Build failue while cross-compiling

[Bidski]

When cross compiling, the linux_resource_linker is not an executable binary on the build system. Is it possible to split this out into a separate repository/project to make it simpler to build this binary on the build system?

[woshiyifei]

Hi @Bidski !
I have some questions:

Do you mean that when cross compiling, we cannot build executable on the fly and then use it ?

To solve this issue, we need to build the executable (linux_resource_linker) first, and the invoke it during the compilation of the main project (opencl-clang) ?

[Bidski]

Hi @woshiyifei

Yes, that is correct. You would need to compile it with the host compiler targetting the host system (the host compiler and the build compiler may not be the same thing)

[anujm1]

You can still build and install opencl-clang natively first and then build the target opencl-clang, no? Yocto does that.

[Bidski]

Of course this is an option, but it seems quite excessive to build all of LLVM for the host just so we can have a host version of linux_resource_linker and then to build all of LLVM a second time for the target.

[woshiyifei]

If implement in opencl-clang, it requires much efforts to implement and also increase the maintain efforts, it also includes efforts for other uses of opencl-clang. The current implementation of linux_resource_linker is reasonable, we need to consider carefully before making change.
I suggest we evaluate the efforts for the other solution and make decisions then.

[Bidski]

Something like this would probably do the trick. If cmake is in cross-compiling mode then build linux_resource linker as an external project (cmake should default to the host compiler in this case). If cmake is not in cross-compiling mode then just add the subdirectory as normal.

This needs testing, but I don't see this as requiring a lot of effort either in terms of implementation or in terms of maintenance.

You could also add HOST_CXX_COMPILER (or similar) so that the user can control which compiler is used to build host targets (also HOST_CXX_FLAGS, etc)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b8b514e..ab38eda 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -55,7 +55,23 @@ include(AddLLVM)
 include(TableGen)
 
 if (NOT WIN32)
-    add_subdirectory( linux_linker )
+    if (CMAKE_CROSSCOMPILING)
+        set(_genlinker "linux_resource_linker${CMAKE_EXECUTABLE_SUFFIX}")
+        add_custom_command(
+            OUTPUT ${_genlinker}
+            COMMAND ${CMAKE_COMMAND} 
+                        -DCMAKE_BUILD_TYPE:STRING="Release"
+                        -DCMAKE_RUNTIME_OUTPUT_DIRECTORY_RELEASE:PATH="${CMAKE_BINARY_DIR}"
+                        -B"bin"
+                        -H"${CMAKE_SOURCE_DIR}/linux_linker"
+            COMMAND ${CMAKE_COMMAND} --build bin --config Release
+        )
+    else()
+        set(_genlinker linux_resource_linker)
+        add_subdirectory(linux_linker)
+    endif()
 endif()
 
 if (CMAKE_SIZEOF_VOID_P EQUAL 4)
diff --git a/linux_linker/CMakeLists.txt b/linux_linker/CMakeLists.txt
index 800e709..78d7ed7 100644
--- a/linux_linker/CMakeLists.txt
+++ b/linux_linker/CMakeLists.txt
@@ -1 +1,4 @@
+CMAKE_MINIMUM_REQUIRED(VERSION 3.4.3)
+PROJECT(linux_linker)
+
 ADD_EXECUTABLE(linux_resource_linker linux_resource_linker)