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LAB 05: GDB Debugging & Breakpoint Analysis | Debugging Techniques & Code Execution
QUIZ gdb basics and phase03.c
=============================
Starting Up
~~~~~~~~~~~
After starting up GDB with the 'phase03' program, the 'run' command
will yield output like the following:
,----
| > gdb ./phase03
| ...
|
| (gdb) run
| Starting program: ./phase03
| usage: ./phase03 <infile>
| [Inferior 1 (process 44495) exited with code 01]
`----
which means that the 'phase03' program wants a command line
argument. How does one accomplish this in GDB?
- ( ) Use the command 'set args input.txt' once and then each 'run'
will use those arguments
- ( ) Use the command 'run input.txt' each time you run
- (X) Either of the above will work
- ( ) Start GDB as 'gdb ./phase03 input.txt'
Setting a Breakpoint
~~~~~~~~~~~~~~~~~~~~
Which of the following commands will set a breakpoint in GDB at the
line that reads 'int hit = shot ^ targ;'?
- ( ) 'break int hit = shot ^ targ'
- ( ) 'break phase03'
- (X) 'break phase03.c:37'
- ( ) 'break next hit'
After hitting the specified breakpoint, which of the following GDB
commands will advance to where the next **breakpoint** that is set?
- ( ) 'next'
- (X) 'continue'
- ( ) 'run'
- ( ) 'advance'
next command in gdb
~~~~~~~~~~~~~~~~~~~
During a debugging session, the debugger has 'phase03' stopped at the line
indicated below via a '>' character.
,----
| /// INITIAL ///
| void phase02() {
| int a = atoi(next_input());
| > int b = atoi(next_input());
| int c = atoi(next_input());
| ....
|
| char *next_input() {
| input_idx++;
| int ret = fscanf(input_fh, "%s", inputs[input_idx]);
| ...
|
`----
When the 'next' command is executed by GDB, then the debugger executes
some code and leaves the state of the running program in one of the
following positions:
,----
| /// OPTION A ///
| void phase02() {
| int a = atoi(next_input());
| int b = atoi(next_input());
| > int c = atoi(next_input());
| ....
|
| char *next_input() {
| input_idx++;
| int ret = fscanf(input_fh, "%s", inputs[input_idx]);
| ...
|
| /// OPTION B ///
| void phase02() {
| int a = atoi(next_input());
| > int b = atoi(next_input());
| int c = atoi(next_input());
| ....
|
| char *next_input() {
| input_idx++;
| int ret = fscanf(input_fh, "%s", inputs[input_idx]);
| ...
|
| /// OPTION C ///
| void phase02() {
| int a = atoi(next_input());
| int b = atoi(next_input());
| int c = atoi(next_input());
| ....
|
| char *next_input() {
| > input_idx++;
| int ret = fscanf(input_fh, "%s", inputs[input_idx]);
| ...
`----
After executing 'next', which option correctly indicates where GDB
will get control back?
- (X) OPTION A because 'next' moves to the next line of code executing
all functions and operations on a given line.
- ( ) OPTION B because 'next' executes the next operation and
completes it which will be the 'next_input()' function but the
'atoi()' function will not be run
- ( ) OPTION C because 'next' steps into functions and executes the
next operation which is to start running the 'next_input()'
function.
step command in gdb
~~~~~~~~~~~~~~~~~~~
Instead of using the 'next' command in the above example, what if the
'step' command was used instead from the 'INITIAL' position? Which
'OPTION' represents the code position GDB would be at after 'step'?
- ( ) OPTION A because 'step' moves to the next line of code executing
all functions and operations on a given line.
- ( ) OPTION B because 'step' executes the next operation and
completes it which will be the 'next_input()' function but the
'atoi()' function will not be run
- (X) OPTION C because 'step' steps into functions and executes the
next operation which is to start running the 'next_input()'
function.
CODE input.txt for phase03
==========================
The mock 'phase03' program can be compiled via 'make' and run via
,----
| > ./phase03 input.txt
`----
Use 'gdb' and analyze what inputs are required in the file 'input.txt'
in order to "pass" the phase. A correct run yields the output:
,----
| > ./phase03 input.txt
| Running mock Phase03
| Right on target: nice shootin' bitslinger!
| Phase complete
`----
which is checked for in the CODE tests.
Test that the code behaves correctly via the command
,----
| make test-code
`----
and verify that both code/quiz are correct via
,----
| make test
`----
before using
,----
| make zip
`----
to create a zip to submit.