Dashmips index out of bounds error with Step Over command

[noah978]

Environment:

Python v3.9.0
dashmips v0.1.10 (latest)
dashmips-debugger v0.1.14 (latest)

Explanation

Hello! Thanks for creating this neat extension to use for Assembly debugging. I'm not certain if this should be considered a bug with dashmips or with this Visual Studio Code extension. Essentially, the issue appears to be that when I set a breakpoint as the last line of assembly code and then give the "Step Over" command, the following index out of bounds error occurs. I'm not sure what exactly you are sending to dashmips when the step over command is sent, but it would appear that dashmips runs out of commands in the array of stored commands.

If I hit "continue" instead of "step over", the program does not error out and instead says:

2021-09-13 15:33:05,532 INFO    Recv `{'method': 'continue', 'params': [{'id': 0, 'path': 'd:\\Documents\\Assembly-MIPS\\Hello-World.asm', 'line': 18}]}`
Program counter invalid on (dropped off bottom)

I think the solution on your end is to check what line you are currently debugging, and if it's the last line, change the way you handle the final continue / step over command. If its not something you have the capacity to fix, I can bring up this issue with the dashmips repo instead.

Code

.data
msg: .asciiz "\nHello, World!\n"

.text

main:
    li $v0, 4 # $v0 = 4
    la $a0, msg # $a0 = msg
    syscall

    addi $t0, $zero, 12
    addi $t1, $zero, 7
    add $s0, $t0, $t1
    sub $s1, $t0, $t1

    addi $s2, $zero, 0x10010000
    sw $s0, 0($s2)
    sw $s1, 4($s2)

Images

Log

PS D:\Documents\Assembly-MIPS>  & 'python' '-m' 'dashmips' 'debug' '-i' 'localhost' '-p' '2390' '-l' 'd:\Documents\Assembly-MIPS\Hello-World.asm' 
2021-09-13 15:21:02,835 INFO    Serving on: tcp://localhost:2390
2021-09-13 15:21:02,935 INFO    127.0.0.1 wrote: {'method': 'verify_breakpoints', 'params': [{'id': 0, 'path': 'd:\\Documents\\Assembly-MIPS\\Hello-World.asm', 
'line': 18}]}
2021-09-13 15:21:02,936 INFO    Recv `{'method': 'verify_breakpoints', 'params': [{'id': 0, 'path': 'd:\\Documents\\Assembly-MIPS\\Hello-World.asm', 'line': 18}]}`
2021-09-13 15:21:02,936 INFO    Send `{"method": "verify_breakpoints", "result": [[{"id": 0, "path": "d:\\Documents\\Assembly-MIPS\\Hello-World.asm", "line": 18}], [9]]}`
2021-09-13 15:21:02,937 INFO    127.0.0.1 wrote: {'method': 'start', 'params': []}
2021-09-13 15:21:02,938 INFO    Recv `{'method': 'start', 'params': []}`
2021-09-13 15:21:02,938 INFO    Send `{"method": "start", "result": {"pid": 6576}}`
2021-09-13 15:21:02,938 INFO    127.0.0.1 wrote: {'method': 'continue', 'params': [{'id': 0, 'path': 'd:\\Documents\\Assembly-MIPS\\Hello-World.asm', 'line': 18}]}
2021-09-13 15:21:02,939 INFO    Recv `{'method': 'continue', 'params': [{'id': 0, 'path': 'd:\\Documents\\Assembly-MIPS\\Hello-World.asm', 'line': 18}]}`       

Hello, World!
2021-09-13 15:21:02,946 INFO    Send `{"method": "continue", "result": {"stopped": true, "line": {"filename": "d:\\Documents\\Assembly-MIPS\\Hello-World.asm", "lineno": 18, "line": "sw $s1, 4($s2)"}}}`
2021-09-13 15:21:02,947 INFO    127.0.0.1 wrote: {'method': 'update_visualizer', 'params': ['']}
2021-09-13 15:21:02,948 INFO    Recv `{'method': 'update_visualizer', 'params': ['']}`
2021-09-13 15:21:02,948 INFO    Send `{"method": "update_visualizer", "result": "&&&& &&&& &&&& &&&& &&&& &&&& &&&& &&&& &&&& "}`
2021-09-13 15:21:02,961 INFO    127.0.0.1 wrote: {'method': 'info', 'params': []}
2021-09-13 15:21:02,961 INFO    Recv `{'method': 'info', 'params': []}`
2021-09-13 15:21:02,972 INFO    Send info response
2021-09-13 15:21:03,414 INFO    127.0.0.1 wrote: {'method': 'info', 'params': []}
2021-09-13 15:21:03,414 INFO    Recv `{'method': 'info', 'params': []}`
2021-09-13 15:21:03,424 INFO    Send info response
2021-09-13 15:21:15,171 INFO    127.0.0.1 wrote: {'method': 'step', 'params': []}
2021-09-13 15:21:15,172 INFO    Recv `{'method': 'step', 'params': []}`
----------------------------------------
Exception occurred during processing of request from ('127.0.0.1', 56807)
Traceback (most recent call last):
  File "C:\Program Files\Python39\lib\socketserver.py", line 316, in _handle_request_noblock
    self.process_request(request, client_address)
  File "C:\Program Files\Python39\lib\socketserver.py", line 347, in process_request
    self.finish_request(request, client_address)
  File "C:\Program Files\Python39\lib\socketserver.py", line 360, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "C:\Program Files\Python39\lib\socketserver.py", line 720, in __init__
    self.handle()
  File "C:\Users\noahk\AppData\Roaming\Python\Python39\site-packages\dashmips\debuggerserver.py", line 132, in handle
    response = run_method(command, self.commands)
  File "C:\Users\noahk\AppData\Roaming\Python\Python39\site-packages\dashmips\debuggerserver.py", line 81, in run_method
    result = command(params=params)
  File "C:\Users\noahk\AppData\Roaming\Python\Python39\site-packages\dashmips\debugger.py", line 37, in debug_step
    return {"stopped": True, "line": asdict(program.current_line)}
  File "C:\Users\noahk\AppData\Roaming\Python\Python39\site-packages\dashmips\models.py", line 69, in current_line
    return self.source[pc]
IndexError: list index out of range
----------------------------------------

[nbbeeken]

The debugger's handling could be improved here but the error is caused by not exiting the program correctly, at least in our simulator, you must run syscall instruction with $v0 set to 10 at the end of your main function. That is what the "dropped off bottom" is referring to, as in dropped off bottom of the .text section.

[noah978]

Yes, it’s definitely not correct Assembly code. I was just messing around and figured that the way the error was handled with the continue was much better than the way the step over handled it.