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

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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out of date.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@xxxxxxxxxxx>
Acked-by: Yonghong Song <yhs@xxxxxx>
---

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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