From d7d2a4f7004d7fd64bece1a0f74cdd966bb7e8e0 Mon Sep 17 00:00:00 2001
From: Liu Yiqun <liuyiqun01@baidu.com>
Date: Fri, 28 Apr 2017 06:35:31 +0000
Subject: [PATCH] Add cross-compiling toolchain for Android.

---
 CMakeLists.txt                      |   8 +-
 cmake/cross_compiling/android.cmake | 171 ++++++++++++++++++++++++++++
 cmake/system.cmake                  |  24 +++-
 3 files changed, 194 insertions(+), 9 deletions(-)
 create mode 100644 cmake/cross_compiling/android.cmake

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 624083b2cee..abd07297cb4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,17 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License
 
+cmake_minimum_required(VERSION 3.0)
+
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/cmake")
 set(PROJ_ROOT ${CMAKE_SOURCE_DIR})
 
 include(system)
 
-if(ANDROID)
-    cmake_minimum_required(VERSION 3.7)
-else()
-    cmake_minimum_required(VERSION 3.0)
-endif()
-
 project(paddle CXX C)
 
 find_package(Sphinx)
diff --git a/cmake/cross_compiling/android.cmake b/cmake/cross_compiling/android.cmake
new file mode 100644
index 00000000000..db5a753cd46
--- /dev/null
+++ b/cmake/cross_compiling/android.cmake
@@ -0,0 +1,171 @@
+# Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+# 
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+# 
+# http://www.apache.org/licenses/LICENSE-2.0
+# 
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This is a toolchain file for cross-compiling for Android, and the
+# configuration refers to the open-source resposity:
+#     https://github.com/taka-no-me/android-cmake
+# Most of the variables are compatible with that used in
+#     https://developer.android.com/ndk/guides/cmake.html
+# The supported are listed belows:
+# 
+# ANDROID_STANDALONE_TOOLCHAIN
+# ANDROID_ABI
+# ANDROID_NATIVE_API_LEVEL
+# ANDROID_PLATFORM
+# ANDROID_ARM_MODE
+# ANDROID_ARM_NEON
+#
+# For CMake >= 3.7.0, all the settings will be delivered to CMake system
+# variables to let CMake do the cross-compiling configurations itself.
+# More detail of cross-compiling settings
+#     https://cmake.org/cmake/help/v3.7/manual/cmake-toolchains.7.html
+
+IF(NOT ANDROID)
+    return()
+ENDIF()
+
+# check the exist of android standalone toolchain
+IF(NOT DEFINED ANDROID_STANDALONE_TOOLCHAIN)
+    SET(ANDROID_STANDALONE_TOOLCHAIN $ENV{ANDROID_STANDALONE_TOOLCHAIN}
+        CACHE PATH "Folder holds the standalone toolchain of Android NDK")
+ENDIF()
+IF(NOT ANDROID_STANDALONE_TOOLCHAIN)
+    MESSAGE(FATAL_ERROR "Set ANDROID_STANDALONE_TOOLCHAIN to use a standalone toolchain.\n"
+            "To cross-compile for Android, you need to:\n"
+            "1. Download an Android NDK from"
+            " https://developer.android.com/ndk/downloads/index.html\n"
+            "2. Setup a standalone toolchain"
+            " https://developer.android.google.cn/ndk/guides/standalone_toolchain.html?hl=zh-cn")
+ENDIF()
+
+IF(DEFINED ANDROID_NATIVE_API_LEVEL)
+    IF(ANDROID_NATIVE_API_LEVEL MATCHES "^android-[0-9]+$")
+        STRING(REPLACE "android-" "" CMAKE_SYSTEM_VERSION "${CMAKE_MATCH_0}")
+    ELSEIF(ANDROID_NATIVE_API_LEVEL MATCHES "^[0-9]+$")
+        SET(CMAKE_SYSTEM_VERSION ${ANDROID_NATIVE_API_LEVEL})
+    ENDIF()
+    SET(ANDROID_PLATFORM android-${CMAKE_SYSTEM_VERSION})
+ENDIF()
+
+IF(NOT DEFINED ANDROID_ABI)
+    SET(ANDROID_ABI "armeabi-v7a")
+ENDIF()
+
+IF(NOT DEFINED ANDROID_ARM_MODE)
+    SET(ANDROID_ARM_MODE ON)
+ENDIF()
+
+IF(NOT DEFINED ANDROID_ARM_NEON)
+    SET(ANDROID_ARM_NEON ON)
+ENDIF()
+
+IF(NOT ANDROID_ARM_MODE OR ANDROID_ARM_MODE STREQUAL "thumb")
+    SET(ANDROID_ARM_MODE OFF)
+    SET(ANDROID_ARM_MODE_NAME "thumb")
+ELSEIF(ANDROID_ARM_MODE OR ANDROID_ARM_MODE STREQUAL "arm")
+    SET(ANDROID_ARM_MODE ON)
+    SET(ANDROID_ARM_MODE_NAME "arm")
+ENDIF()
+
+IF(${CMAKE_VERSION} VERSION_LESS "3.7.0")  
+    IF(${CMAKE_VERSION} VERSION_LESS "3.1.0")
+        SET(CMAKE_SYSTEM_NAME "Linux")
+    ENDIF()
+    MESSAGE(WARNING "It is recommended to use CMake >= 3.7.0 (current version: "
+            "${CMAKE_VERSION}), when cross-compiling for Android.")
+
+    SET(CMAKE_SYSROOT "${ANDROID_STANDALONE_TOOLCHAIN}/sysroot")
+
+    IF(NOT CMAKE_SYSTEM_VERSION)
+        SET(ANDROID_STANDALONE_TOOLCHAIN_API "")
+        SET(ANDROID_API_LEVEL_H_REGEX "^[\t ]*#[\t ]*define[\t ]+__ANDROID_API__[\t ]+([0-9]+)")
+        FILE(STRINGS "${ANDROID_STANDALONE_TOOLCHAIN}/sysroot/usr/include/android/api-level.h"
+            ANDROID_API_LEVEL_H_CONTENT REGEX "${ANDROID_API_LEVEL_H_REGEX}")
+        IF(ANDROID_API_LEVEL_H_CONTENT MATCHES "${ANDROID_API_LEVEL_H_REGEX}")
+            SET(ANDROID_STANDALONE_TOOLCHAIN_API "${CMAKE_MATCH_1}")
+        ENDIF()
+        SET(CMAKE_SYSTEM_VERSION ${ANDROID_STANDALONE_TOOLCHAIN_API})
+    ENDIF()
+
+    # Toolchain
+    SET(ANDROID_TOOLCHAIN "gcc")
+    SET(ANDROID_TOOLCHAIN_ROOT ${ANDROID_STANDALONE_TOOLCHAIN})
+    IF(ANDROID_ABI MATCHES "^armeabi(-v7a)?$")
+        SET(ANDROID_TOOLCHAIN_NAME arm-linux-androideabi)
+        IF(ANDROID_ABI STREQUAL "armeabi")
+            SET(CMAKE_SYSTEM_PROCESSOR armv5te)
+        ELSEIF(ANDROID_ABI STREQUAL "armeabi-v7a")
+            SET(CMAKE_SYSTEM_PROCESSOR armv7-a)
+        ENDIF()
+    ENDIF()
+    SET(ANDROID_TOOLCHAIN_PREFIX "${ANDROID_TOOLCHAIN_ROOT}/bin/${ANDROID_TOOLCHAIN_NAME}-")
+     
+    SET(CMAKE_C_COMPILER "${ANDROID_TOOLCHAIN_PREFIX}gcc")
+    SET(CMAKE_CXX_COMPILER "${ANDROID_TOOLCHAIN_PREFIX}g++")
+
+    # Toolchain and ABI specific flags.
+    SET(ANDROID_COMPILER_FLAGS "-ffunction-sections -fdata-sections -finline-limit=64")
+    SET(ANDROID_LINKER_FLAGS "-Wl,--gc-sections")
+
+    IF(ANDROID_ABI STREQUAL "armeabi")
+        LIST(APPEND ANDROID_COMPILER_FLAGS
+             -march=armv5te
+             -mtune=xscale
+             -msoft-float)
+    ENDIF()
+    IF(ANDROID_ABI STREQUAL "armeabi-v7a")
+        LIST(APPEND ANDROID_COMPILER_FLAGS
+             -march=armv7-a
+             -mfloat-abi=softfp)
+        IF(ANDROID_ARM_NEON)
+            LIST(APPEND ANDROID_COMPILER_FLAGS -mfpu=neon)
+        ELSE()
+            LIST(APPEND ANDROID_COMPILER_FLAGS -mfpu=vfpv3-d16)
+        ENDIF()
+        LIST(APPEND ANDROID_LINKER_FLAGS -Wl,--fix-cortex-a8)
+    ENDIF()
+
+    IF(ANDROID_ABI MATCHES "^armeabi(-v7a)?$")
+        IF(ANDROID_ARM_MODE)
+            LIST(APPEND ANDROID_COMPILER_FLAGS -marm)
+        ELSE()
+            LIST(APPEND ANDROID_COMPILER_FLAGS -mthumb)
+        ENDIF()
+    ENDIF()
+
+    STRING(REPLACE ";" " " ANDROID_COMPILER_FLAGS "${ANDROID_COMPILER_FLAGS}")
+    STRING(REPLACE ";" " " ANDROID_LINKER_FLAGS "${ANDROID_LINKER_FLAGS}")
+
+    SET(CMAKE_C_FLAGS "${ANDROID_COMPILER_FLAGS} ${CMAKE_C_FLAGS}"
+        CACHE STRING "c flags")
+    SET(CMAKE_CXX_FLAGS "${ANDROID_COMPILER_FLAGS} ${CMAKE_CXX_FLAGS}"
+        CACHE STRING "c++ flags")
+    SET(CMAKE_SHARED_LINKER_FLAGS "${ANDROID_LINKER_FLAGS} ${CMAKE_SHARED_LINKER_FLAGS}"
+        CACHE STRING "shared linker flags")
+
+    SET(CMAKE_POSITION_INDEPENDENT_CODE TRUE)
+    SET(CMAKE_EXE_LINKER_FLAGS "-pie -fPIE ${ANDROID_LINKER_FLAGS} ${CMAKE_EXE_LINKER_FLAGS}"
+        CACHE STRING "executable linker flags")
+
+    MESSAGE(STATUS "Android: Targeting API '${CMAKE_SYSTEM_VERSION}' "
+            "with architecture '${ANDROID_ARM_MODE_NAME}', "
+            "ABI '${ANDROID_ABI}', and processor '${CMAKE_SYSTEM_PROCESSOR}'")
+    MESSAGE(STATUS "System CMAKE_C_FLAGS: " ${CMAKE_C_FLAGS})
+    MESSAGE(STATUS "System CMAKE_CXX_FLAGS: " ${CMAKE_CXX_FLAGS})
+ELSE()
+    SET(CMAKE_ANDROID_STANDALONE_TOOLCHAIN ${ANDROID_STANDALONE_TOOLCHAIN})
+    SET(CMAKE_ANDROID_ARCH_ABI ${ANDROID_ABI})
+    SET(CMAKE_ANDROID_ARM_MODE ${ANDROID_ARM_MODE})
+    SET(CMAKE_ANDROID_ARM_NEON ${ANDROID_ARM_NEON})
+ENDIF()
diff --git a/cmake/system.cmake b/cmake/system.cmake
index 75a9d8fc256..b34b7436622 100644
--- a/cmake/system.cmake
+++ b/cmake/system.cmake
@@ -13,9 +13,9 @@
 # limitations under the License.
 
 # Detects the OS and sets appropriate variables.
-# CMAKE_SYSTEM_NAME only give us a coarse-grained name,
-# but the name like centos is necessary in some scenes
-# to distinguish system for customization.
+# CMAKE_SYSTEM_NAME only give us a coarse-grained name of the OS CMake is
+# building for, but the host processor name like centos is necessary
+# in some scenes to distinguish system for customization.
 #
 # for instance, protobuf libs path is <install_dir>/lib64
 # on CentOS, but <install_dir>/lib on other systems.
@@ -72,12 +72,30 @@ MARK_AS_ADVANCED(HOST_SYSTEM CPU_CORES)
 MESSAGE(STATUS "Found Paddle host system: ${HOST_SYSTEM}")
 MESSAGE(STATUS "Found Paddle host system's CPU: ${CPU_CORES} cores")
 
+# configuration for cross-compiling
 IF(DEFINED CMAKE_SYSTEM_NAME)
     IF(${CMAKE_SYSTEM_NAME} STREQUAL "Android")
         SET(ANDROID TRUE)
+        INCLUDE(cross_compiling/android)
     ENDIF()
 ENDIF()
 
+# suffix on different os
+IF(WIN32)
+    SET(SHARED_LIBRARY_SUFFIX ".dll")
+    SET(STATIC_LIBRARY_SUFFIX ".lib")
+    SET(EXECUTABLE_SUFFIX ".exe")
+ELSE(WIN32)
+    IF(APPLE)
+        SET(SHARED_LIBRARY_SUFFIX ".dylib")
+    ELSE(APPLE)
+        SET(SHARED_LIBRARY_SUFFIX ".so")
+    ENDIF(APPLE)
+
+    SET(STATIC_LIBRARY_SUFFIX ".a")
+    SET(EXECUTABLE_SUFFIX "")
+ENDIF(WIN32)
+
 # external dependencies log output
 SET(EXTERNAL_PROJECT_LOG_ARGS
     LOG_DOWNLOAD    0     # Wrap download in script to log output
-- 
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