Make gcc put relative filenames in debug information

You can use the -fdebug-prefix-map flag to remap the debugging information paths. For example, to make the paths relative to the build location use: -fdebug-prefix-map=/full/build/path=.

You can set the RULE_LAUNCH_COMPILE property of a CMake target to have CMake invoke a shell script which transforms the source file path to a project relative path before invoking gcc. Use the CMake function configure_file to generate a shell script which knows about the PROJECT_SOURCE_DIR and PROJECT_BINARY_DIR of your project.

In your outermost CMakeLists.txt add the following code:

configure_file(
    "${PROJECT_SOURCE_DIR}/gcc_debug_fix.sh.in"
    "${PROJECT_BINARY_DIR}/gcc_debug_fix.sh"
    @ONLY)

add_executable (MyExecutable ...)

set_target_properties(MyExecutable PROPERTIES 
    RULE_LAUNCH_COMPILE "${PROJECT_BINARY_DIR}/gcc_debug_fix.sh")

The following template shell script gcc_debug_fix.sh.in needs to go to the root directory of the CMake project:

#!/bin/sh

PROJECT_BINARY_DIR="@PROJECT_BINARY_DIR@"
PROJECT_SOURCE_DIR="@PROJECT_SOURCE_DIR@"

# shell script invoked with the following arguments
# $(CXX) $(CXX_DEFINES) $(CXX_FLAGS) -o OBJECT_FILE -c SOURCE_FILE

# extract parameters
SOURCE_FILE="${@: -1:1}"
OBJECT_FILE="${@: -3:1}"
COMPILER_AND_FLAGS=${@:1:$#-4}

# make source file path relative to project source dir
SOURCE_FILE_RELATIVE="${SOURCE_FILE:${#PROJECT_SOURCE_DIR} + 1}"

# make object file path absolute
OBJECT_FILE_ABSOLUTE="$PROJECT_BINARY_DIR/$OBJECT_FILE"

cd "$PROJECT_SOURCE_DIR"

# invoke compiler
exec $COMPILER_AND_FLAGS -c "${SOURCE_FILE_RELATIVE}" -o "${OBJECT_FILE_ABSOLUTE}"

The shell script uses the information from the variables PROJECT_BINARY_DIR and PROJECT_SOURCE_DIR to transform the path of the source file to a path relative to the project root and the object file's path to an absolute path. Because gcc gets passed a project relative path now, .debug_str should use that path, too.

The following caveats apply:

• Be sure to set the executable bit of gcc_debug_fix.sh.in.
• For the script to work CMAKE_USE_RELATIVE_PATHS has to set to OFF again.
• The script makes assumptions about the location of the file paths on the command line. This may not work if CMake uses a different rule to invoke the compiler. A more robust solution would be to scan the script arguments for the -o and -c flags.