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

[Yonghong Song <yhs@fb.com>]

On 1/21/21 6:23 AM, Nathan Chancellor wrote:
> On Thu, Jan 21, 2021 at 12:08:31AM -0800, Andrii Nakryiko wrote:
>> On Wed, Jan 20, 2021 at 9:36 PM Nathan Chancellor
>> <natechancellor@gmail.com> wrote:
>>>
>>> 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 out of date.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).
>>
>> it's possible to generate Makefile by passing `-g "Unix Makefiles"`,
>> which would avoid dependency on ninja, no?
> 
> Yes, although I am fairly certain that building with ninja is quicker so
> I would recommend keeping it. One small extra dependency never killed
> anyone plus ninja is becoming more common nowadays :)

Agree. Let us use 'ninja' here, which is widely used in llvm community
for llvm-project build compared to other alternatives.

> 
>>> 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
>>>>