Re: [PATCH bpf-next v3] samples/bpf: Update build procedure for manually compiling LLVM and Clang

[Nathan Chancellor <natechancellor@gmail.com>]

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 out of date.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@loongson.cn>
> Acked-by: Yonghong Song <yhs@fb.com>

Reviewed-by: Nathan Chancellor <natechancellor@gmail.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
>