From 98bd0a06dc4f6c921dc22d3e55ad281db922ce5f Mon Sep 17 00:00:00 2001
From: Alexander Alekhin <alexander.a.alekhin@gmail.com>
Date: Tue, 30 Jan 2018 18:29:18 +0000
Subject: [PATCH 1/2] cmake: fix gnu.toolchain

- CMAKE_FIND_ROOT_PATH_MODE_PROGRAM: ONLY => NEVER
- update handling of CMAKE_FIND_ROOT_PATH_MODE_* variables
---
 platforms/linux/gnu.toolchain.cmake | 60 +++++++++++++++++++++--------
 1 file changed, 45 insertions(+), 15 deletions(-)

diff --git a/platforms/linux/gnu.toolchain.cmake b/platforms/linux/gnu.toolchain.cmake
index 4050d83f61..fc53dbf9f1 100644
--- a/platforms/linux/gnu.toolchain.cmake
+++ b/platforms/linux/gnu.toolchain.cmake
@@ -57,15 +57,51 @@ else()
 endif() # IN_TRY_COMPILE
 
 set(CMAKE_SKIP_RPATH TRUE)
-set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
-set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM ONLY)
+
+if(NOT CMAKE_FIND_ROOT_PATH_MODE_LIBRARY)
+  set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
+endif()
+
+if(NOT CMAKE_FIND_ROOT_PATH_MODE_INCLUDE)
+  set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+endif()
+
+if(NOT CMAKE_FIND_ROOT_PATH_MODE_PACKAGE)
+  set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
+endif()
+
+if(NOT CMAKE_FIND_ROOT_PATH_MODE_PROGRAM)
+  set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
+endif()
+
+macro(__cmake_find_root_save_and_reset)
+  foreach(v
+      CMAKE_FIND_ROOT_PATH_MODE_LIBRARY
+      CMAKE_FIND_ROOT_PATH_MODE_INCLUDE
+      CMAKE_FIND_ROOT_PATH_MODE_PACKAGE
+      CMAKE_FIND_ROOT_PATH_MODE_PROGRAM
+  )
+    set(__save_${v} ${${v}})
+    set(${v} NEVER)
+  endforeach()
+endmacro()
+
+macro(__cmake_find_root_restore)
+  foreach(v
+      CMAKE_FIND_ROOT_PATH_MODE_LIBRARY
+      CMAKE_FIND_ROOT_PATH_MODE_INCLUDE
+      CMAKE_FIND_ROOT_PATH_MODE_PACKAGE
+      CMAKE_FIND_ROOT_PATH_MODE_PROGRAM
+  )
+    set(${v} ${__save_${v}})
+    unset(__save_${v})
+  endforeach()
+endmacro()
+
 
 # macro to find programs on the host OS
 macro(find_host_program)
- set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
- set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY NEVER)
- set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE NEVER)
+ __cmake_find_root_save_and_reset()
  if(CMAKE_HOST_WIN32)
   SET(WIN32 1)
   SET(UNIX)
@@ -77,16 +113,12 @@ macro(find_host_program)
  SET(WIN32)
  SET(APPLE)
  SET(UNIX 1)
- set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM ONLY)
- set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
- set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+ __cmake_find_root_restore()
 endmacro()
 
 # macro to find packages on the host OS
 macro(find_host_package)
- set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
- set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY NEVER)
- set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE NEVER)
+ __cmake_find_root_save_and_reset()
  if(CMAKE_HOST_WIN32)
   SET(WIN32 1)
   SET(UNIX)
@@ -98,9 +130,7 @@ macro(find_host_package)
  SET(WIN32)
  SET(APPLE)
  SET(UNIX 1)
- set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM ONLY)
- set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
- set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+ __cmake_find_root_restore()
 endmacro()
 
 set(CMAKE_SKIP_RPATH TRUE CACHE BOOL "If set, runtime paths are not added when using shared libraries.")

From c4f9ff0285130bd8bcf9d87a9ea6949bdd7e9e5d Mon Sep 17 00:00:00 2001
From: Alexander Alekhin <alexander.alekhin@intel.com>
Date: Wed, 31 Jan 2018 16:56:24 +0300
Subject: [PATCH 2/2] cmake: avoid using of pkg-config in cross-compilation
 mode unconditionally

- specify PKG_CONFIG_LIBDIR environment variable to new target SYSROOT
---
 CMakeLists.txt | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0262cd3a97..77378a1b29 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -552,8 +552,22 @@ endif(WIN32 AND NOT MINGW)
 #       CHECK FOR SYSTEM LIBRARIES, OPTIONS, ETC..
 # ----------------------------------------------------------------------------
 if(UNIX)
-  if(NOT APPLE_FRAMEWORK)
-    find_package(PkgConfig QUIET)
+  if(NOT APPLE_FRAMEWORK OR OPENCV_ENABLE_PKG_CONFIG)
+    if(CMAKE_CROSSCOMPILING AND NOT DEFINED ENV{PKG_CONFIG_LIBDIR}
+        AND NOT OPENCV_ENABLE_PKG_CONFIG
+    )
+      if(NOT PkgConfig_FOUND)
+        message(STATUS "OpenCV disables pkg-config to avoid using of host libraries. Consider using PKG_CONFIG_LIBDIR to specify target SYSROOT")
+      elseif(OPENCV_SKIP_PKG_CONFIG_WARNING)
+        message(WARNING "pkg-config is enabled in cross-compilation mode without defining of PKG_CONFIG_LIBDIR environment variable. This may lead to misconfigured host-based dependencies.")
+      endif()
+    elseif(OPENCV_DISABLE_PKG_CONFIG)
+      if(PkgConfig_FOUND)
+        message(WARNING "OPENCV_DISABLE_PKG_CONFIG flag has no effect")
+      endif()
+    else()
+      find_package(PkgConfig QUIET)
+    endif()
   endif()
   include(CheckFunctionExists)
   include(CheckIncludeFile)