149 lines
4.9 KiB
Markdown
149 lines
4.9 KiB
Markdown
## Using GoogleTest from various build systems
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GoogleTest comes with pkg-config files that can be used to determine all
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necessary flags for compiling and linking to GoogleTest (and GoogleMock).
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Pkg-config is a standardised plain-text format containing
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* the includedir (-I) path
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* necessary macro (-D) definitions
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* further required flags (-pthread)
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* the library (-L) path
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* the library (-l) to link to
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All current build systems support pkg-config in one way or another. For all
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examples here we assume you want to compile the sample
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`samples/sample3_unittest.cc`.
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### CMake
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Using `pkg-config` in CMake is fairly easy:
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```cmake
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cmake_minimum_required(VERSION 3.0)
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cmake_policy(SET CMP0048 NEW)
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project(my_gtest_pkgconfig VERSION 0.0.1 LANGUAGES CXX)
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find_package(PkgConfig)
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pkg_search_module(GTEST REQUIRED gtest_main)
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add_executable(testapp samples/sample3_unittest.cc)
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target_link_libraries(testapp ${GTEST_LDFLAGS})
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target_compile_options(testapp PUBLIC ${GTEST_CFLAGS})
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include(CTest)
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add_test(first_and_only_test testapp)
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```
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It is generally recommended that you use `target_compile_options` + `_CFLAGS`
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over `target_include_directories` + `_INCLUDE_DIRS` as the former includes not
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just -I flags (GoogleTest might require a macro indicating to internal headers
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that all libraries have been compiled with threading enabled. In addition,
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GoogleTest might also require `-pthread` in the compiling step, and as such
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splitting the pkg-config `Cflags` variable into include dirs and macros for
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`target_compile_definitions()` might still miss this). The same recommendation
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goes for using `_LDFLAGS` over the more commonplace `_LIBRARIES`, which happens
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to discard `-L` flags and `-pthread`.
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### Help! pkg-config can't find GoogleTest!
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Let's say you have a `CMakeLists.txt` along the lines of the one in this
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tutorial and you try to run `cmake`. It is very possible that you get a failure
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along the lines of:
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```
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-- Checking for one of the modules 'gtest_main'
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CMake Error at /usr/share/cmake/Modules/FindPkgConfig.cmake:640 (message):
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None of the required 'gtest_main' found
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```
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These failures are common if you installed GoogleTest yourself and have not
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sourced it from a distro or other package manager. If so, you need to tell
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pkg-config where it can find the `.pc` files containing the information. Say you
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installed GoogleTest to `/usr/local`, then it might be that the `.pc` files are
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installed under `/usr/local/lib64/pkgconfig`. If you set
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```
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export PKG_CONFIG_PATH=/usr/local/lib64/pkgconfig
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```
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pkg-config will also try to look in `PKG_CONFIG_PATH` to find `gtest_main.pc`.
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### Using pkg-config in a cross-compilation setting
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Pkg-config can be used in a cross-compilation setting too. To do this, let's
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assume the final prefix of the cross-compiled installation will be `/usr`, and
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your sysroot is `/home/MYUSER/sysroot`. Configure and install GTest using
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```
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mkdir build && cmake -DCMAKE_INSTALL_PREFIX=/usr ..
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```
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Install into the sysroot using `DESTDIR`:
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```
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make -j install DESTDIR=/home/MYUSER/sysroot
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```
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Before we continue, it is recommended to **always** define the following two
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variables for pkg-config in a cross-compilation setting:
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```
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export PKG_CONFIG_ALLOW_SYSTEM_CFLAGS=yes
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export PKG_CONFIG_ALLOW_SYSTEM_LIBS=yes
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```
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otherwise `pkg-config` will filter `-I` and `-L` flags against standard prefixes
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such as `/usr` (see https://bugs.freedesktop.org/show_bug.cgi?id=28264#c3 for
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reasons why this stripping needs to occur usually).
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If you look at the generated pkg-config file, it will look something like
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```
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libdir=/usr/lib64
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includedir=/usr/include
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Name: gtest
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Description: GoogleTest (without main() function)
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Version: 1.10.0
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URL: https://github.com/google/googletest
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Libs: -L${libdir} -lgtest -lpthread
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Cflags: -I${includedir} -DGTEST_HAS_PTHREAD=1 -lpthread
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```
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Notice that the sysroot is not included in `libdir` and `includedir`! If you try
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to run `pkg-config` with the correct
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`PKG_CONFIG_LIBDIR=/home/MYUSER/sysroot/usr/lib64/pkgconfig` against this `.pc`
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file, you will get
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```
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$ pkg-config --cflags gtest
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-DGTEST_HAS_PTHREAD=1 -lpthread -I/usr/include
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$ pkg-config --libs gtest
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-L/usr/lib64 -lgtest -lpthread
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```
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which is obviously wrong and points to the `CBUILD` and not `CHOST` root. In
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order to use this in a cross-compilation setting, we need to tell pkg-config to
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inject the actual sysroot into `-I` and `-L` variables. Let us now tell
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pkg-config about the actual sysroot
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```
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export PKG_CONFIG_DIR=
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export PKG_CONFIG_SYSROOT_DIR=/home/MYUSER/sysroot
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export PKG_CONFIG_LIBDIR=${PKG_CONFIG_SYSROOT_DIR}/usr/lib64/pkgconfig
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```
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and running `pkg-config` again we get
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```
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$ pkg-config --cflags gtest
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-DGTEST_HAS_PTHREAD=1 -lpthread -I/home/MYUSER/sysroot/usr/include
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$ pkg-config --libs gtest
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-L/home/MYUSER/sysroot/usr/lib64 -lgtest -lpthread
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```
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which contains the correct sysroot now. For a more comprehensive guide to also
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including `${CHOST}` in build system calls, see the excellent tutorial by Diego
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Elio Pettenò: <https://autotools.io/pkgconfig/cross-compiling.html>
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