Incorrect Source File Paths

Usage
1

I created a very simple CMake project to demonstrate my issue.

├── CMakeLists.txt
└── apps
    ├── CMakeLists.txt
    └── src
        └── main.cpp

# CMakeLists.txt
cmake_minimum_required(VERSION 3.19)

# Set the project name
project (hello_cmake)

set(CMAKE_BUILD_TYPE Debug)

add_subdirectory(apps)

# apps/CMakeLists.txt
add_executable(main src/main.cpp)

// main.cpp
#include <iostream>

int main(int argc, char *argv[])
{
   std::cout << "Hello CMake!" << std::endl;
   return 0;
}

When I build the project

cmake -S . -B build
cd build/ && make

The source file paths in the executable are weird.

readelf -wi apps/main | grep -B1 DW_AT_comp_dir
    <12>   DW_AT_name        : (indirect line string, offset: 0x22): /home/user/cmaketest/apps/src/main.cpp
    <16>   DW_AT_comp_dir    : (indirect line string, offset: 0x0): /home/user/cmaketest/build/apps

When a debugger looks for source files it will try DW_AT_comp_dir + DW_AT_name which is not a valid path.

2

I closed this other related thread because this has a reproducer:

Based on this GCC thread it seems to be based on whether the source file is passed as an absolute or relative path. CMake tends to generate absolute paths on command lines. I think that the -fdebug-prefix-map= flag is what is wanted here.

Edit:

Yes, adding this:

add_compile_options(-fdebug-prefix-map=${CMAKE_SOURCE_DIR}=SRC)

results in:

% readelf -wi build/apps/main | grep -B1 DW_AT_comp_dir
    <12>   DW_AT_name        : (indirect line string, offset: 0x0): SRC/apps/src/main.cpp
    <16>   DW_AT_comp_dir    : (indirect line string, offset: 0x16): SRC/build/apps
3

Thanks. I changed it to

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fdebug-prefix-map=`pwd`=\ ")

resulting in:

readelf -wi build/apps/main | grep -B1 DW_AT_comp_dir
    <12>   DW_AT_name        : (indirect line string, offset: 0x0): /home/user/cmaketest/apps/src/main.cpp
    <16>   DW_AT_comp_dir    : (indirect line string, offset: 0x7e):

This works. Is this the cleanest way to do it?

4

Maybe? Note that the `pwd` bit is a hack that (I’m pretty sure) won’t work in the Ninja generator. You should probably make explicit entries for various CMake directory variables.