linux-kernel - Re: [PATCH bpf] samples/bpf: Update README.rst for manually compiling LLVM and clang

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Date:   Mon, 18 Jan 2021 10:01:53 -0800
From:   Yonghong Song <yhs@...com>
To:     Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <clang-built-linux@...glegroups.com>,
        <linux-kernel@...r.kernel.org>, Xuefeng Li <lixuefeng@...ngson.cn>
Subject: Re: [PATCH bpf] samples/bpf: Update README.rst for manually compiling
 LLVM and clang



On 1/18/21 12:53 AM, Tiezhu Yang wrote:
> In the current samples/bpf/README.rst, the url of llvm and clang git
> may be out of date, they are unable to access:
> 
> $ 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 Clang Getting Started page [1] might have more accurate information,
> I verified the procedure and it is proved to be feasible, so we should
> update it to reflect the reality.
> 
> [1] https://clang.llvm.org/get_started.html
> 
> Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
> ---
>   samples/bpf/README.rst | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
> index dd34b2d..f606c08 100644
> --- a/samples/bpf/README.rst
> +++ b/samples/bpf/README.rst
> @@ -65,11 +65,9 @@ To generate a smaller llc binary one can use::
>   Quick sniplet for manually compiling LLVM and clang
>   (build dependencies are cmake and gcc-c++)::
>   
> - $ 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"
> + $ git clone https://github.com/llvm/llvm-project.git
> + $ cd llvm-project; mkdir build; cd build
> + $ cmake -DLLVM_ENABLE_PROJECTS=clang -DLLVM_TARGETS_TO_BUILD="BPF;X86" -G "Unix Makefiles" ../llvm
>    $ make -j $(getconf _NPROCESSORS_ONLN)

Thanks for the patch. Indeed llvm.org/git/llvm has been deprecated. We 
have recommended to use llvm-project at 
kernel/Documentation/bpf/bpf_devel_QA.rst.
 
https://github.com/torvalds/linux/blob/master/Documentation/bpf/bpf_devel_QA.rst#q-got-it-so-how-do-i-build-llvm-manually-anyway

Could you use the same scripts in the above link here?
There are different ways to build llvm/clang, I just want to be
consistent between bpf_devel_QA.rst and there.

I am also thinking whether we should just provide a link here to
bpf_devel_QA.rst. Looking at samples/bpf/README.rst, it all contains
direct commands for people to build/test, so copy-pasting the llvm
build scripts here should be fine.

>   
>   It is also possible to point make to the newly compiled 'llc' or
>