[PATCH v1 4/4] perf augmented_raw_syscalls: Document clang configuration

[Leo Yan <leo.yan@linaro.org>]

To build this program successfully with clang, there have three
compiler options need to be specified:

  - Header file path: tools/perf/include/bpf;
  - Specify architecture;
  - Define macro __NR_CPUS__.

This patch add comments to explain the reasons for building failure and
give two examples for llvm.clang-opt variable, one is for x86_64
architecture and another is for aarch64 architecture.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 .../examples/bpf/augmented_raw_syscalls.c     | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/perf/examples/bpf/augmented_raw_syscalls.c b/tools/perf/examples/bpf/augmented_raw_syscalls.c
index f4ed101b697d..5adc0b3bb351 100644
--- a/tools/perf/examples/bpf/augmented_raw_syscalls.c
+++ b/tools/perf/examples/bpf/augmented_raw_syscalls.c
@@ -6,6 +6,25 @@
  *
  * perf trace -e tools/perf/examples/bpf/augmented_raw_syscalls.c cat /etc/passwd > /dev/null
  *
+ * This program include two header files 'unistd.h' and 'pid_filter.h', which
+ * are placed in the folder tools/perf/include/bpf, but this folder is not
+ * included in env $KERNEL_INC_OPTIONS and it leads to compilation failure.
+ * For building this code, we also need to specify architecture and define macro
+ * __NR_CPUS__.  To resolve these issues, variable llvm.clang-opt can be set in
+ * the file ~/.perfconfig:
+ *
+ * E.g. Test on a platform with 8 CPUs with x86_64 architecture:
+ *
+ *   [llvm]
+ *		clang-opt = "-D__NR_CPUS__=8 -D__x86_64__ \
+ *			     -I./tools/perf/include/bpf"
+ *
+ * E.g. Test on a platform with 5 CPUs with aarch64 architecture:
+ *
+ *   [llvm]
+ *		clang-opt = "-D__NR_CPUS__=5 -D__aarch64__ \
+ *			     -I./tools/perf/include/bpf"
+
  * This exactly matches what is marshalled into the raw_syscall:sys_enter
  * payload expected by the 'perf trace' beautifiers.
  *
-- 
2.17.1