Re: [PING][RFC][PATCH v2] Python API: add gdb.stack_may_be_invalid

[Martin Galvan <martin.galvan@tallertechnologies.com>]

On Wed, Nov 12, 2014 at 2:06 PM, Doug Evans <dje@google.com> wrote:
> Broken patch.  Cut-n-paste error or unhelpful mail program?

Probably the second one. Will fix it for the next version.

>> +   and -1 if we have no debug info to use. */
>> +
>> +static int
>> +pc_may_be_in_prologue (gdb_py_ulongest pc)
>> +{
>> +  int result = -1;
>> +  struct symbol *function_symbol;
>> +  struct symtab_and_line function_body_start_sal;
>> +
>> +  function_symbol = find_pc_function(pc);
>> +
>> +  if (function_symbol)
>
> gdb's coding style convention is to write function_symbol != NULL.

Indeed, I must've missed that one!

>> +    {
>> +      function_body_start_sal = find_function_start_sal (function_symbol, 1);
>> +
>> +      result = pc < function_body_start_sal.pc;
>
> IWBN if the higher level API provided a routine rather than the python
> code having to hand-code this test.  IOW, "pc_may_be_in_prologue"
> should live in gdb/*.c, not gdb/python/*.c.
> [As for which file, in gdb/*.c, symtab.c would be fine for now I think.]
>> +    }
>> +
>> +    return result;
>> +}
>> +
>
> Missing function comment for stack_is_destroyed.
> As a rule they all must have them.

Will do.

> Plus the name "stack is destroyed" is confusing.
> This function is just a wrapper around gdbarch_in_function_epilogue_p
> so I'd just call it in_function_epilogue_p (or
> gdbpy_in_function_epilogue_p or some such).

In the last thread (
https://www.sourceware.org/ml/gdb-patches/2014-10/msg00590.html ) we
discussed that and Pedro pointed out that
gdbarch_in_function_epilogue_p itself is misnamed, and we shouldn't
carry that confusion to the Python API.

>> +static int
>> +stack_is_destroyed (gdb_py_ulongest pc)
>> +{
>> +  int result;
>> +  struct symtab *symtab = NULL;
>> +  struct gdbarch *gdbarch = NULL;
>> +
>> +  symtab = find_pc_symtab (pc);
>> +
>> +  if ((symtab != NULL) && (symtab->objfile != NULL))
>> +    {
>> +      gdbarch = get_objfile_arch (symtab->objfile);
>> +    }
>
> Convention is to not use braces when the code occupies one line.

As you wish.

>> +
>> +  if (gdbarch != NULL)
>> +    {
>> +      result = gdbarch_in_function_epilogue_p (gdbarch, pc);
>> +    }
>> +  else
>> +    {
>> +      result = gdbarch_in_function_epilogue_p (python_gdbarch, pc);
>> +    }
>
> This code would be simpler if written as:
>
>    if (gdbarch == NULL)
>      gdbarch = python_gdbarch;
>
>   result = gdbarch_function_in_epilogue_p (python_gdbarch);
>> +
>> +  return result;
>> +}
>> +
>> +/* Returns True if a given PC may point to an address in which the stack frame
>> +   may not be valid (either because it may not be set up yet or because it was
>> +   destroyed, usually in a function's epilogue), False otherwise. */
>> +
>> +static PyObject *
>> +gdbpy_stack_may_be_invalid (PyObject *self, PyObject *args)
>> +{
>> +  gdb_py_ulongest pc;
>> +  PyObject *result = NULL;
>> +  int pc_maybe_in_prologue;
>> +
>> +  if (PyArg_ParseTuple (args, GDB_PY_LLU_ARG, &pc))
>> +    {
>> +      pc_maybe_in_prologue = pc_may_be_in_prologue (pc);
>> +
>> +      if (pc_maybe_in_prologue != -1)
>> +        {
>> +          result = stack_is_destroyed (pc) || pc_maybe_in_prologue ?
>
> It'd be more efficient to avoid an unnecessary call to
> stack_is_destroyed by checking pc_maybe_in_prologue first.
>> +                   Py_True : Py_False;
>> +
>> +          Py_INCREF (result);
>> +        }
>> +      else  /* No debug info at that point. */
>> +        {
>> +          PyErr_Format (PyExc_RuntimeError,
>> +                        _("There's no debug info for a function that\n"
>> +                          "could be enclosing the given PC."));
>
> A newline in an error message feels odd.
> I'd remove it.
>> +        }
>> +    }
>> +
>> +  return result;
>> +}
>> +
>>  /* A Python function which is a wrapper for decode_line_1.  */
>>
>>  static PyObject *
>> @@ -2000,6 +2081,15 @@ Return the selected inferior object." },
>>    { "inferiors", gdbpy_inferiors, METH_NOARGS,
>>      "inferiors () -> (gdb.Inferior, ...).\n\
>>  Return a tuple containing all inferiors." },
>> +
>> +
>> +  { "stack_may_be_invalid", gdbpy_stack_may_be_invalid, METH_VARARGS,
>> +    "stack_may_be_invalid (Long) -> Boolean.\n\
>> +Returns True if a given PC may point to an address in which the stack frame\n\
>> +may not be valid (either because it may not be set up yet or because it was\n\
>> +destroyed, usually in a function's epilogue), False otherwise."},
>
> The name "stack_may_be_invalid" is confusing.
> It's not that the stack is invalid, rather that locals in the stack
> frame are inaccessible.
> stack_frame_may_be_invalid?

Indeed, will fix those as well. Thanks a lot for the feedback!

-- 

Martín Galván

Software Engineer

Taller Technologies Argentina

San Lorenzo 47, 3rd Floor, Office 5

Córdoba, Argentina

Phone: 54 351 4217888 / +54 351 4218211