linux-kernel - Re: [PATCH bpf-next v2] samples/bpf: Update README.rst and Makefile for manually compiling LLVM and clang

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Date:   Tue, 19 Jan 2021 13:58:15 -0800
From:   Fangrui Song <maskray@...gle.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>,
        Nathan Chancellor <natechancellor@...il.com>,
        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>
Subject: Re: [PATCH bpf-next v2] samples/bpf: Update README.rst and Makefile
 for manually compiling LLVM and clang

On 2021-01-19, Tiezhu Yang wrote:
>The current llvm/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out of date.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/clang, the Clang Getting Started page [1] has
>one way. As Yonghong said, it is better to just 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.
>
>[1] https://clang.llvm.org/get_started.html
>
>Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
>Acked-by: Yonghong Song <yhs@...com>
>---
>
>v2: Update the commit message suggested by Yonghong,
>    thank you very much.
>
> samples/bpf/Makefile   |  2 +-
> samples/bpf/README.rst | 17 ++++++++++-------
> 2 files changed, 11 insertions(+), 8 deletions(-)
>
>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..d1be438 100644
>--- a/samples/bpf/README.rst
>+++ b/samples/bpf/README.rst
>@@ -65,17 +65,20 @@ 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"
>- $ make -j $(getconf _NPROCESSORS_ONLN)
>+ $ git clone https://github.com/llvm/llvm-project.git
>+ $ mkdir -p llvm-project/llvm/build/install

llvm-project/llvm/build/install is not used.

>+ $ cd llvm-project/llvm/build
>+ $ cmake .. -G "Ninja" -DLLVM_TARGETS_TO_BUILD="BPF;X86" \
>+            -DLLVM_ENABLE_PROJECTS="clang"    \
>+            -DBUILD_SHARED_LIBS=OFF           \

-DBUILD_SHARED_LIBS=OFF is the default. It can be omitted.

>+            -DCMAKE_BUILD_TYPE=Release        \
>+            -DLLVM_BUILD_RUNTIME=OFF

-DLLVM_BUILD_RUNTIME=OFF can be omitted if none of
compiler-rt/libc++/libc++abi is built.

>+ $ 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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