.lau@linux.dev \
--cc=morbo@google.com \
--cc=namhyung@kernel.org \
--cc=nathan@kernel.org \
--cc=nick.desaulniers+lkml@gmail.com \
--cc=sdf@fomichev.me \
--cc=shuah@kernel.org \
--cc=song@kernel.org \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox