I'm trying to build a multi-project project with cmake, and have used the ExternalProject_Add() command. However, I can't get the CMAKE_CXX_COMPILER option to stick, which causes the following problem: During configure, the external project checks for several compiler capabilities, setting (or not setting, in this case) a necessary flag in a .h file. When I run make, a different compiler is used, and the values in the .h file are incorrect.
I've boiled it down to the following lines of code, which occur at the top of my CMakeLists.txt file for the external project (CGAL):
message("**** CXX Compiler is ${CMAKE_CXX_COMPILER}")
project(CGAL CXX C)
message("**** CXX Compiler is ${CMAKE_CXX_COMPILER}")
When I run this, the first message displays the correct value (the Frameworks compiler installed through XCode). However, the second message shows the wrong compiler (GNU version I've installed with MacPorts). I've looked up the project specifications, but they are quite sparse. They do note that, without including the project() command, an implicit one will be added with the CXX and C languages. Sure enough, when I remove the project() command, both messages report the wrong compiler.
Is there something I don't know about the project() command? Does it search for a CMakeLists.txt file somewhere in the filepath and load it by default? Is there a way I can overload this setting (something short of creating a temporary variable to hold the old value)?
FWIW, setting CMAKE_CACHE_ARGS doesn't work.
Related
I'm wondering how CMake finds the compiler you want to use.
I found that after I called project, the variable CMAKE_CXX_COMPILER_ID is automatically set to GNU. It's sure that when executing cmake command, I gave -DCMAKE_TOOLCHAIN_FILE flag to tell which toolchain file I wanted to use. And in the toolchain file, I specifies CMAKE_C_COMPILER and CMAKE_CXX_COMPILER as arm-none-eabi-gcc, g++.
However, just setting these variables doesn't mean telling CMake what compiler I'm using right?
According to https://cmake.org/cmake/help/latest/variable/CMAKE_LANG_COMPILER.html,
it seems that CMAKE_C_COMPILER or CMAKE_CXX_COMPILER is a so-called cmake-variables, which means CMake can parse the contents and do something based on them.
Does CMake read and understand CMAKE_C_COMPILER and CMAKE_CXX_COMPILER itself, and based on that, CMake automatically sets CMAKE_CXX_COMPILER_ID to GNU or something at the time when project is called?
When CMake first encounters a project() command, the compiler, linker and several properties based on those are "set in stone". Any adjustments before the first project() command can change the compiler cmake chooses, whether you set this via -D command line option, toolchain file or via set() commands in the CMakeLists.txt file. (I strongly recommend not using the last option though, since it limits reuseability.)
If no information was provided, cmake chooses the compiler itself; the exact logic depends on the platform though.
CMAKE_CXX_COMPILER_ID is one of the variables that are set based on the compiler chosen. Basically cmake performs some checks to determine the type of compiler used, the target platform, ect.
I am looking to set various compilers for different folders in my project, which should compile to a shared library.
The project structure is as follows -
/Cuda
a.cu
b.cu
c.cu
header.cuh
/SYCL
a.cpp
b.cpp
c.cpp
header.h
main.cpp
test.cpp
All the files under the Cuda folder must be compiled by nvcc, and the files under the SYCL folder by a specific compiler that is present at a path in the system. All the files outside these folders (namely main.cpp and test.cpp) are normal C++ code and use the headers present in these two folders and must be compiled with GCC.
How do I go about writing the CMake for such a project structure(which aims to be a shared lib).
Edit - The project needn't have only one dedicated CMake. My approach was as follows -
Each Folder(Cuda and SYCL) can have their dedicated CmakeLists.txt which would specify the compiler and the various flags to go with it.
A master CMake outside the folder can use the add_subdirectory command. And this is where I get stuck, I am not sure what to do next, how to link these two folders with the main and the test files.
CMake allows one compiler per language, so simply writing this is enough:
cmake_minimum_required(VERSION 3.20)
project(example LANGUAGES CXX CUDA)
add_subdirectory(Cuda)
add_subdirectory(SYCL)
You can separately set the C++ and CUDA compilers by setting CMAKE_CXX_COMPILER and CMAKE_CUDA_COMPILER at the configure command line.
$ cmake -S . -B build -DCMAKE_BUILD_TYPE=Release \
-DCMAKE_CXX_COMPILER=g++ -DCMAKE_CUDA_COMPILER=nvcc
Also, I want to clear up this misconception:
Each Folder(Cuda and SYCL) can have their dedicated CmakeLists.txt which would specify the compiler and the various flags to go with it.
The CMakeLists.txt file should not attempt to specify the compiler. It's tricky to do correctly, can't always be done (especially in the add_subdirectory case) and unnecessarily restricts your ability to switch out the compiler. Maybe you have both GCC 10 and 11 installed and want to compare the two.
Similarly, you should not specify flags in the CMakeLists.txt file that aren't absolutely required to build, and you should always check the CMake documentation to see if the flags you're interested in have been abstracted for you. For instance, CMake has special handling of the C++ language standard (via target_compile_features) and CUDA separable compilation (via the CUDA_SEPARABLE_COMPILATION target property).
The best solution, as I have detailed here, is to set optional flags via the *_FLAGS* variables in a preset or toolchain.
I would like to use the IAR compiler. I noticed CMake has already have a bunch of files about this compiler:
https://github.com/jevinskie/cmake/blob/master/Modules/Compiler/IAR.cmake
From what I read the common solution is to specify manually ALL the toolchain in my CMakeLists.txt:
set(CMAKE_C_COMPILER iccarm)
set(CMAKE_CPP_COMPILER iccarm)
How CMake can link these definitions with `Modules/Compiler/IAR.cmake"?
I thought I would just have to do
include("Modules/Compiler/IAR.cmake")
What is the correct way to specify my IAR compiler?
When I do
cmake .
It still tries to use gcc instead of my IAR compiler. Why?
To select a specific compiler, you have several solutions, as exaplained in CMake wiki:
Method 1: use environment variables
For C and C++, set the CC and CXX environment variables. This method is not guaranteed to work for all generators. (Specifically, if you are trying to set Xcode's GCC_VERSION, this method confuses Xcode.)
For example:
CC=gcc-4.2 CXX=/usr/bin/g++-4.2 cmake -G "Your Generator" path/to/your/source
Method 2: use cmake -D
Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path on the command-line using cmake -D.
For example:
cmake -G "Your Generator" -D CMAKE_C_COMPILER=gcc-4.2 -D CMAKE_CXX_COMPILER=g++-4.2 path/to/your/source
Method 3 (avoid): use set()
Set the appropriate CMAKE_FOO_COMPILER variable(s) to a valid compiler name or full path in a list file using set(). This must be done before any language is set (ie: before any project() or enable_language() command).
For example:
set(CMAKE_C_COMPILER "gcc-4.2")
set(CMAKE_CXX_COMPILER "/usr/bin/g++-4.2")
project("YourProjectName")
The wiki doesn't provide reason why 3rd method should be avoided...
I see more and more people who set CMAKE_C_COMPILER and other compiler-related variables in the CMakeLists.txt after the project call and wonder why this approach breaks sometimes.
What happens actually
When CMake executes the project() call, it looks for a default compiler executable and determines the way for use it: default compiler flags, default linker flags, compile features, etc.
And CMake stores path to that default compiler executable in the CMAKE_C_COMPILER variable.
When one sets CMAKE_C_COMPILER variable after the project() call, this only changes the compiler executable: default flags, features all remains set for the default compiler.
AS RESULT: When the project is built, a build system calls the project-specified compiler executable but with parameters suitable for the default compiler.
As one could guess, this approach would work only when one replaces a default compiler with a highly compatible one. E.g. replacement of gcc with clang could work sometimes.
This approach will never work for replacement of cl compiler (used in Visual Studio) with gcc one. Nor this will work when replacing a native compiler with a cross-compiler.
What to do
Never set a compiler in CMakeLists.txt.
If you want, e.g., to use clang instead of defaulted gcc, then either:
Pass -DCMAKE_C_COMPILER=<compiler> to cmake when configure the project. That way CMake will use this compiler instead of default one and on the project() call it will adjust all flags for the specified compiler.
Set CC environment variable (CXX for C++ compiler). CMake checks this variable when selects a default compiler.
(Only in rare cases) Set CMAKE_C_COMPILER variable before the project() call. This approach is similar to the first one, but makes the project less flexible.
If the ways above do not work
If on setting CMAKE_C_COMPILER in the command line CMake errors that a compiler cannot "compile a simple project", then something wrong in your environment.. or you specify a compiler incompatible for chosen generator or platform.
Examples:
Visual Studio generators work with cl compiler but cannot work with gcc.
A MinGW compiler usually requires MinGW Makefiles generator.
Incompatible generator cannot be fixed in CMakeLists.txt. One need to pass the proper -G option to the cmake executable (or select the proper generator in CMake GUI).
Cross-compiling
Cross-compiling usually requires setting CMAKE_SYSTEM_NAME variable, and this setting should normally be done in the toolchain file. That toolchain file is also responsible for set a compiler.
Setting CMAKE_SYSTEM_NAME in the CMakeLists.txt is almost always an error.
You need to create a toolchain file, and use the CmakeForceCompiler module.
Here is an example toolchain file for bare-metal ARM development with IAR:
include(CMakeForceCompiler)
set(CMAKE_SYSTEM_NAME Generic) # Or name of your OS if you have one
set(CMAKE_SYSTEM_PROCESSOR arm) # Or whatever
set(CMAKE_CROSSCOMPILING 1)
set(CMAKE_C_COMPILER iccarm) # Change the arm suffix if appropriate
set(CMAKE_TRY_COMPILE_TARGET_TYPE STATIC_LIBRARY) # Required to make the previous line work for a target that requires a custom linker file
The last line is necessary because CMake will try to compile a test program with the compiler to make sure it works and to get some version information from preprocessor defines. Without this line, CMake will use add_executable() for the test program, and you will get the error "The C compiler "XXX" is not able to compile a simple test program." This is because the test program fails to link, as it doesn't have your custom linker file (I'm assuming bare-metal development since this is what IAR is usually used for). This line tells CMake to use add_library() instead, which makes the test succeed without the linker file. Source of this workaround: this CMake mailing list post.
Then, assuming that your toolchain file is named iar-toolchain.cmake, invoke CMake like this:
cmake -DCMAKE_TOOLCHAIN_FILE=iar-toolchain.cmake .
You can call cmake like this:
cmake -DCMAKE_C_COMPILER=iccarm ...
or
cmake -DCMAKE_CXX_COMPILER=...
If you don't want to use your PC's standard compiler, you have to give CMake the path to the compiler. You do this via environment variables, a toolchain file or direct definitions in the CMake command line (see e.g. CMake Error at CMakeLists.txt:30 (project): No CMAKE_C_COMPILER could be found).
Putting the compiler's name/path into your CMakeLists.txt would stop your project from being cross-platform.
CMake does check for the compiler ids by compiling special C/C++ files. So no need to manually include from Module/Compiler or Module/Platform.
This will be automatically done by CMake based on its compiler and platform checks.
References
CMake: In which Order are Files parsed (Cache, Toolchain, …)?
CMake GitLab Commit: Add support files for C, C++ and ASM for the IAR toolchain.
IAR Systems recently published a basic CMake tutorial with examples under their GitHub profile.
I like the the idea of a generic toolchain file which works seamlessly for both Windows and Linux compilers using find_program().
The following snippet will be used for when using C and can be used similarly for CXX:
# IAR C Compiler
find_program(CMAKE_C_COMPILER
NAMES icc${CMAKE_SYSTEM_PROCESSOR}
PATHS ${TOOLKIT}
"$ENV{ProgramFiles}/IAR Systems/*"
"$ENV{ProgramFiles\(x86\)}/IAR Systems/*"
/opt/iarsystems/bx${CMAKE_SYSTEM_PROCESSOR}
PATH_SUFFIXES bin ${CMAKE_SYSTEM_PROCESSOR}/bin
REQUIRED )
For ASM, I initially got puzzled with the NAMES but then I realized that the toolchain file was made that way for working with old Assemblers shipped with XLINK:
find_program(CMAKE_ASM_COMPILER
NAMES iasm${CMAKE_SYSTEM_PROCESSOR} a${CMAKE_SYSTEM_PROCESSOR}
PATHS ${TOOLKIT}
"$ENV{PROGRAMFILES}/IAR Systems/*"
"$ENV{ProgramFiles\(x86\)}/IAR Systems/*"
/opt/iarsystems/bx${CMAKE_SYSTEM_PROCESSOR}
PATH_SUFFIXES bin ${CMAKE_SYSTEM_PROCESSOR}/bin
REQUIRED )
Also, take a look at the full toolchain file. It will work automatically for "Arm" when the tools are installed on their default locations, otherwise it is just about updating the TOOLKIT variable and the compilers for all the supported languages should adjust automatically.
If your wanting to specify a compiler in cmake then just do ...
cmake_minimum_required(VERSION 3.22)
set(CMAKE_C_COMPILER "clang")
set(CMAKE_CXX_COMPILER "clang++")
Options 1 is only used if you want to specify what compiler you want to use as default for everything that you might compile on your computer. And I don't even think it would work on windows.
Option 2 would be used if you only want to use a different temporarily.
Option 3 is used if that's the compiler that should be used for that particular project. Also option 3 would be the most cross compatible.
I have a custom build cmake v3.10.0 which was compiled with a gcc_4.8.3. I am using this custom build cmake to compile a cmake project that must use gcc _4.1.2 because of legacy code.
Executing cmake promted me with an error because it needs to use the libstdc++-IFX.so.6 provided by gcc_4.8.3 which I fixed by adding the path to the correct library in my LD_LIBRARY_PATH before the path to the libraries provided by gcc_4.1.2.
Compiling my project and linking an executable (which is done by c++) results in the linker taking the gcc_4.8.3 stdlibs over the gcc_4.1.2 libs. Is there any way to tell cmake to not use the libraries it needs for himself for my cmake project preferably without touching LD_LIBRARY_PATH?
Edits:
#squareskittles comment: I did read and try everything this post suggest but without any changes. The libstdc++-IFX.so.6 is still taken from gcc_4.8.3
I am attempting to import a manually-created cmake project that I had been using in a different IDE into Netbeans 8.0.2 on Windows 7. Needless to say, my cmake configuration worked fine there.
Netbeans seems to import the directory fine. I imported it in "automatic" (cmake) mode. However, when I attempt to build the project, I get a rather cryptic (Java?) error message:
Makefile:76: recipe for target 'all' failed
process_begin: CreateProcess(NULL, /C/MinGW/bin/make.exe -f CMakeFiles/Makefile2 all, ...) failed.
make (e=2): The system cannot find the file specified.
Knowing very little about Java, I am not sure how to interpret this error. The first directory (/C/MinGW/bin/make.exe) stands out to me as not being in Windows-format, but I am not sure if that's incorrect. I do indeed have a file by that name, as I copied the longer-named mingw make binary so I would only need to type "make".
Presuming this is being run in the project root, and that the first directory is formatted correctly, I don't see any problem with finding these files.
My CMakeLists.txt is:
cmake_minimum_required(VERSION 2.8.4)
set(Project_Name "Test")
set(Test_VERSION_MAJOR 1)
set(Test_VERSION_MINOR 0)
project(${Project_Name})
include_directories(
"${CMAKE_CURRENT_SOURCE_DIR}/inc"
"${CMAKE_CURRENT_SOURCE_DIR}/inc/SDL"
"C:/Users/Bakaiya/Documents/ogre/OgreMain/include"
)
file(GLOB SOURCE_FILES "${CMAKE_CURRENT_SOURCE_DIR}/src/*.cpp")
link_directories(${CMAKE_CURRENT_SOURCE_DIR} ${OPENGL_LIBRARIES})
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
add_executable(${Project_Name} ${SOURCE_FILES})
target_link_libraries(${Project_Name} SDL2main SDL2 OgreMain) #Ogre
Running the "generate makefile" command in the IDE completes without issue, but does not fix the problem. Additionally, clean fails, but "help" does work.
This is a problem within the IDE, it seems, because if I run make from the command line in the project root, it builds without issue.
Also, I fiddled with the file path mode setting under C/C++ -> Project Options, and it did nothing. Even set to absolute, what seems to be a relative path (CMakeFiles/Makefile2) is still in the failed command. I'm not sure if that option is expected to change that sort of reference or not.
What could be wrong with this imported project to cause this issue?
However, when I attempt to build the project, I get a rather cryptic (Java?) error message:
This is an error shown by netbeans to tell you, that it was unable to execute make command successfully. Usually this indicates a wrong setting of your (mingw-) tools.
Here are some points you can check:
Don't use make from mingw/bin, you have to use the one from mingw/msys/... There's a mingw make within mingw's msys folder, usually C:\<Path to MSYS>\<Version>\bin\make.exe - this bin-path must also be set in PATH environment variable! If MSys wasn't installed with your mingw installation, please install it.
Please check the tools set in Tools -> Options -> C/C++ -> Build Tools; you can test them by clicking Versions....
(If existing) Clean the CMake generated files and clean the cmake's cache. If not done yet, please use an out-of-source build as described here.
Can you build your project from terminal (without netbeans)?
The first directory (/C/MinGW/bin/make.exe) stands out to me as not being in Windows-format, but I am not sure if that's incorrect.
This is ok and intended by mingw - it uses linux / unix like paths.
Update
Which make program should I use?
Many MinGW users have a problem because they use mingw32-make.exe from
the MinGW installation. While this seems like the right choice, it
actually breaks the build. The problem is that this is a non-Posix
implementation of the Unix make program and doesn't work well at all.
In fact, thats why the MinGW people renamed it! They've also made a
FAQ entry explaining why you should not use mingw32-make.exe. Instead,
you should use the make.exe program from the MSYS package.
As of NetBeans 6.1, the Build Tools panel no longer allows a user to
select mingw32-make. If you choose a MinGW compiler collection it will
default to make in MSYS. If MSYS is not found, it will tell you no
make program has been found.
(http://wiki.netbeans.org/MinGWInCCDevelopmentPack)