2021-01-19 05:54:22

by Tiezhu Yang

Subject: [PATCH bpf] samples/bpf: Update README.rst and Makefile for manually compiling LLVM and clang

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may be out of date, they are unable to access: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

There are different ways to build llvm/clang, I find 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 <[email protected]>
---
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
+ $ 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

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

2021-01-19 07:02:58

by Yonghong Song

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

On 1/18/21 7:53 PM, 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:

Let us just rephrase the above more clearly, something like below.

The current clang/llvm 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.
[followed by your descriptions below]

> There are different ways to build llvm/clang, I find 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 <[email protected]>

Ack with minor nits in the above. Also, this is a documentation update.
I think it is okay to target the patch to bpf-next instead of bpf.

Acked-by: Yonghong Song <[email protected]>