From ea08eeccae9297f7aabd2ef7f0c2517ac4549acc Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:18:26 +0000
Subject: [PATCH] write in 30M

---
 kernel/samples/bpf/README.rst |   49 +++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/kernel/samples/bpf/README.rst b/kernel/samples/bpf/README.rst
index 5f27e4f..dd34b2d 100644
--- a/kernel/samples/bpf/README.rst
+++ b/kernel/samples/bpf/README.rst
@@ -14,6 +14,20 @@
 Note that LLVM's tool 'llc' must support target 'bpf', list version
 and supported targets with command: ``llc --version``
 
+Clean and configuration
+-----------------------
+
+It can be needed to clean tools, samples or kernel before trying new arch or
+after some changes (on demand)::
+
+ make -C tools clean
+ make -C samples/bpf clean
+ make clean
+
+Configure kernel, defconfig for instance::
+
+ make defconfig
+
 Kernel headers
 --------------
 
@@ -32,12 +46,10 @@
 For building the BPF samples, issue the below command from the kernel
 top level directory::
 
- make samples/bpf/
-
-Do notice the "/" slash after the directory name.
+ make M=samples/bpf
 
 It is also possible to call make from this directory.  This will just
-hide the the invocation of make as above with the appended "/".
+hide the invocation of make as above.
 
 Manually compiling LLVM with 'bpf' support
 ------------------------------------------
@@ -63,14 +75,31 @@
 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 samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
+ make M=samples/bpf LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
 
 Cross compiling samples
 -----------------------
 In order to cross-compile, say for arm64 targets, export CROSS_COMPILE and ARCH
-environment variables before calling make. This will direct make to build
-samples for the cross target.
+environment variables before calling make. But do this before clean,
+cofiguration and header install steps described above. This will direct make to
+build samples for the cross target::
 
-export ARCH=arm64
-export CROSS_COMPILE="aarch64-linux-gnu-"
-make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
+ export ARCH=arm64
+ export CROSS_COMPILE="aarch64-linux-gnu-"
+
+Headers can be also installed on RFS of target board if need to keep them in
+sync (not necessarily and it creates a local "usr/include" directory also)::
+
+ make INSTALL_HDR_PATH=~/some_sysroot/usr headers_install
+
+Pointing LLC and CLANG is not necessarily if it's installed on HOST and have
+in its targets appropriate arm64 arch (usually it has several arches).
+Build samples::
+
+ make M=samples/bpf
+
+Or build samples with SYSROOT if some header or library is absent in toolchain,
+say libelf, providing address to file system containing headers and libs,
+can be RFS of target board::
+
+ make M=samples/bpf SYSROOT=~/some_sysroot

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