[PATCH] samples: bpf: fix outdated README build command

["Daniel T. Lee" <danieltimlee@gmail.com>]

Currently, building the bpf samples under samples/bpf directory isn't
working. Running make from the directory 'samples/bpf' will just shows
following result without compiling any samples.

 $ make
 make -C ../../ /git/linux/samples/bpf/ BPF_SAMPLES_PATH=/git/linux/samples/bpf
 make[1]: Entering directory '/git/linux'
   CALL    scripts/checksyscalls.sh
   CALL    scripts/atomic/check-atomics.sh
   DESCEND  objtool
 make[1]: Leaving directory '/git/linux'

Due to commit 394053f4a4b3 ("kbuild: make single targets work more
correctly"), building samples/bpf without support of samples/Makefile
is unavailable. Instead, building the samples with 'make M=samples/bpf'
from the root source directory will solve this issue.[1]

This commit fixes the outdated README build command with samples/bpf.

[0]: https://patchwork.kernel.org/patch/11168393/

Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
---
 samples/bpf/README.rst | 19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

diff --git a/samples/bpf/README.rst b/samples/bpf/README.rst
index 5f27e4faca50..bfd2405705ed 100644
--- a/samples/bpf/README.rst
+++ b/samples/bpf/README.rst
@@ -32,12 +32,10 @@ Compiling
 For building the BPF samples, issue the below command from the kernel
 top level directory::
 
- make samples/bpf/
+ make M=samples/bpf
 
-Do notice the "/" slash after the directory name.
-
-It is also possible to call make from this directory.  This will just
-hide the the invocation of make as above with the appended "/".
+Due to samples/bpf cannot be built without support in the
+samples/Makefile, it is unavailable to call make from this directory.
 
 Manually compiling LLVM with 'bpf' support
 ------------------------------------------
@@ -63,14 +61,15 @@ Quick sniplet for manually compiling LLVM and clang
 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.
+samples for the cross target.::
+
+ export ARCH=arm64
+ export CROSS_COMPILE="aarch64-linux-gnu-"
+ make M=samples/bpf LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
 
-export ARCH=arm64
-export CROSS_COMPILE="aarch64-linux-gnu-"
-make samples/bpf/ LLC=~/git/llvm/build/bin/llc CLANG=~/git/llvm/build/bin/clang
-- 
2.20.1