Add example commands for building perf with Clang.

Since recent Android NDK releases use Clang as the default compiler, a
separate Android specific document is no longer needed; point to the
general build documentation instead.

Signed-off-by: Leo Yan <leo.yan@arm.com>
---
 tools/perf/Documentation/Build.txt   | 18 ++++++++
 tools/perf/Documentation/android.txt | 82 ++++--------------------------------
 2 files changed, 26 insertions(+), 74 deletions(-)

diff --git a/tools/perf/Documentation/Build.txt b/tools/perf/Documentation/Build.txt
index 83dc87c662b63ecc17553a15cc15a6b8d6f01d83..3e4104e605ac0d7d30b4408ef413cf1f90b034c1 100644
--- a/tools/perf/Documentation/Build.txt
+++ b/tools/perf/Documentation/Build.txt
@@ -99,3 +99,21 @@ configuration paths for cross building:
 In this case, the variable PKG_CONFIG_SYSROOT_DIR can be used alongside the
 variable PKG_CONFIG_LIBDIR or PKG_CONFIG_PATH to prepend the sysroot path to
 the library paths for cross compilation.
+
+5) Build with clang
+===================
+By default, the makefile uses GCC as compiler. With specifying environment
+variables HOSTCC, CC and CXX, it allows to build perf with clang.
+
+Using clang for native build:
+
+  $ HOSTCC=clang CC=clang CXX=clang++ make -C tools/perf
+
+Using clang for cross compilation:
+
+  $ HOSTCC=clang CC=clang CXX=clang++ \
+    make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- -C tools/perf \
+    NO_LIBELF=1 NO_LIBTRACEEVENT=1 NO_JEVENTS=1
+
+In the example above, due to lack libelf, python and libtraceevent for
+cross comiplation, disable the features accordingly.
diff --git a/tools/perf/Documentation/android.txt b/tools/perf/Documentation/android.txt
index 24a59998fc91e814ad96f658d3481d88d798b60c..e65204cf2921f6bd8a79875784c5b3d5487ce05d 100644
--- a/tools/perf/Documentation/android.txt
+++ b/tools/perf/Documentation/android.txt
@@ -1,78 +1,12 @@
 How to compile perf for Android
-=========================================
+===============================
 
-I. Set the Android NDK environment
-------------------------------------------------
+There have two ways to build perf and run it on Android.
 
-(a). Use the Android NDK
-------------------------------------------------
-1. You need to download and install the Android Native Development Kit (NDK).
-Set the NDK variable to point to the path where you installed the NDK:
-  export NDK=/path/to/android-ndk
+- The first method is to build perf with static linking, please refer to
+  Build.txt, section "4) Cross compilation" for how to build a static
+  perf binary.
 
-2. Set cross-compiling environment variables for NDK toolchain and sysroot.
-For arm:
-  export NDK_TOOLCHAIN=${NDK}/toolchains/arm-linux-androideabi-4.9/prebuilt/linux-x86_64/bin/arm-linux-androideabi-
-  export NDK_SYSROOT=${NDK}/platforms/android-24/arch-arm
-For x86:
-  export NDK_TOOLCHAIN=${NDK}/toolchains/x86-4.9/prebuilt/linux-x86_64/bin/i686-linux-android-
-  export NDK_SYSROOT=${NDK}/platforms/android-24/arch-x86
-
-This method is only tested for Android NDK versions Revision 11b and later.
-perf uses some bionic enhancements that are not included in prior NDK versions.
-You can use method (b) described below instead.
-
-(b). Use the Android source tree
------------------------------------------------
-1. Download the master branch of the Android source tree.
-Set the environment for the target you want using:
-  source build/envsetup.sh
-  lunch
-
-2. Build your own NDK sysroot to contain latest bionic changes and set the
-NDK sysroot environment variable.
-  cd ${ANDROID_BUILD_TOP}/ndk
-For arm:
-  ./build/tools/build-ndk-sysroot.sh --abi=arm
-  export NDK_SYSROOT=${ANDROID_BUILD_TOP}/ndk/build/platforms/android-3/arch-arm
-For x86:
-  ./build/tools/build-ndk-sysroot.sh --abi=x86
-  export NDK_SYSROOT=${ANDROID_BUILD_TOP}/ndk/build/platforms/android-3/arch-x86
-
-3. Set the NDK toolchain environment variable.
-For arm:
-  export NDK_TOOLCHAIN=${ANDROID_TOOLCHAIN}/arm-linux-androideabi-
-For x86:
-  export NDK_TOOLCHAIN=${ANDROID_TOOLCHAIN}/i686-linux-android-
-
-II. Compile perf for Android
-------------------------------------------------
-You need to run make with the NDK toolchain and sysroot defined above:
-For arm:
-  make WERROR=0 ARCH=arm CROSS_COMPILE=${NDK_TOOLCHAIN} EXTRA_CFLAGS="-pie --sysroot=${NDK_SYSROOT}"
-For x86:
-  make WERROR=0 ARCH=x86 CROSS_COMPILE=${NDK_TOOLCHAIN} EXTRA_CFLAGS="-pie --sysroot=${NDK_SYSROOT}"
-
-III. Install perf
------------------------------------------------
-You need to connect to your Android device/emulator using adb.
-Install perf using:
-  adb push perf /data/perf
-
-If you also want to use perf-archive you need busybox tools for Android.
-For installing perf-archive, you first need to replace #!/bin/bash with #!/system/bin/sh:
-  sed 's/#!\/bin\/bash/#!\/system\/bin\/sh/g' perf-archive >> /tmp/perf-archive
-  chmod +x /tmp/perf-archive
-  adb push /tmp/perf-archive /data/perf-archive
-
-IV. Environment settings for running perf
-------------------------------------------------
-Some perf features need environment variables to run properly.
-You need to set these before running perf on the target:
-  adb shell
-  # PERF_PAGER=cat
-
-IV. Run perf
-------------------------------------------------
-Run perf on your device/emulator to which you previously connected using adb:
-  # ./data/perf
+- The second method is to download Android NDK, then use the contained
+  clang compiler for building perf. Please refer to Build.txt, section
+  "5) Build with clang" for details.

-- 
2.34.1