In my project I need to include different files for different build configurations and thus far I've been unable to find a way to do it via CMake.
My build command looks the following way:
cmake -DCMAKE_CONFIGURATION_TYPES=Debug2017;Debug2018;Debug2019;Release2017;Release2018;Release2019 -G"Visual Studio 14 2015" #and so on
In my CMakeLists.txt I want to have something that looks like:
if ($<$<CONFIG:Debug2017>: )
set (MAYA_DIRECTORY "C:/Program Files/Autodesk/Maya2017" )>
endif()
if ($<$<CONFIG:Debug2018>: )
set (MAYA_DIRECTORY "C:/Program Files/Autodesk/Maya2018" )>
endif()
#and so on; obviously script above don't work. I posted it just as an example of what I want to achieve
variable MAYA_DIRECTORY is used later on to set different other variables that are used for include_directories(…) and link_directories(…) calls.
If there is a way to do this by something other than generator expressions that would also work.
Thanks!
You don't. It is possible for single config generators to use CMAKE_BUILD_TYPE but that strategy fails for for multi-config generators like Visual Studio. This is mixing up what happens at configuration time and build time. The active configuration happens at build time.
Therefore you need a separate MAYA_DIRECTORY for each build config. Then you need to include each Maya into the build (I'm guessing they are external projects or something). Then you need to use a generator expressions to pick which Maya you want to use in the executable.
It would be something like this.
target_include_directories(myApp PRIVATE
$<$<CONFIG:Debug2016>:${MAYA_2016_INCS}>
$<$<CONFIG:Debug2017>:${MAYA_2017_INCS}> )
target_link_libraries(myApp PRIVATE
$<$<CONFIG:Debug2016>:${MAYA_2016_LIBS}>
$<$<CONFIG:Debug2017>:${MAYA_2017_LIBS} )
FYI, If you are creating multiple configuration types you need to seed them properly. That is make sure you create a *_Debug2017 with the debug flags and so on.
I have multiple targets that are being made in a CMake project. Each target has a different linkscript (LD file). How do I write the CMakeLists.txt file to make this happen? This is for an embedded project with C/C++/ASM files.
This is what I have so far. The problem is that LINKER_SCRIPT is defined globally and not per-target.
# add alpha target
add_executable(alpha.elf ${SOURCES})
target_compile_definitions(alpha.elf PUBLIC -DALPHA_DEFINED)
set(LINKER_SCRIPT ${CMAKE_SOURCE_DIR}/Linker/alpha.ld)
# add beta target
add_executable(beta.elf ${SOURCES})
target_compile_definitions(beta.elf PUBLIC -DBETA_DEFINED)
set(LINKER_SCRIPT ${CMAKE_SOURCE_DIR}/Linker/beta.ld)
set(CMAKE_EXE_LINKER_FLAGS
"${CMAKE_EXE_LINKER_FLAGS} -T ${LINKER_SCRIPT}")
The problem is that LINKER_SCRIPT gets overwritten and the last definition is the one used. How can I make this work?
I have tried to define per-target variable using the following, however the output is not as expected. The file gets compiled, however things are not where they should be. For example, the generated HEX file does not start at 0x08000000 which is where it should be defined per the LD file.
set_target_properties(alpha.elf PROPERTIES
CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-Map=${PROJECT_BINARY_DIR}/alpha.elf.map -T ${CMAKE_SOURCE_DIR}/Linker/alpha.ld")
The variable LINKER_SCRIPT is just being over-ridden the second time you set it to a value. It doesn't have global scope but sub-directory / function scope. But like any variable it takes on its latest value.
CMAKE_EXE_LINKER_FLAGS is being used for both targets in this case. Splitting this into separate sub-directories may work but I've never tried it.
There are no per-target variables that I am aware of. set_target_properties is used to set properties. Some properties are known to CMake, but the property CMAKE_EXE_LINKER_FLAGS is not one of them. It should just be ignored when generating the build files.
Try using target_link_options to set per-target property LINK_OPTIONS which is known and the option will show up when linking the executable.
For example target_link_options(alpha.elf PRIVATE -T${CMAKE_SOURCE_DIR}/Linker/alpha.ld). I haven't used it with options that have a space in them so that might be a problem.
To re-link if the linker script changes then refer to this answer:
https://stackoverflow.com/a/42138375/1028434
At the beginning I had a bunch of CMake projects handled separately: each one had its own target for generating documentation called doc. Now I need to wrap all these projects with a super-project: the problem is that super-project compilation fails complaining that exist multiple targets with the same name doc.
The simple solution I thought is to prepend each doc target with the name of the project, but it does not satisfy me.
I would like not to have to use make projectX_doc when compiling a single sub-project and to have a global target make doc for generating the documentation of all projects when compiling super-project.
Are my requests possible? Is there any mechanism to handle target collision?
well each subproject could verify if there are inside a super project with:
if("^${CMAKE_SOURCE_DIR}$" STREQUAL "^${PROJECT_SOURCE_DIR}$")
set(IS_SUBPROJECT FALSE)
else()
set(IS_SUBPROJECT TRUE)
endif()
Thus in your projects CMakeLists.txt you can do:
if (NOT IS_SUBPROJECT)
set(DOC_TGT doc)
else()
set(DOC_TGT ${PROJECT_NAME}_doc)
endif()
add_custom_target(${DOC_TGT} EXCLUDE_FROM_ALL ...
note: you can merge both snippets to avoid IS_SUBPROJECT variable
In your super project CMakeLists.txt:
add_custom_target(doc EXCLUDE_FROM_ALL
DEPENDS projectX_doc projectY_doc...
So when configuring/building each sub project standalone you have
make doc otherwise when you are in your super project target doc become a meta target...
note: You can also use this trick to modify default options etc...
e.g. gflags:
https://github.com/gflags/gflags/blob/master/CMakeLists.txt#L126
https://github.com/gflags/gflags/blob/master/cmake/utils.cmake#L61
https://github.com/gflags/gflags/blob/master/CMakeLists.txt#L163
How "${PROJECT_BINARY_DIR}/CMakeFiles/project.dir/", the place object files resulted from compilation will be placed on, can be un-hardcoded?
Going straightly to the problem, we have some tests that check objects resulted from compilation on harfbuzz cmake and we use a hardcoded string there but that doesn't seem right and I hope some ${} or $<> exist for that.
I'm afraid you're out of luck here. CMake keeps this as an internal implementation detail, by design.
I'd say it's unlikely to change, but if you want to be absolutely future-proof, you could use a workaround of creating a static library out of the object files and then manually unpacking it back into object files (using the appropriate archiver/librarian) as part of the test. If the object files are also used by another target, and linking to that static library wouldn't work for that target, you can make an object library out of the files and then use that in both the original target and the for-test static library.
Here's an example of how you might achieve this workaround:
add_library(MyObjectLib OBJECT src/a.cpp src/b.cpp)
add_executable(Main src/main.cpp $<TARGET_OBJECTS:MyObjectLib>)
add_library(LibForTesting STATIC $<TARGET_OBJECTS:MyObjectLib>)
add_test(
NAME check-static-inits.sh
COMMAND ${PROJECT_SOURCE_DIR}/src/prepare-and-check-static-inits.sh $<TARGET_FILE:LibForTesting>
)
And here's what the script prepare-and-check-static-inits.sh would look like (pseudo-code):
ar -x $1 -o some_dir
./check-static-inits.sh some_dir
Turning my comment into an answer
There is at the moment no variable or generator expression to get the list of object files used for linking a archive or library target.
But you could append compiler/archiver/linker calls with any program/script and utilize CMake's expansion rules inside those calls.
Note: That will only work CMake's Command-Line Build Tool Generators. And the list(APPEND ...) calls only have to be there once in your CMake code after your project() call.
Examples
Generate a symbolic link to <OBJECT_DIR> with <TARGET_NAME>
project(MyLib)
list(
APPEND CMAKE_CXX_ARCHIVE_FINISH
"\"${CMAKE_COMMAND}\" -E create_symlink \"<OBJECT_DIR>\" \"<TARGET_NAME>\""
)
[...]
add_library(MyLib STATIC src/a.cpp src/b.cpp)
Call some program to do something with the <OBJECTS> list (e.g. echo or write to a file)
project(MyExe)
list(
APPEND CMAKE_CXX_LINK_EXECUTABLE
"\"${CMAKE_COMMAND}\" -E echo \"<OBJECTS>\""
)
[...]
add_executable(MyExe main.cpp)
Directly do something after each object file is generated. In your case where you want to call objdump for each object file it would e.g. be:
list(
APPEND CMAKE_CXX_COMPILE_OBJECT
"${CMAKE_OBJDUMP} -t \"<OBJECT>\" > $(notdir <OBJECT>.dump)"
)
Unfortunately there is no expansion rule for "output file name" hence the platform/make specific trick with $(notdir ...).
References
CMAKE_<LANG>_ARCHIVE_FINISH
CMAKE_<LANG>_LINK_EXECUTABLE
CMAKE_<LANG>_COMPILE_OBJECT
How to get path to object files with CMake for both multiconfiguration generator and makefile based ones?
In CMake, the flags for the C++ compiler can be influenced in various ways: setting CMAKE_CXX_FLAGS manually, using add_definitions(), forcing a certain C++ standard, and so forth.
In order to compile a target in the same project with different rules (a precompiled header, in my case), I need to reproduce the exact command that is used to compile files added by a command like add_executable() in this directory.
Reading CMAKE_CXX_FLAGS only returns the value set to it explicitly, CMAKE_CXX_FLAGS_DEBUG and siblings only list default Debug/Release options. There is a special functions to retrieve the flags from add_definitions() and add_compiler_options(), but none seem to be able to return the final command line.
How can I get all flags passed to the compiler into a CMake variable?
To answer my own question: It seems like the only way of getting all compiler flags is to reconstruct them from the various sources. The code I'm working with now is the following (for GCC):
macro (GET_COMPILER_FLAGS TARGET VAR)
if (CMAKE_COMPILER_IS_GNUCXX)
set(COMPILER_FLAGS "")
# Get flags form add_definitions, re-escape quotes
get_target_property(TARGET_DEFS ${TARGET} COMPILE_DEFINITIONS)
get_directory_property(DIRECTORY_DEFS COMPILE_DEFINITIONS)
foreach (DEF ${TARGET_DEFS} ${DIRECTORY_DEFS})
if (DEF)
string(REPLACE "\"" "\\\"" DEF "${DEF}")
list(APPEND COMPILER_FLAGS "-D${DEF}")
endif ()
endforeach ()
# Get flags form include_directories()
get_target_property(TARGET_INCLUDEDIRS ${TARGET} INCLUDE_DIRECTORIES)
foreach (DIR ${TARGET_INCLUDEDIRS})
if (DIR)
list(APPEND COMPILER_FLAGS "-I${DIR}")
endif ()
endforeach ()
# Get build-type specific flags
string(TOUPPER ${CMAKE_BUILD_TYPE} BUILD_TYPE_SUFFIX)
separate_arguments(GLOBAL_FLAGS UNIX_COMMAND
"${CMAKE_CXX_FLAGS} ${CMAKE_CXX_FLAGS_${BUILD_TYPE_SUFFIX}}")
list(APPEND COMPILER_FLAGS ${GLOBAL_FLAGS})
# Add -std= flag if appropriate
get_target_property(STANDARD ${TARGET} CXX_STANDARD)
if ((NOT "${STANDARD}" STREQUAL NOTFOUND) AND (NOT "${STANDARD}" STREQUAL ""))
list(APPEND COMPILER_FLAGS "-std=gnu++${STANDARD}")
endif ()
endif ()
set(${VAR} "${COMPILER_FLAGS}")
endmacro ()
This could be extended to also include options induced by add_compiler_options() and more.
Easiest way is to use make VERBOSE=1 when compiling.
cd my-build-dir
cmake path-to-my-sources
make VERBOSE=1
This will do a single-threaded build, and make will print every shell command it runs just before it runs it. So you'll see output like:
[ 0%] Building CXX object Whatever.cpp.o
<huge scary build command it used to build Whatever.cpp>
There actually is a fairly clean way to do this at compile time using CXX_COMPILER_LAUNCHER:
If you have a script print_args.py
#!/usr/bin/env python
import sys
import argparse
print(" ".join(sys.argv[1:]))
# we need to produce an output file so that the link step does not fail
p = argparse.ArgumentParser()
p.add_argument("-o")
args, _ = p.parse_known_args()
with open(args.o, "w") as f:
f.write("")
You can set the target's properties as follows:
add_library(${TARGET_NAME} ${SOURCES})
set_target_properties(${TARGET_NAME} PROPERTIES
CXX_COMPILER_LAUNCHER
${CMAKE_CURRENT_SOURCE_DIR}/print_args.py
)
# this tells the linker to not actually link. Which would fail because output file is empty
set_target_properties(${TARGET_NAME} PROPERTIES
LINK_FLAGS
-E
)
This will print the exact compilation command at compile time.
Short answer
It's not possible to assign final value of compiler command line to variable in CMake script, working in all use cases.
Long answer
Unfortunately, even solution accepted as answer still not gets all compiler flags. As gets noted in comments, there are Transitive Usage Requirements. It's a modern and proper way to write CMake files, getting more and more popular. Also you may have some compile options defined using generator expressions (they look like variable references but will not expand when needed).
Consider having following example:
add_executable(myexe ...);
target_compile_definitions(myexe PRIVATE "PLATFORM_$<PLATFORM_ID>");
add_library(mylib ...);
target_compile_definitions(mylib INTERFACE USING_MY_LIB);
target_link_libraries(myexe PUBLIC mylib);
If you try to call proposed GET_COMPILER_FLAGS macro with myexe target, you will get resulting output -DPLATFORM_$<PLATFORM_ID> instead of expected -DPLATFORM_Linux -DUSING_MY_LIB.
This is because there are two stages between invoking CMake and getting build system generated:
Processing. At this stage CMake reads and executes commands from cmake script(s), particularly, variable values getting evaluated and assigned. At this moment CMake just collecting all required info and being prepared to generate build system (makefiles).
Generating. CMake uses values of special variables and properties, being left at end of processed scripts to finally decide and form generated output. This is where it constructs final command line for compiler according to its internal algorithm, not avaliable for scripting.
Target properties which might be retrieved at processing stage with get_target_property(...) or get_property(... TARGET ...) aren't complete (even when invoked at the end of script). At generating stage CMake walks through each target dependency tree (recursively) and appends properties values according to transitive usage requirements (PUBLIC and INTERFACE tagged values gets propagated).
Although, there are workarounds, depending on what final result you aiming to achieve. This is possible by applying generator expressions, which allows use final values of properties of any target (defined at processing stage)... but later!
Two general possibilites are avaliable:
Generate any output file based on template, which content contains variable references and/or generator expressions, and defined as either string variable value, or input file. It's not flexible due to very limited support of conditional logic (i.e. you cannot use complex concatenations available only with nested foreach() loops), but has advantages, that no further actions required and content described in platform-independent way. Use file(GENERATE ...) command variant. Note, that it behaves differently from file (WRITE ...) variant.
Add custom target (and/or custom command) which implements further usage of expanded value. It's platform dependent and requires user to additionally invoke make (either with some special target, or include to all target), but has advantage, that it's flexible enough because you may implement shell script (but without executable bit).
Example demonstrating solution with combining these options:
set(target_name "myexe")
file(GENERATE OUTPUT script.sh CONTENT "#!/bin/sh\n echo \"${target_name} compile definitions: $<TARGET_PROPERTY:${target_name},COMPILE_DEFINITIONS>\"")
add_custom_target(mycustomtarget
COMMAND echo "\"Platform: $<PLATFORM_ID>\""
COMMAND /bin/sh -s < script.sh
)
After calling CMake build directory will contain file script.sh and invoking make mycustomtarget will print to console:
Platform: Linux
myexe compile definitions: PLATFORM_Linux USING_MY_LIB
Use
set(CMAKE_EXPORT_COMPILE_COMMANDS true)
and get compile_commands.json