PDI-2024: Symbolic debugging of a program.

Just because a program has no compilation errors does not mean that it works correctly. In case of malfunction, the program must be debugged to find the problem. Symbolic debugging allows to execute the program in a controlled way, step by step, stopping its execution and visualizing the value of the variables as we go along the program flow.

It is recommended to review the concepts of breakpoint, step-over, step-into and continue, in addition to the debugging procedures described in https://hackmd.io/@parraman/prog-lab-gfie-practica-0#Depurando-programas.

Debug Configurations

In order to be able to debug symbolically, it is necessary to define a debug configuration in eclipse. This is done through the Run -> Debug Configurations option.

In the previous image you can see the DEBUG_P0 configuration created in the GDB Hardware Debugging section and that refers to the P0 project. Using the options above the configuration explorer on the left it is possible to manage new configurations or delete the ones that are no longer used.

The main tab simply contains the name of the P0 project and the Debug/P0 binary to be debugged. If you want to debug another program, the corresponding configuration should be created by changing the name of the project.

The Debugger tab contains the debugger to be used, in this case riscv-gaisler-elf-gdb. This debugger will connect to the SPIKE simulator via a socket connection, on port 3333 and both are on the same localhost computer.

debugP0 script

Ensure that the ./debugP0 script contains the following commands:

gnome-terminal -- picsimlab
sleep 1 
gnome-terminal -- spike -H --isa=RV32IM --rbb-port=9824 -m0x40000000:0x100000,0xFFFF0000:0x10000 ./Debug/P0
gnome-terminal -- openocd -f spike.cfg

Debugging the example program

Before debugging, it is necessary to compile and generate the corresponding binary.

Once the binary has been generated, type ./debugP0 in the terminal window opened in the previous section.

Like ./runP0, ./debugP0 is a script whose contents can be viewed and edited. In subsequent practices we will modify this script to adapt it to the new practice projects.

When executing this script four new command windows will be opened. Two corresponds to the SPIKE simulator in debug mode and that waits for the program to be sent from eclipse, in this window the messages that are printed from the code will be shown.

Listening for remote bitbang connection on port 9824.

The other window corresponds to a program called openocd which acts as a bridge between SPIKE and eclipse. We will not have to interact with it.

Next we proceed to launch the debug configuration DEBUG_P0. Make sure that the selected configuration is

and click the icon

.

The following image shows the debugging perspective. By default a breakpoint is active at the beginning of the main function.

At this point the debugger waits for user commands to advance the execution of the program. The main commands for debugging are:

1. Enable/disable breakpoints: Toggle Breakpoint
2. Continue execution: Continue
3. Execute a function completely: Step Over
4. Enter to debug a function: Step into

All these commands are available through the Run menu but are also accessible through the

icons. Review the debugging concepts in https://hackmd.io/@parraman/prog-lab-gfie-practica-0#Depurando-programas.

Run the program completely and return to the compilation perspective.

If you press Continue at this point, the program will run completely, the debugger windows will close and you will not see the message printed on the screen.

To return to the compilation perspective of the program click

in the upper right corner. This option is also available in the menu Window –> Perspective –> Open Perspective –> C/C++.

Duplicate Debug configuration and modify it to debug another project

By using mouse right button over DEBUG_P0 is posible to make a copy of the debug configuration. After that, rename it and change all project names to the new one.