bpf, docs: Update build procedure for manually compiling LLVM and Clang

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out of date.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.

At last, we recommend that developers who want the fastest incremental
builds use the Ninja build system [1], you can find it in your system's
package manager, usually the package is ninja or ninja-build [3], so add
ninja to build dependencies suggested by Nathan.

  [1] https://clang.llvm.org/get_started.html
  [2] https://www.llvm.org/docs/CMake.html
  [3] https://github.com/ninja-build/ninja/wiki/Pre-built-Ninja-packages

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Cc: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/bpf/1611279584-26047-1-git-send-email-yangtiezhu@loongson.cn

diff --git a/Documentation/bpf/bpf_devel_QA.rst b/Documentation/bpf/bpf_devel_QA.rst
index 5b613d2a5f1a1fcec5635ad8546f3538897fff5e..2ed89abbf9a4131b24d81cbd62d2467ab0483247 100644 (file)
--- a/Documentation/bpf/bpf_devel_QA.rst
+++ b/Documentation/bpf/bpf_devel_QA.rst
@@ -501,16 +501,19 @@ All LLVM releases can be found at: http://releases.llvm.org/
 
 Q: Got it, so how do I build LLVM manually anyway?
 --------------------------------------------------
-A: You need cmake and gcc-c++ as build requisites for LLVM. Once you have
-that set up, proceed with building the latest LLVM and clang version
+A: We recommend that developers who want the fastest incremental builds
+use the Ninja build system, you can find it in your system's package
+manager, usually the package is ninja or ninja-build.
+
+You need ninja, cmake and gcc-c++ as build requisites for LLVM. Once you
+have 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 26fc96ca619e10271e641959e6dcd7ebd9b433e9..d06144613ca206cd189027823e7432f4d94611af 100644 (file)
--- 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 dd34b2d26f1c70ceb30c160b6c2b5e1bcd06f78b..60c6494adb1b08bc1f244b559339f0caede13e33 100644 (file)
--- a/samples/bpf/README.rst
+++ b/samples/bpf/README.rst
@@ -62,20 +62,26 @@ To generate a smaller llc binary one can use::
 
  -DLLVM_TARGETS_TO_BUILD="BPF"
 
+We recommend that developers who want the fastest incremental builds
+use the Ninja build system, you can find it in your system's package
+manager, usually the package is ninja or ninja-build.
+
 Quick sniplet for manually compiling LLVM and clang
-(build dependencies are cmake and gcc-c++)::
+(build dependencies are ninja, 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
+ $ 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
 -----------------------