Provided by: cmake-data_3.22.1-1ubuntu1.22.04.2_all 
NAME
cmake-toolchains - CMake Toolchains Reference
INTRODUCTION
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. In normal builds, CMake automatically determines the toolchain for host
builds based on system introspection and defaults. In cross-compiling scenarios, a
toolchain file may be specified with information about compiler and utility paths.
LANGUAGES
Languages are enabled by the project() command. Language-specific built-in variables,
such as CMAKE_CXX_COMPILER, CMAKE_CXX_COMPILER_ID etc are set by invoking the project()
command. If no project command is in the top-level CMakeLists file, one will be
implicitly generated. By default the enabled languages are C and CXX:
project(C_Only C)
A special value of NONE can also be used with the project() command to enable no
languages:
project(MyProject NONE)
The enable_language() command can be used to enable languages after the project() command:
enable_language(CXX)
When a language is enabled, CMake finds a compiler for that language, and determines some
information, such as the vendor and version of the compiler, the target architecture and
bitwidth, the location of corresponding utilities etc.
The ENABLED_LANGUAGES global property contains the languages which are currently enabled.
VARIABLES AND PROPERTIES
Several variables relate to the language components of a toolchain which are enabled.
CMAKE_<LANG>_COMPILER is the full path to the compiler used for <LANG>.
CMAKE_<LANG>_COMPILER_ID is the identifier used by CMake for the compiler and
CMAKE_<LANG>_COMPILER_VERSION is the version of the compiler.
The CMAKE_<LANG>_FLAGS variables and the configuration-specific equivalents contain flags
that will be added to the compile command when compiling a file of a particular language.
As the linker is invoked by the compiler driver, CMake needs a way to determine which
compiler to use to invoke the linker. This is calculated by the LANGUAGE of source files
in the target, and in the case of static libraries, the language of the dependent
libraries. The choice CMake makes may be overridden with the LINKER_LANGUAGE target
property.
TOOLCHAIN FEATURES
CMake provides the try_compile() command and wrapper macros such as
CheckCXXSourceCompiles, CheckCXXSymbolExists and CheckIncludeFile to test capability and
availability of various toolchain features. These APIs test the toolchain in some way and
cache the result so that the test does not have to be performed again the next time CMake
runs.
Some toolchain features have built-in handling in CMake, and do not require compile-tests.
For example, POSITION_INDEPENDENT_CODE allows specifying that a target should be built as
position-independent code, if the compiler supports that feature. The
<LANG>_VISIBILITY_PRESET and VISIBILITY_INLINES_HIDDEN target properties add flags for
hidden visibility, if supported by the compiler.
CROSS COMPILING
If cmake(1) 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.
Note that using the CMAKE_SOURCE_DIR or CMAKE_BINARY_DIR variables inside a toolchain file
is typically undesirable. The toolchain file is used in contexts where these variables
have different values when used in different places (e.g. as part of a call to
try_compile()). In most cases, where there is a need to evaluate paths inside a toolchain
file, the more appropriate variable to use would be CMAKE_CURRENT_LIST_DIR, since it
always has an unambiguous, predictable value.
Cross Compiling for Linux
A typical cross-compiling toolchain for Linux has content such as:
set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)
set(CMAKE_SYSROOT /home/devel/rasp-pi-rootfs)
set(CMAKE_STAGING_PREFIX /home/devel/stage)
set(tools /home/devel/gcc-4.7-linaro-rpi-gnueabihf)
set(CMAKE_C_COMPILER ${tools}/bin/arm-linux-gnueabihf-gcc)
set(CMAKE_CXX_COMPILER ${tools}/bin/arm-linux-gnueabihf-g++)
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)
The CMAKE_SYSTEM_NAME is the CMake-identifier of the target platform to build for.
The CMAKE_SYSTEM_PROCESSOR is the CMake-identifier of the target architecture to build
for.
The CMAKE_SYSROOT is optional, and may be specified if a sysroot is available.
The CMAKE_STAGING_PREFIX is also optional. It may be used to specify a path on the host to
install to. The CMAKE_INSTALL_PREFIX is always the runtime installation location, even
when cross-compiling.
The CMAKE_<LANG>_COMPILER variables may be set to full paths, or to names of compilers to
search for in standard locations. For toolchains that do not support linking binaries
without custom flags or scripts one may set the CMAKE_TRY_COMPILE_TARGET_TYPE variable to
STATIC_LIBRARY to tell CMake not to try to link executables during its checks.
CMake find_* commands will look in the sysroot, and the CMAKE_FIND_ROOT_PATH entries by
default in all cases, as well as looking in the host system root prefix. Although this
can be controlled on a case-by-case basis, when cross-compiling, it can be useful to
exclude looking in either the host or the target for particular artifacts. Generally,
includes, libraries and packages should be found in the target system prefixes, whereas
executables which must be run as part of the build should be found only on the host and
not on the target. This is the purpose of the CMAKE_FIND_ROOT_PATH_MODE_* variables.
Cross Compiling for the Cray Linux Environment
Cross compiling for compute nodes in the Cray Linux Environment can be done without
needing a separate toolchain file. Specifying -DCMAKE_SYSTEM_NAME=CrayLinuxEnvironment on
the CMake command line will ensure that the appropriate build settings and search paths
are configured. The platform will pull its configuration from the current environment
variables and will configure a project to use the compiler wrappers from the Cray
Programming Environment's PrgEnv-* modules if present and loaded.
The default configuration of the Cray Programming Environment is to only support static
libraries. This can be overridden and shared libraries enabled by setting the
CRAYPE_LINK_TYPE environment variable to dynamic.
Running CMake without specifying CMAKE_SYSTEM_NAME will run the configure step in host
mode assuming a standard Linux environment. If not overridden, the PrgEnv-* compiler
wrappers will end up getting used, which if targeting the either the login node or compute
node, is likely not the desired behavior. The exception to this would be if you are
building directly on a NID instead of cross-compiling from a login node. If trying to
build software for a login node, you will need to either first unload the currently loaded
PrgEnv-* module or explicitly tell CMake to use the system compilers in /usr/bin instead
of the Cray wrappers. If instead targeting a compute node is desired, just specify the
CMAKE_SYSTEM_NAME as mentioned above.
Cross Compiling using Clang
Some compilers such as Clang are inherently cross compilers. The
CMAKE_<LANG>_COMPILER_TARGET can be set to pass a value to those supported compilers when
compiling:
set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)
set(triple arm-linux-gnueabihf)
set(CMAKE_C_COMPILER clang)
set(CMAKE_C_COMPILER_TARGET ${triple})
set(CMAKE_CXX_COMPILER clang++)
set(CMAKE_CXX_COMPILER_TARGET ${triple})
Similarly, some compilers do not ship their own supplementary utilities such as linkers,
but provide a way to specify the location of the external toolchain which will be used by
the compiler driver. The CMAKE_<LANG>_COMPILER_EXTERNAL_TOOLCHAIN variable can be set in a
toolchain file to pass the path to the compiler driver.
Cross Compiling for QNX
As the Clang compiler the QNX QCC compile is inherently a cross compiler. And the
CMAKE_<LANG>_COMPILER_TARGET can be set to pass a value to those supported compilers when
compiling:
set(CMAKE_SYSTEM_NAME QNX)
set(arch gcc_ntoarmv7le)
set(CMAKE_C_COMPILER qcc)
set(CMAKE_C_COMPILER_TARGET ${arch})
set(CMAKE_CXX_COMPILER QCC)
set(CMAKE_CXX_COMPILER_TARGET ${arch})
set(CMAKE_SYSROOT $ENV{QNX_TARGET})
Cross Compiling for Windows CE
Cross compiling for Windows CE requires the corresponding SDK being installed on your
system. These SDKs are usually installed under C:/Program Files (x86)/Windows CE
Tools/SDKs.
A toolchain file to configure a Visual Studio generator for Windows CE may look like this:
set(CMAKE_SYSTEM_NAME WindowsCE)
set(CMAKE_SYSTEM_VERSION 8.0)
set(CMAKE_SYSTEM_PROCESSOR arm)
set(CMAKE_GENERATOR_TOOLSET CE800) # Can be omitted for 8.0
set(CMAKE_GENERATOR_PLATFORM SDK_AM335X_SK_WEC2013_V310)
The CMAKE_GENERATOR_PLATFORM tells the generator which SDK to use. Further
CMAKE_SYSTEM_VERSION tells the generator what version of Windows CE to use. Currently
version 8.0 (Windows Embedded Compact 2013) is supported out of the box. Other versions
may require one to set CMAKE_GENERATOR_TOOLSET to the correct value.
Cross Compiling for Windows 10 Universal Applications
A toolchain file to configure a Visual Studio generator for a Windows 10 Universal
Application may look like this:
set(CMAKE_SYSTEM_NAME WindowsStore)
set(CMAKE_SYSTEM_VERSION 10.0)
A Windows 10 Universal Application targets both Windows Store and Windows Phone. Specify
the CMAKE_SYSTEM_VERSION variable to be 10.0 to build with the latest available Windows 10
SDK. Specify a more specific version (e.g. 10.0.10240.0 for RTM) to build with the
corresponding SDK.
Cross Compiling for Windows Phone
A toolchain file to configure a Visual Studio generator for Windows Phone may look like
this:
set(CMAKE_SYSTEM_NAME WindowsPhone)
set(CMAKE_SYSTEM_VERSION 8.1)
Cross Compiling for Windows Store
A toolchain file to configure a Visual Studio generator for Windows Store may look like
this:
set(CMAKE_SYSTEM_NAME WindowsStore)
set(CMAKE_SYSTEM_VERSION 8.1)
Cross Compiling for Android
A toolchain file may configure cross-compiling for Android by setting the
CMAKE_SYSTEM_NAME variable to Android. Further configuration is specific to the Android
development environment to be used.
For Visual Studio Generators, CMake expects NVIDIA Nsight Tegra Visual Studio Edition or
the Visual Studio tools for Android to be installed. See those sections for further
configuration details.
For Makefile Generators and the Ninja generator, CMake expects one of these environments:
• NDK
• Standalone Toolchain
CMake uses the following steps to select one of the environments:
• If the CMAKE_ANDROID_NDK variable is set, the NDK at the specified location will be
used.
• Else, if the CMAKE_ANDROID_STANDALONE_TOOLCHAIN variable is set, the Standalone
Toolchain at the specified location will be used.
• Else, if the CMAKE_SYSROOT variable is set to a directory of the form
<ndk>/platforms/android-<api>/arch-<arch>, the <ndk> part will be used as the value of
CMAKE_ANDROID_NDK and the NDK will be used.
• Else, if the CMAKE_SYSROOT variable is set to a directory of the form
<standalone-toolchain>/sysroot, the <standalone-toolchain> part will be used as the
value of CMAKE_ANDROID_STANDALONE_TOOLCHAIN and the Standalone Toolchain will be used.
• Else, if a cmake variable ANDROID_NDK is set it will be used as the value of
CMAKE_ANDROID_NDK, and the NDK will be used.
• Else, if a cmake variable ANDROID_STANDALONE_TOOLCHAIN is set, it will be used as the
value of CMAKE_ANDROID_STANDALONE_TOOLCHAIN, and the Standalone Toolchain will be used.
• Else, if an environment variable ANDROID_NDK_ROOT or ANDROID_NDK is set, it will be used
as the value of CMAKE_ANDROID_NDK, and the NDK will be used.
• Else, if an environment variable ANDROID_STANDALONE_TOOLCHAIN is set then it will be
used as the value of CMAKE_ANDROID_STANDALONE_TOOLCHAIN, and the Standalone Toolchain
will be used.
• Else, an error diagnostic will be issued that neither the NDK or Standalone Toolchain
can be found.
New in version 3.20: If an Android NDK is selected, its version number is reported in the
CMAKE_ANDROID_NDK_VERSION variable.
Cross Compiling for Android with the NDK
A toolchain file may configure Makefile Generators, Ninja Generators, or Visual Studio
Generators to target Android for cross-compiling.
Configure use of an Android NDK with the following variables:
CMAKE_SYSTEM_NAME
Set to Android. Must be specified to enable cross compiling for Android.
CMAKE_SYSTEM_VERSION
Set to the Android API level. If not specified, the value is determined as
follows:
• If the CMAKE_ANDROID_API variable is set, its value is used as the API level.
• If the CMAKE_SYSROOT variable is set, the API level is detected from the NDK
directory structure containing the sysroot.
• Otherwise, the latest API level available in the NDK is used.
CMAKE_ANDROID_ARCH_ABI
Set to the Android ABI (architecture). If not specified, this variable will
default to the first supported ABI in the list of armeabi, armeabi-v7a and
arm64-v8a. The CMAKE_ANDROID_ARCH variable will be computed from
CMAKE_ANDROID_ARCH_ABI automatically. Also see the CMAKE_ANDROID_ARM_MODE and
CMAKE_ANDROID_ARM_NEON variables.
CMAKE_ANDROID_NDK
Set to the absolute path to the Android NDK root directory. If not specified, a
default for this variable will be chosen as specified above.
CMAKE_ANDROID_NDK_DEPRECATED_HEADERS
Set to a true value to use the deprecated per-api-level headers instead of the
unified headers. If not specified, the default will be false unless using a NDK
that does not provide unified headers.
CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION
On NDK r19 or above, this variable must be unset or set to clang. On NDK r18 or
below, set this to the version of the NDK toolchain to be selected as the compiler.
If not specified, the default will be the latest available GCC toolchain.
CMAKE_ANDROID_STL_TYPE
Set to specify which C++ standard library to use. If not specified, a default will
be selected as described in the variable documentation.
The following variables will be computed and provided automatically:
CMAKE_<LANG>_ANDROID_TOOLCHAIN_PREFIX
The absolute path prefix to the binutils in the NDK toolchain.
CMAKE_<LANG>_ANDROID_TOOLCHAIN_SUFFIX
The host platform suffix of the binutils in the NDK toolchain.
For example, a toolchain file might contain:
set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_SYSTEM_VERSION 21) # API level
set(CMAKE_ANDROID_ARCH_ABI arm64-v8a)
set(CMAKE_ANDROID_NDK /path/to/android-ndk)
set(CMAKE_ANDROID_STL_TYPE gnustl_static)
Alternatively one may specify the values without a toolchain file:
$ cmake ../src \
-DCMAKE_SYSTEM_NAME=Android \
-DCMAKE_SYSTEM_VERSION=21 \
-DCMAKE_ANDROID_ARCH_ABI=arm64-v8a \
-DCMAKE_ANDROID_NDK=/path/to/android-ndk \
-DCMAKE_ANDROID_STL_TYPE=gnustl_static
Cross Compiling for Android with a Standalone Toolchain
A toolchain file may configure Makefile Generators or the Ninja generator to target
Android for cross-compiling using a standalone toolchain.
Configure use of an Android standalone toolchain with the following variables:
CMAKE_SYSTEM_NAME
Set to Android. Must be specified to enable cross compiling for Android.
CMAKE_ANDROID_STANDALONE_TOOLCHAIN
Set to the absolute path to the standalone toolchain root directory. A
${CMAKE_ANDROID_STANDALONE_TOOLCHAIN}/sysroot directory must exist. If not
specified, a default for this variable will be chosen as specified above.
CMAKE_ANDROID_ARM_MODE
When the standalone toolchain targets ARM, optionally set this to ON to target
32-bit ARM instead of 16-bit Thumb. See variable documentation for details.
CMAKE_ANDROID_ARM_NEON
When the standalone toolchain targets ARM v7, optionally set thisto ON to target
ARM NEON devices. See variable documentation for details.
The following variables will be computed and provided automatically:
CMAKE_SYSTEM_VERSION
The Android API level detected from the standalone toolchain.
CMAKE_ANDROID_ARCH_ABI
The Android ABI detected from the standalone toolchain.
CMAKE_<LANG>_ANDROID_TOOLCHAIN_PREFIX
The absolute path prefix to the binutils in the standalone toolchain.
CMAKE_<LANG>_ANDROID_TOOLCHAIN_SUFFIX
The host platform suffix of the binutils in the standalone toolchain.
For example, a toolchain file might contain:
set(CMAKE_SYSTEM_NAME Android)
set(CMAKE_ANDROID_STANDALONE_TOOLCHAIN /path/to/android-toolchain)
Alternatively one may specify the values without a toolchain file:
$ cmake ../src \
-DCMAKE_SYSTEM_NAME=Android \
-DCMAKE_ANDROID_STANDALONE_TOOLCHAIN=/path/to/android-toolchain
Cross Compiling for Android with NVIDIA Nsight Tegra Visual Studio Edition
A toolchain file to configure one of the Visual Studio Generators to build using NVIDIA
Nsight Tegra targeting Android may look like this:
set(CMAKE_SYSTEM_NAME Android)
The CMAKE_GENERATOR_TOOLSET may be set to select the Nsight Tegra "Toolchain Version"
value.
See also target properties:
• ANDROID_ANT_ADDITIONAL_OPTIONS
• ANDROID_API_MIN
• ANDROID_API
• ANDROID_ARCH
• ANDROID_ASSETS_DIRECTORIES
• ANDROID_GUI
• ANDROID_JAR_DEPENDENCIES
• ANDROID_JAR_DIRECTORIES
• ANDROID_JAVA_SOURCE_DIR
• ANDROID_NATIVE_LIB_DEPENDENCIES
• ANDROID_NATIVE_LIB_DIRECTORIES
• ANDROID_PROCESS_MAX
• ANDROID_PROGUARD_CONFIG_PATH
• ANDROID_PROGUARD
• ANDROID_SECURE_PROPS_PATH
• ANDROID_SKIP_ANT_STEP
• ANDROID_STL_TYPE
Cross Compiling for iOS, tvOS, or watchOS
For cross-compiling to iOS, tvOS, or watchOS, the Xcode generator is recommended. The
Unix Makefiles or Ninja generators can also be used, but they require the project to
handle more areas like target CPU selection and code signing.
Any of the three systems can be targeted by setting the CMAKE_SYSTEM_NAME variable to a
value from the table below. By default, the latest Device SDK is chosen. As for all
Apple platforms, a different SDK (e.g. a simulator) can be selected by setting the
CMAKE_OSX_SYSROOT variable, although this should rarely be necessary (see Switching
Between Device and Simulator below). A list of available SDKs can be obtained by running
xcodebuild -showsdks.
┌────────┬───────────────────┬─────────────────────┬──────────────────┐
│OS │ CMAKE_SYSTEM_NAME │ Device SDK │ Simulator SDK │
│ │ │ (default) │ │
├────────┼───────────────────┼─────────────────────┼──────────────────┤
│iOS │ iOS │ iphoneos │ iphonesimulator │
├────────┼───────────────────┼─────────────────────┼──────────────────┤
│tvOS │ tvOS │ appletvos │ appletvsimulator │
├────────┼───────────────────┼─────────────────────┼──────────────────┤
│watchOS │ watchOS │ watchos │ watchsimulator │
└────────┴───────────────────┴─────────────────────┴──────────────────┘
For example, to create a CMake configuration for iOS, the following command is sufficient:
cmake .. -GXcode -DCMAKE_SYSTEM_NAME=iOS
Variable CMAKE_OSX_ARCHITECTURES can be used to set architectures for both device and
simulator. Variable CMAKE_OSX_DEPLOYMENT_TARGET can be used to set an iOS/tvOS/watchOS
deployment target.
Next configuration will install fat 5 architectures iOS library and add the
-miphoneos-version-min=9.3/-mios-simulator-version-min=9.3 flags to the compiler:
$ cmake -S. -B_builds -GXcode \
-DCMAKE_SYSTEM_NAME=iOS \
"-DCMAKE_OSX_ARCHITECTURES=armv7;armv7s;arm64;i386;x86_64" \
-DCMAKE_OSX_DEPLOYMENT_TARGET=9.3 \
-DCMAKE_INSTALL_PREFIX=`pwd`/_install \
-DCMAKE_XCODE_ATTRIBUTE_ONLY_ACTIVE_ARCH=NO \
-DCMAKE_IOS_INSTALL_COMBINED=YES
Example:
# CMakeLists.txt
cmake_minimum_required(VERSION 3.14)
project(foo)
add_library(foo foo.cpp)
install(TARGETS foo DESTINATION lib)
Install:
$ cmake --build _builds --config Release --target install
Check library:
$ lipo -info _install/lib/libfoo.a
Architectures in the fat file: _install/lib/libfoo.a are: i386 armv7 armv7s x86_64 arm64
$ otool -l _install/lib/libfoo.a | grep -A2 LC_VERSION_MIN_IPHONEOS
cmd LC_VERSION_MIN_IPHONEOS
cmdsize 16
version 9.3
Code Signing
Some build artifacts for the embedded Apple platforms require mandatory code signing. If
the Xcode generator is being used and code signing is required or desired, the development
team ID can be specified via the CMAKE_XCODE_ATTRIBUTE_DEVELOPMENT_TEAM CMake variable.
This team ID will then be included in the generated Xcode project. By default, CMake
avoids the need for code signing during the internal configuration phase (i.e compiler ID
and feature detection).
Switching Between Device and Simulator
When configuring for any of the embedded platforms, one can target either real devices or
the simulator. Both have their own separate SDK, but CMake only supports specifying a
single SDK for the configuration phase. This means the developer must select one or the
other at configuration time. When using the Xcode generator, this is less of a limitation
because Xcode still allows you to build for either a device or a simulator, even though
configuration was only performed for one of the two. From within the Xcode IDE, builds
are performed for the selected "destination" platform. When building from the command
line, the desired sdk can be specified directly by passing a -sdk option to the underlying
build tool (xcodebuild). For example:
$ cmake --build ... -- -sdk iphonesimulator
Please note that checks made during configuration were performed against the
configure-time SDK and might not hold true for other SDKs. Commands like find_package(),
find_library(), etc. store and use details only for the configured SDK/platform, so they
can be problematic if wanting to switch between device and simulator builds. You can
follow the next rules to make device + simulator configuration work:
• Use explicit -l linker flag, e.g. target_link_libraries(foo PUBLIC "-lz")
• Use explicit -framework linker flag, e.g. target_link_libraries(foo PUBLIC "-framework
CoreFoundation")
• Use find_package() only for libraries installed with CMAKE_IOS_INSTALL_COMBINED feature
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