On 4/11/24 18:07, Tom Tromey wrote:
>>>>>> "Tom" == Tom de Vries <tdevries@suse.de> writes:
> 
> Tom> PR python/31631 reports a gdb internal error when doing:
> Tom> ...
> Tom> (gdb) python gdb.selected_inferior().read_memory (0, 0xffffffffffffffff)
> Tom> utils.c:709: internal-error: virtual memory exhausted.
> Tom> A problem internal to GDB has been detected,
> Tom> further debugging may prove unreliable.
> Tom> ...
> 
> Tom> Fix this by throwing a python MemoryError, such that we have instead:
> Tom> ...
> Tom> (gdb) python gdb.selected_inferior().read_memory (0, 0xffffffffffffffff)
> Tom> Python Exception <class 'MemoryError'>:
> Tom> Error occurred in Python.
> Tom> (gdb)
> Tom> ...
> 
> I tend to think you will regret opening this door, because I imagine
> there are a large number of ways to crash gdb by passing nonsensical
> values to Python APIs.
> 

Hm, ok then let's hope I don't regret it.

> Tom>  @request("readMemory")
> Tom>  @capability("supportsReadMemoryRequest")
> Tom>  def read_memory(*, memoryReference: str, offset: int = 0, count: int, **extra):
> Tom>      addr = int(memoryReference, 0) + offset
> Tom> -    buf = gdb.selected_inferior().read_memory(addr, count)
> Tom> +    oom = False
> Tom> +    try:
> Tom> +        buf = gdb.selected_inferior().read_memory(addr, count)
> Tom> +    except MemoryError:
> Tom> +        oom = True
> Tom> +    if oom:
> Tom> +        raise DAPException("Out of memory")
> 
> This should probably chain the memory error in the except block and
> re-throw.  See https://peps.python.org/pep-3134/
> 

Ack, that's what I had initially, but I ran into an error that I can no 
longer reproduce ... so, I'm not sure what happened there.  Anyway, fixed.

> However I don't really understand why this is needed.  Isn't the
> exception already propagated back to the server thread?
> 

Without it I run into:
...
FAIL: gdb.dap/memory.exp: exceptions in log file
...
because in the dap log we have:
...
READ: <<<{"seq": 7, "type": "request", "command": "readMemory", 
"arguments": {"memoryReference": "0x402010", "count": 
18446744073709551615}}>>>
Traceback (most recent call last):
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/server.py", 
line 157, in _handle_command
     body = _commands[params["command"]](**args)
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/server.py", 
line 300, in check
     return func(*args, **kwargs)
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/server.py", 
line 360, in sync_call
     return send_gdb_with_response(lambda: func(**args))
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/server.py", 
line 514, in send_gdb_with_response
     raise val
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/server.py", 
line 470, in __call__
     val = self.fn()
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/server.py", 
line 360, in <lambda>
     return send_gdb_with_response(lambda: func(**args))
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/startup.py", 
line 113, in ensure_gdb_thread
     return func(*args, **kwargs)
   File 
"/data/vries/gdb/leap-15-5/build/gdb/data-directory/python/gdb/dap/memory.py", 
line 28, in read_memory
     buf = gdb.selected_inferior().read_memory(addr, count)
MemoryError
WROTE: <<<{"request_seq": 7, "type": "response", "command": 
"readMemory", "success": false, "message": ""}>>>
...

So that needs fixing here:
...
diff --git a/gdb/python/lib/gdb/dap/server.py 
b/gdb/python/lib/gdb/dap/server.py
index 7eb87177710..8408232eceb 100644
--- a/gdb/python/lib/gdb/dap/server.py
+++ b/gdb/python/lib/gdb/dap/server.py
@@ -173,6 +173,9 @@ class Server:
              log_stack(LogLevel.FULL)
              result["success"] = False
              result["message"] = str(e)
+        except MemoryError as e:
+            result["success"] = False
+            result["message"] = str(e)
          except BaseException as e:
...

But I couldn't come up with a good rationale as to why I should handle 
MemoryError differently from BaseException, so I decided to catch it 
locally and turn it into a DAPException.

> Tom> +      /* We used to use xmalloc, which does this trick to avoid malloc
> Tom> +	 returning a nullptr for a valid reason.  Keep doing the same.  */
> Tom> +      if (length == 0)
> Tom> +	length = 1;
> 
> This is most likely a workaround for vendor implementations of malloc
> that return NULL for malloc(0).  See
> https://www.gnu.org/software/gnulib/manual/html_node/malloc.html
> 
> However, here this is not necessary, because a 0-length memory read is
> meaningless, and so this case can simply be reported as an error.

I went for backward compatibility here, but ok, fixed.  Updated version 
attached.

Thanks,
- Tom