I use CMake with GNU Make and would like to see all commands exactly (for example how the compiler is executed, all the flags etc.).
GNU make has --debug, but it does not seem to be that helpful are there any other options? Does CMake provide additional flags in the generated Makefile for debugging purpose?
mkdir build; cd build; cmake .. --debug-output; make VERBOSE=1
When you run make, add VERBOSE=1 to see the full command output. For example:
cmake .
make VERBOSE=1
Or you can add -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON to the cmake command for permanent verbose command output from the generated Makefiles.
cmake -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON .
make
To reduce some possibly less-interesting output you might like to use the following options. The option CMAKE_RULE_MESSAGES=OFF removes lines like [ 33%] Building C object..., while --no-print-directory tells make to not print out the current directory filtering out lines like make[1]: Entering directory and make[1]: Leaving directory.
cmake -DCMAKE_RULE_MESSAGES:BOOL=OFF -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON .
make --no-print-directory
It is convenient to set the option in the CMakeLists.txt file as:
set(CMAKE_VERBOSE_MAKEFILE ON)
CMAKE_VERBOSE_MAKEFILE should be off by default and a user's choice, if they need it, for debugging purposes.
Or simply export VERBOSE environment variable on the shell like this: export VERBOSE=1
VERBOSE to 1 works both for MSVC & MinGW. If you want to undo this, you need to set it to empty, not 0.
If you use the CMake GUI then swap to the advanced view and then the option is called CMAKE_VERBOSE_MAKEFILE.
I was trying something similar to ensure the -ggdb flag was present.
Call make in a clean directory and grep the flag you are looking for. Looking for debug rather than ggdb I would just write.
make VERBOSE=1 | grep debug
The -ggdb flag was obscure enough that only the compile commands popped up.
cmake --build . --verbose
On Linux and with Makefile generation, this is likely just calling make VERBOSE=1 under the hood, but cmake --build can be more portable for your build system, e.g. working across OSes or if you decide to do e.g. Ninja builds later on:
mkdir build
cd build
cmake ..
cmake --build . --verbose
Its documentation also suggests that it is equivalent to VERBOSE=1:
--verbose, -v Enable verbose output - if supported - including the build commands to be executed. This option can be omitted if VERBOSE environment variable or CMAKE_VERBOSE_MAKEFILE cached variable is set.
Tested on Cmake 3.22.1, Ubuntu 22.04.
cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=TRUE will generate a file with all compilation commands.
This file is required by some LSP to know how to compile a source file out of the box, but it could also help for debugging compilation problems.
The output file is named ${CMAKE_BINARY_DIR}/compile_commands.json.
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cmake -GNinja . ; ninja -vshows a very nice verbose output with minimal fluff.cmake --build . -- VERBOSE=1-DCMAKE_EXPORT_COMPILE_COMMANDS=ONin that case, such that we have all the commands in the filecompile_commands.jsonwithout actually building the sources.