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Date: Wed, 20 Jan 2021 22:36:27 -0700
From: Nathan Chancellor <natechancellor@...il.com>
To: Tiezhu Yang <yangtiezhu@...ngson.cn>
Cc: Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
netdev@...r.kernel.org, bpf@...r.kernel.org,
clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
Xuefeng Li <lixuefeng@...ngson.cn>,
Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH bpf-next v3] samples/bpf: Update build procedure for
manually compiling LLVM and Clang
On Thu, Jan 21, 2021 at 01:27:35PM +0800, Tiezhu Yang wrote:
> The current LLVM and Clang build procedure in samples/bpf/README.rst is
> out of date. See below that the links are not accessible any more.
>
> $ git clone http://llvm.org/git/llvm.git
> Cloning into 'llvm'...
> fatal: unable to access 'http://llvm.org/git/llvm.git/': Maximum (20) redirects followed
> $ git clone --depth 1 http://llvm.org/git/clang.git
> Cloning into 'clang'...
> fatal: unable to access 'http://llvm.org/git/clang.git/': Maximum (20) redirects followed
>
> The LLVM community has adopted new ways to build the compiler. There are
> different ways to build LLVM and Clang, the Clang Getting Started page [1]
> has one way. As Yonghong said, it is better to copy the build procedure
> in Documentation/bpf/bpf_devel_QA.rst to keep consistent.
>
> I verified the procedure and it is proved to be feasible, so we should
> update README.rst to reflect the reality. At the same time, update the
> related comment in Makefile.
>
> Additionally, as Fangrui said, the dir llvm-project/llvm/build/install is
> not used, BUILD_SHARED_LIBS=OFF is the default option [2], so also change
> Documentation/bpf/bpf_devel_QA.rst together.
>
> [1] https://clang.llvm.org/get_started.html
> [2] https://www.llvm.org/docs/CMake.html
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> Acked-by: Yonghong Song <yhs@...com>
Reviewed-by: Nathan Chancellor <natechancellor@...il.com>
Small comment below.
> ---
>
> v2: Update the commit message suggested by Yonghong,
> thank you very much.
>
> v3: Remove the default option BUILD_SHARED_LIBS=OFF
> and just mkdir llvm-project/llvm/build suggested
> by Fangrui.
>
> Documentation/bpf/bpf_devel_QA.rst | 3 +--
> samples/bpf/Makefile | 2 +-
> samples/bpf/README.rst | 16 +++++++++-------
> 3 files changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/bpf/bpf_devel_QA.rst b/Documentation/bpf/bpf_devel_QA.rst
> index 5b613d2..18788bb 100644
> --- a/Documentation/bpf/bpf_devel_QA.rst
> +++ b/Documentation/bpf/bpf_devel_QA.rst
> @@ -506,11 +506,10 @@ that set up, proceed with building the latest LLVM and clang version
> from the git repositories::
>
> $ git clone https://github.com/llvm/llvm-project.git
> - $ mkdir -p llvm-project/llvm/build/install
> + $ mkdir -p llvm-project/llvm/build
> $ cd llvm-project/llvm/build
> $ cmake .. -G "Ninja" -DLLVM_TARGETS_TO_BUILD="BPF;X86" \
> -DLLVM_ENABLE_PROJECTS="clang" \
> - -DBUILD_SHARED_LIBS=OFF \
> -DCMAKE_BUILD_TYPE=Release \
> -DLLVM_BUILD_RUNTIME=OFF
> $ ninja
> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> index 26fc96c..d061446 100644
> --- a/samples/bpf/Makefile
> +++ b/samples/bpf/Makefile
> @@ -208,7 +208,7 @@ TPROGLDLIBS_xdpsock += -pthread -lcap
> TPROGLDLIBS_xsk_fwd += -pthread
>
> # Allows pointing LLC/CLANG to a LLVM backend with bpf support, redefine on cmdline:
> -# make M=samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> +# make M=samples/bpf LLC=~/git/llvm-project/llvm/build/bin/llc CLANG=~/git/llvm-project/llvm/build/bin/clang
> LLC ?= llc
> CLANG ?= clang
> OPT ?= opt
> diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
> index dd34b2d..23006cb 100644
> --- a/samples/bpf/README.rst
> +++ b/samples/bpf/README.rst
> @@ -65,17 +65,19 @@ To generate a smaller llc binary one can use::
> Quick sniplet for manually compiling LLVM and clang
> (build dependencies are cmake and gcc-c++)::
Technically, ninja is now a build dependency as well, it might be worth
mentioning that here (usually the package is ninja or ninja-build).
Regardless of whether that is addressed or not (because it is small),
feel free to carry forward my tag in any future revisions unless they
drastically change.
> - $ git clone http://llvm.org/git/llvm.git
> - $ cd llvm/tools
> - $ git clone --depth 1 http://llvm.org/git/clang.git
> - $ cd ..; mkdir build; cd build
> - $ cmake .. -DLLVM_TARGETS_TO_BUILD="BPF;X86"
> - $ make -j $(getconf _NPROCESSORS_ONLN)
> + $ git clone https://github.com/llvm/llvm-project.git
> + $ mkdir -p llvm-project/llvm/build
> + $ cd llvm-project/llvm/build
> + $ cmake .. -G "Ninja" -DLLVM_TARGETS_TO_BUILD="BPF;X86" \
> + -DLLVM_ENABLE_PROJECTS="clang" \
> + -DCMAKE_BUILD_TYPE=Release \
> + -DLLVM_BUILD_RUNTIME=OFF
> + $ ninja
>
> It is also possible to point make to the newly compiled 'llc' or
> 'clang' command via redefining LLC or CLANG on the make command line::
>
> - make M=samples/bpf LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
> + make M=samples/bpf LLC=~/git/llvm-project/llvm/build/bin/llc CLANG=~/git/llvm-project/llvm/build/bin/clang
>
> Cross compiling samples
> -----------------------
> --
> 2.1.0
>
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