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Message-ID: <4f947691-bf25-460b-bc08-da29de3fdaa6@kernel.org>
Date: Sun, 5 May 2024 23:36:14 +0100
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Subject: Re: [PATCH] bpftool, selftests/hid/bpf: fix 29 clang warnings
To: John Hubbard <jhubbard@nvidia.com>, Shuah Khan <shuah@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>, Benjamin Tissoires <bentiss@kernel.org>,
 Justin Stitt <justinstitt@google.com>,
 Peter Hutterer <peter.hutterer@who-t.net>,
 Jason Gerecke <jason.gerecke@wacom.com>,
 Joshua Dickens <joshua@joshua-dickens.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@google.com>, Hao Luo <haoluo@google.com>,
 Jiri Olsa <jolsa@kernel.org>, bpf@vger.kernel.org,
 linux-input@vger.kernel.org, Valentin Obst <kernel@valentinobst.de>,
 linux-kselftest@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
 llvm@lists.linux.dev
References: <20240505215636.63592-1-jhubbard@nvidia.com>
From: Quentin Monnet <qmo@kernel.org>
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In-Reply-To: <20240505215636.63592-1-jhubbard@nvidia.com>
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On 05/05/2024 22:56, John Hubbard wrote:
> When building either tools/bpf/bpftool, or tools/testing/selftests/hid,
> (the same Makefile is used for these), clang generates many instances of
> a warning that is useless here:
> 
>     "clang: warning: -lLLVM-17: 'linker' input unused"
> 
> Silence this in both locations, by disabling that warning when building
> with clang.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  tools/bpf/bpftool/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index e9154ace80ff..c7457921d136 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -133,6 +133,10 @@ CFLAGS += -DUSE_LIBCAP
>  LIBS += -lcap
>  endif
>  
> +ifneq ($(LLVM),)
> +    CFLAGS += -Wno-unused-command-line-argument
> +endif
Thanks! If possible, I'd rather keep the warning enabled, and fix the
command line instead. Looking at the error and the Makefile, we may not 
need the -lLLVM<version> in the CFLAGS at all, but only in $(LIBS). On
my setup, I can build successfully, without the warnings, with the
following patch:

------
diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
index b67454b45a49..dfa4f1bebbb3 100644
--- a/tools/bpf/bpftool/Makefile
+++ b/tools/bpf/bpftool/Makefile
@@ -147,7 +147,7 @@ ifeq ($(feature-llvm),1)
   # If LLVM is available, use it for JIT disassembly
   CFLAGS  += -DHAVE_LLVM_SUPPORT
   LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
-  CFLAGS  += $(shell $(LLVM_CONFIG) --cflags --libs $(LLVM_CONFIG_LIB_COMPONENTS))
+  CFLAGS  += $(shell $(LLVM_CONFIG) --cflags)
   LIBS    += $(shell $(LLVM_CONFIG) --libs $(LLVM_CONFIG_LIB_COMPONENTS))
   ifeq ($(shell $(LLVM_CONFIG) --shared-mode),static)
     LIBS += $(shell $(LLVM_CONFIG) --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
------

Could you please check whether that works on your side, too?

Quentin