Update cross compile checks and files #2497 (#2564)

3 files changed, 138 insertions, 54 deletions

diff --git a/config/cmake/ConfigureChecks.cmake b/config/cmake/ConfigureChecks.cmake
index ef434b3..14ad0cf 100644
--- a/config/cmake/ConfigureChecks.cmake
+++ b/config/cmake/ConfigureChecks.cmake
@@ -770,56 +770,57 @@ if (HDF5_BUILD_FORTRAN)
     set (${HDF_PREFIX}_SIZEOF__QUAD ${_SIZEOF__QUAD})
   endif ()
 
-#-----------------------------------------------------------------------------
-# The provided CMake C macros don't provide a general compile/run function
-# so this one is used.
-#-----------------------------------------------------------------------------
-  set (RUN_OUTPUT_PATH_DEFAULT ${CMAKE_BINARY_DIR})
-  macro (C_RUN FUNCTION_NAME SOURCE_CODE RETURN_VAR RETURN_OUTPUT_VAR)
-      message (VERBOSE "Detecting C ${FUNCTION_NAME}")
-      file (WRITE
-          ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testCCompiler1.c
-          ${SOURCE_CODE}
-      )
-      TRY_RUN (RUN_RESULT_VAR COMPILE_RESULT_VAR
-          ${CMAKE_BINARY_DIR}
-          ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testCCompiler1.c
-          COMPILE_DEFINITIONS "-D_SIZEOF___FLOAT128=${H5_SIZEOF___FLOAT128};-D_HAVE_QUADMATH_H=${H5_HAVE_QUADMATH_H}"
-          COMPILE_OUTPUT_VARIABLE COMPILEOUT
-          RUN_OUTPUT_VARIABLE OUTPUT_VAR
-      )
+  if (NOT CMAKE_CROSSCOMPILING)
+    #-----------------------------------------------------------------------------
+    # The provided CMake C macros don't provide a general compile/run function
+    # so this one is used.
+    #-----------------------------------------------------------------------------
+    set (RUN_OUTPUT_PATH_DEFAULT ${CMAKE_BINARY_DIR})
+    macro (C_RUN FUNCTION_NAME SOURCE_CODE RETURN_VAR RETURN_OUTPUT_VAR)
+        message (VERBOSE "Detecting C ${FUNCTION_NAME}")
+        file (WRITE
+            ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testCCompiler1.c
+            ${SOURCE_CODE}
+        )
+        TRY_RUN (RUN_RESULT_VAR COMPILE_RESULT_VAR
+            ${CMAKE_BINARY_DIR}
+            ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/testCCompiler1.c
+            COMPILE_DEFINITIONS "-D_SIZEOF___FLOAT128=${H5_SIZEOF___FLOAT128};-D_HAVE_QUADMATH_H=${H5_HAVE_QUADMATH_H}"
+            COMPILE_OUTPUT_VARIABLE COMPILEOUT
+            RUN_OUTPUT_VARIABLE OUTPUT_VAR
+        )
 
-      set (${RETURN_OUTPUT_VAR} ${OUTPUT_VAR})
-
-      message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
-      message (VERBOSE "Test COMPILE_RESULT_VAR ${COMPILE_RESULT_VAR} ")
-      message (VERBOSE "Test COMPILE_OUTPUT ${COMPILEOUT} ")
-      message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
-      message (VERBOSE "Test RUN_RESULT_VAR ${RUN_RESULT_VAR} ")
-      message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
-
-      if (COMPILE_RESULT_VAR)
-        if (RUN_RESULT_VAR EQUAL "0")
-          set (${RETURN_VAR} 1 CACHE INTERNAL "Have C function ${FUNCTION_NAME}")
-          message (VERBOSE "Testing C ${FUNCTION_NAME} - OK")
-          file (APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
-              "Determining if the C ${FUNCTION_NAME} exists passed with the following output:\n"
-              "${OUTPUT_VAR}\n\n"
-          )
+        set (${RETURN_OUTPUT_VAR} ${OUTPUT_VAR})
+
+        message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
+        message (VERBOSE "Test COMPILE_RESULT_VAR ${COMPILE_RESULT_VAR} ")
+        message (VERBOSE "Test COMPILE_OUTPUT ${COMPILEOUT} ")
+        message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
+        message (VERBOSE "Test RUN_RESULT_VAR ${RUN_RESULT_VAR} ")
+        message (VERBOSE "* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ")
+
+        if (COMPILE_RESULT_VAR)
+          if (RUN_RESULT_VAR EQUAL "0")
+            set (${RETURN_VAR} 1 CACHE INTERNAL "Have C function ${FUNCTION_NAME}")
+            message (VERBOSE "Testing C ${FUNCTION_NAME} - OK")
+            file (APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeOutput.log
+                "Determining if the C ${FUNCTION_NAME} exists passed with the following output:\n"
+                "${OUTPUT_VAR}\n\n"
+            )
+          else ()
+            message (VERBOSE "Testing C ${FUNCTION_NAME} - Fail")
+            set (${RETURN_VAR} 0 CACHE INTERNAL "Have C function ${FUNCTION_NAME}")
+            file (APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
+                "Determining if the C ${FUNCTION_NAME} exists failed with the following output:\n"
+                "${OUTPUT_VAR}\n\n")
+          endif ()
         else ()
-          message (VERBOSE "Testing C ${FUNCTION_NAME} - Fail")
-          set (${RETURN_VAR} 0 CACHE INTERNAL "Have C function ${FUNCTION_NAME}")
-          file (APPEND ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeError.log
-              "Determining if the C ${FUNCTION_NAME} exists failed with the following output:\n"
-              "${OUTPUT_VAR}\n\n")
+            message (FATAL_ERROR "Compilation of C ${FUNCTION_NAME} - Failed")
         endif ()
-      else ()
-          message (FATAL_ERROR "Compilation of C ${FUNCTION_NAME} - Failed")
-      endif ()
-  endmacro ()
+    endmacro ()
 
-  set (PROG_SRC
-      "
+    set (PROG_SRC
+        "
 #include <float.h>\n\
 #include <stdio.h>\n\
 #define CHECK_FLOAT128 _SIZEOF___FLOAT128\n\
@@ -840,17 +841,18 @@ if (HDF5_BUILD_FORTRAN)
 #else\n\
 #define C_LDBL_DIG LDBL_DIG\n\
 #endif\n\nint main() {\nprintf(\"\\%d\\\;\\%d\\\;\", C_LDBL_DIG, C_FLT128_DIG)\\\;\n\nreturn 0\\\;\n}\n
-       "
-  )
+         "
+    )
 
-  C_RUN ("maximum decimal precision for C" ${PROG_SRC} PROG_RES PROG_OUTPUT4)
-  message (STATUS "Testing maximum decimal precision for C - ${PROG_OUTPUT4}")
+    C_RUN ("maximum decimal precision for C" ${PROG_SRC} PROG_RES PROG_OUTPUT4)
+    message (STATUS "Testing maximum decimal precision for C - ${PROG_OUTPUT4}")
 
-  # dnl The output from the above program will be:
-  # dnl  -- long double decimal precision  --  __float128 decimal precision
+    # dnl The output from the above program will be:
+    # dnl  -- long double decimal precision  --  __float128 decimal precision
 
-  list (GET PROG_OUTPUT4 0 H5_LDBL_DIG)
-  list (GET PROG_OUTPUT4 1 H5_FLT128_DIG)
+    list (GET PROG_OUTPUT4 0 H5_LDBL_DIG)
+    list (GET PROG_OUTPUT4 1 H5_FLT128_DIG)
+  endif ()
 
   if (${HDF_PREFIX}_SIZEOF___FLOAT128 EQUAL "0" OR FLT128_DIG EQUAL "0")
     set (${HDF_PREFIX}_HAVE_FLOAT128 0)
diff --git a/config/toolchain/aarch64.cmake b/config/toolchain/aarch64.cmake
index 03f4e5e..6996833 100644
--- a/config/toolchain/aarch64.cmake
+++ b/config/toolchain/aarch64.cmake
@@ -11,6 +11,7 @@ set (CMAKE_FIND_ROOT_PATH /usr/${TOOLCHAIN_PREFIX})
 set (CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
 set (CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
 set (CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
+set (CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)
 set (CMAKE_CROSSCOMPILING_EMULATOR qemu-aarch64)
 
 include_directories(/usr/${TOOLCHAIN_PREFIX}/include)
diff --git a/release_docs/INSTALL_CMake.txt b/release_docs/INSTALL_CMake.txt
index c98a3d9..b5521f8 100644
--- a/release_docs/INSTALL_CMake.txt
+++ b/release_docs/INSTALL_CMake.txt
@@ -13,6 +13,7 @@ Section V:    Options for building HDF5 Libraries with CMake command line
 Section VI:   CMake option defaults for HDF5
 Section VII:  User Defined Options for HDF5 Libraries with CMake
 Section VIII: User Defined Compile Flags for HDF5 Libraries with CMake
+Section IX:   Considerations for cross-compiling
 
 ************************************************************************
 
@@ -939,6 +940,86 @@ to CMAKE_C_FLAGS.
 
 
 ========================================================================
+IX:   Considerations for cross-compiling
+========================================================================
+
+Cross-compiling has several consequences for CMake:
+    CMake cannot automatically detect the target platform.
+    CMake cannot find libraries and headers in the default system directories.
+    Executables built during cross compiling cannot be executed.
+
+Cross-compiling support means that CMake separates information about the
+build platform and target platform and gives the user mechanisms to solve
+cross-compiling issues without additional requirements such as running
+virtual machines, etc.
+
+CMake uses a toolchain of utilities to compile, link libraries and create
+archives, and other tasks to drive the build. The toolchain utilities
+available are determined by the languages enabled.
+
+CMake stores info about the current toolchain in the following variables:
+    CMAKE_C_COMPILER,
+    CMAKE_CXX_COMPILER.
+They contain paths to the C and C++ compilers respectively. This is usually
+enough on desktop platforms. In the case of embedded systems, a custom
+linker and assembler setting may be needed. In more complex projects
+you may need to additionally specify binaries to other parts of the toolchain
+(size, ranlib, objcopy…). All these tools should be set in the corresponding
+variables:
+    CMAKE_AR,
+    CMAKE_ASM_COMPILER,
+    CMAKE_LINKER,
+    CMAKE_OBJCOPY,
+    CMAKE_RANLIB
+
+As for the host and target operating systems, CMake stores their names in the
+following variables:
+    CMAKE_HOST_SYSTEM_NAME – name of the platform, on which CMake is running (host platform).
+        On major operating systems this is set to the Linux, Windows or
+        Darwin (MacOS) value.
+    CMAKE_SYSTEM_NAME – name of the platform, for which we are building (target platform).
+        By default, this value is the same as CMAKE_HOST_SYSTEM_NAME, which
+        means that we are building for the local platform (no cross-compilation).
+
+Put the toolchain variables into a separate file (e.g. <toolchain_name>.cmake)
+and set CMAKE_TOOLCHAIN_FILE variable to the path of that file.
+If cmake is invoked with the command line parameter:
+    --toolchain path/to/file
+or
+    -DCMAKE_TOOLCHAIN_FILE=path/to/file
+the file will be loaded early to set values for the compilers. The
+CMAKE_CROSSCOMPILING variable is set to true when CMake is cross-compiling.
+
+Structure of the toolchain file
+-------------------------------
+In fact, the toolchain file doesn’t have any structure. You can put anything you
+want there. But the best practice is to define at least these settings:
+path to the toolchain binaries (C compiler, C++ compiler, linker, etc.)
+name of the target platform (and optionally target processor architecture)
+required compilation and linking flags on that particular platform
+toolchain sysroot settings
+
+It is recommended that you set the CMAKE_FIND_ROOT_PATH variable to a path where
+you have an exact copy of the root filesystem you have on your target device (with
+libraries and binaries pre-compiled for the target processor).
+
+References:
+    https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html
+    https://gitlab.com/embeddedlinux/libs/platform
+    https://discourse.cmake.org/t/cross-compile-for-aarch64-on-ubuntu/2161/10
+    https://stackoverflow.com/questions/54539682/how-to-set-up-cmake-to-cross-compile-with-clang-for-arm-embedded-on-windows?rq=1
+    https://developer.android.com/ndk/guides/cmake
+
+Predefine H5Tinit.c file
+-------------------------------
+The one file that needs to be pre-generated is the H5Tinit.c file. The variables
+indicated in the error log (see above) are the variables that need to match the target system.
+
+The HDF5 CMake variables;
+    HDF5_USE_PREGEN: set this to true
+    HDF5_USE_PREGEN_DIR: set this path to the preset H5Tinit.c file
+
+========================================================================
 For further assistance, send email to help@hdfgroup.org
 ========================================================================