Re: [PATCH] Add an Objfile.lookup_global_symbol function

[Simon Marchi <simark at simark dot ca>]

Hi Christian,

What did you end up deciding, to let Python code search for static symbols?

I just have a few nits on the patch below (and some questions about the doc,
which is why I added Eli in CC).

On 2019-07-22 4:51 p.m., Christian Biesinger via gdb-patches wrote:
> Per the discussion in the thread about my gdb.lookup_global_symbol
> patch, I've changed this patch to only look in GLOBAL_SCOPE.
> 
> This is essentially the inverse of Symbol.objfile. This allows
> handling different symbols with the same name (but from different
> objfiles) and can also be faster if the objfile is known.
> 
> gdb/ChangeLog:
> 
> 2019-06-25  Christian Biesinger  <cbiesinger@google.com>
> 
> 	* NEWS: Mention new function Objfile.lookup_global_symbol.
> 	* python/py-objfile.c (objfpy_lookup_global_symbol): New function
> 	  Objfile.lookup_global_symbol.
> 
> gdb/doc/ChangeLog:
> 
> 2019-06-25  Christian Biesinger  <cbiesinger@google.com>
> 
> 	* python.texi (Objfiles In Python): Document new function
> 	  Objfile.lookup_global_symbol.
> 
> gdb/testsuite/ChangeLog:
> 
> 2019-06-25  Christian Biesinger  <cbiesinger@google.com>
> 
> 	* gdb.python/py-objfile.c: Add global and static vars.
> 	* gdb.python/py-objfile.exp: Test new function Objfile.
> 	  lookup_global_symbol.
> ---
>  gdb/NEWS                                |  3 ++
>  gdb/doc/python.texi                     | 12 ++++++++
>  gdb/python/py-objfile.c                 | 40 ++++++++++++++++++++++++-
>  gdb/testsuite/gdb.python/py-objfile.c   |  3 ++
>  gdb/testsuite/gdb.python/py-objfile.exp |  7 +++++
>  5 files changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/NEWS b/gdb/NEWS
> index cc1d58520d..c57cb4576e 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -36,6 +36,9 @@
>    ** gdb.Type has a new property 'objfile' which returns the objfile the
>       type was defined in.
>  
> +  ** gdb.Objfile has a new method 'lookup_global_symbol' to lookup a symbol
> +     from this objfile only.
> +
>  * New commands
>  
>  | [COMMAND] | SHELL_COMMAND
> diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
> index 034623513b..80da607824 100644
> --- a/gdb/doc/python.texi
> +++ b/gdb/doc/python.texi
> @@ -4441,6 +4441,18 @@ searches then this function can be used to add a debug info file
>  from a different place.
>  @end defun
>  
> +@defun Objfile.lookup_global_symbol (name @r{[}, domain@r{]})
> +Searches for a global symbol named @var{name} in this objfile.  Optionally, the
> +search scope can be restricted with the @var{domain} argument.
> +The @var{domain} argument must be a domain constant defined in the @code{gdb}
> +module and described in @ref{Symbols In Python}.  This function is similar to
> +@code{gdb.lookup_global_symbol}, except that the search is limited to this
> +objfile.
> +
> +The result is a @code{gdb.Symbol} object or @code{None} if the symbol
> +is not found.
> +@end defun
> +
>  @node Frames In Python
>  @subsubsection Accessing inferior stack frames from Python
>  
> diff --git a/gdb/python/py-objfile.c b/gdb/python/py-objfile.c
> index 199c567a04..a9a6ae6725 100644
> --- a/gdb/python/py-objfile.c
> +++ b/gdb/python/py-objfile.c
> @@ -406,7 +406,7 @@ objfpy_is_valid (PyObject *self, PyObject *args)
>    Py_RETURN_TRUE;
>  }
>  
> -/* Implementation of gdb.Objfile.add_separate_debug_file (self) -> Boolean.  */
> +/* Implementation of gdb.Objfile.add_separate_debug_file (self, string) -> None.  */

This appears to be an unrelated (but valid) change.  Can you please make a separate patch
and push it as obvious?  Just mind the 80 columns.  If the function returns None, I think
we could just omit the return type and say:

/* Implementation of gdb.Objfile.add_separate_debug_file (self, string).  */

... and it will fit.

So just push a patch with this (including the ChangeLog entry), and post it to the list
with the "PATCH obvious" prefix, or something like that, to let people know.

>  static PyObject *
>  objfpy_add_separate_debug_file (PyObject *self, PyObject *args, PyObject *kw)
> @@ -434,6 +434,39 @@ objfpy_add_separate_debug_file (PyObject *self, PyObject *args, PyObject *kw)
>    Py_RETURN_NONE;
>  }
>  
> +/* Implementation of gdb.Objfile.lookup_global_symbol (self, string [, domain]) -> gdb.Symbol.  */

> +
> +static PyObject *
> +objfpy_lookup_global_symbol (PyObject *self, PyObject *args, PyObject *kw)
> +{
> +  static const char *keywords[] = { "name", "domain", NULL };
> +  objfile_object *obj = (objfile_object *) self;
> +  const char *symbol_name;
> +  int domain = VAR_DOMAIN;
> +
> +  OBJFPY_REQUIRE_VALID (obj);
> +
> +  if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &symbol_name,
> +					&domain))
> +    return nullptr;
> +
> +  try
> +    {
> +      struct symbol *sym = lookup_global_symbol_from_objfile
> +        (obj->objfile, symbol_name, (domain_enum) domain).symbol;
> +      if (sym == nullptr)
> +	Py_RETURN_NONE;
> +
> +      return symbol_to_symbol_object (sym);
> +    }
> +  catch (const gdb_exception &except)
> +    {
> +      GDB_PY_HANDLE_EXCEPTION (except);
> +    }
> +
> +  Py_RETURN_NONE;
> +}
> +
>  /* Implement repr() for gdb.Objfile.  */
>  
>  static PyObject *
> @@ -652,6 +685,11 @@ Return true if this object file is valid, false if not." },
>      "add_separate_debug_file (file_name).\n\
>  Add FILE_NAME to the list of files containing debug info for the objfile." },
>  
> +  { "lookup_global_symbol", (PyCFunction) objfpy_lookup_global_symbol,
> +    METH_VARARGS | METH_KEYWORDS,
> +    "lookup_global_symbol (name [, domain]).\n\
> +Looks up a global symbol in this objfile and returns it." },
> +

To be consistent with the rest of the Python function help strings, I think it should
be

  "Look up a global symbol in this objfile and return it."

i.e. not at the third person of the singular.  Eli, could you tell which form is preferred?
The change to python.texi might also need to be changed to that form as well.

>    { NULL }
>  };
>  
> diff --git a/gdb/testsuite/gdb.python/py-objfile.c b/gdb/testsuite/gdb.python/py-objfile.c
> index ac41491234..6d751bddae 100644
> --- a/gdb/testsuite/gdb.python/py-objfile.c
> +++ b/gdb/testsuite/gdb.python/py-objfile.c
> @@ -15,6 +15,9 @@
>     You should have received a copy of the GNU General Public License
>     along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
>  
> +int global_var = 42;
> +static int static_var = 50;
> +
>  int
>  main ()
>  {
> diff --git a/gdb/testsuite/gdb.python/py-objfile.exp b/gdb/testsuite/gdb.python/py-objfile.exp
> index b5e0c5e760..2e8358bd76 100644
> --- a/gdb/testsuite/gdb.python/py-objfile.exp
> +++ b/gdb/testsuite/gdb.python/py-objfile.exp
> @@ -55,6 +55,13 @@ gdb_test "python print (gdb.lookup_objfile (\"${testfile}\").filename)" \
>  gdb_test "python print (gdb.lookup_objfile (\"junk\"))" \
>      "Objfile not found\\.\r\n${python_error_text}"
>  
> +gdb_test "python print (gdb.lookup_objfile (\"${testfile}\").lookup_global_symbol (\"global_var\").name)" \
> +    "global_var" "lookup_global_symbol finds a valid symbol"
> +gdb_test "python print gdb.lookup_objfile (\"${testfile}\").lookup_global_symbol (\"static_var\") is None" \
> +    "True" "lookup_global_symbol does not find static symbols"

Please add parentheses to this print so it works with Python 3.

> +gdb_test "python print (gdb.lookup_objfile (\"${testfile}\").lookup_global_symbol (\"stdout\"))" \
> +    "None" "lookup_global_symbol doesn't find symbol in other objfile"
> +
>  set binfile_build_id [get_build_id $binfile]
>  if [string compare $binfile_build_id ""] {
>      verbose -log "binfile_build_id = $binfile_build_id"
> 

Simon