Use GDB to trace two variables and check if the offset/pointer value has grown beyond the end value

gdb_script.py

# Trace two variables and check if the offset/pointer value has grown beyond the end
# We assume/know that rl_point > rl_end is true as we use reverse debugging with rr
# We want to find the point were everything was okay.
# enter "interactive" python shell with 'pi' and exit after pasting with 'ctrl+d'

POINT_VAR_NAME = 'rl_point'
END_VAR_NAME = 'rl_end'

class bcolors:
    FAIL = '\033[91m'
    ENDC = '\033[0m'
    BOLD = '\033[1m'
    UNDERLINE = '\033[4m'

class CompareBreakpoint(gdb.Breakpoint):
    def stop(self):
        point_value = gdb.lookup_symbol(POINT_VAR_NAME)[0].value()
        end_value = gdb.lookup_symbol(END_VAR_NAME)[0].value()
        #if a difference of e.g. 1 is accetable
        #if (end_value - point_value) < -1:
        if point_value <= end_value:
            print(f'{bcolors.FAIL} {bcolors.BOLD} {bcolors.UNDERLINE}')
            print(f'[!] {END_VAR_NAME}: {end_value} \t {POINT_VAR_NAME}: {point_value}')
            print(f'{bcolors.ENDC}', end='')
            return True
        return False

CompareBreakpoint(END_VAR_NAME, gdb.BP_WATCHPOINT, gdb.WP_WRITE)
CompareBreakpoint(POINT_VAR_NAME, gdb.BP_WATCHPOINT, gdb.WP_WRITE)