[v4] Make GDB compile with Python 3 on MinGW

  PyFile_FromString and PyFile_AsFile have been removed in Python 3.
There is no obvious replacement that works here, and we can't just
pass our FILE* to a DLL in Windows because it may use a different
C runtime.

So we just call a Python function which reads and executes file
contents. Care must be taken to execute it in the context of
__main__.

Tested by inverting the ifdef and running the testsuite on Debian
Linux (even without the patch, I failed at running the testsuite
on Windows). I did test with both Python 2 and 3.

gdb/ChangeLog:

2019-08-13  Christian Biesinger  <cbiesinger@google.com>

	* python/lib/gdb/__init__.py: Add an execute_file function.
	* python/python.c (python_run_simple_file): Call gdb.execute_file
	on Windows.
---
 gdb/python/lib/gdb/__init__.py | 26 ++++++++++++++++++++++++++
 gdb/python/python.c            | 23 ++++++++++++++---------
 2 files changed, 40 insertions(+), 9 deletions(-)
  

Ping

On Thu, Aug 15, 2019 at 1:49 PM Christian Biesinger
<cbiesinger@google.com> wrote:
>
> PyFile_FromString and PyFile_AsFile have been removed in Python 3.
> There is no obvious replacement that works here, and we can't just
> pass our FILE* to a DLL in Windows because it may use a different
> C runtime.
>
> So we just call a Python function which reads and executes file
> contents. Care must be taken to execute it in the context of
> __main__.
>
> Tested by inverting the ifdef and running the testsuite on Debian
> Linux (even without the patch, I failed at running the testsuite
> on Windows). I did test with both Python 2 and 3.
>
> gdb/ChangeLog:
>
> 2019-08-13  Christian Biesinger  <cbiesinger@google.com>
>
>         * python/lib/gdb/__init__.py: Add an execute_file function.
>         * python/python.c (python_run_simple_file): Call gdb.execute_file
>         on Windows.
> ---
>  gdb/python/lib/gdb/__init__.py | 26 ++++++++++++++++++++++++++
>  gdb/python/python.c            | 23 ++++++++++++++---------
>  2 files changed, 40 insertions(+), 9 deletions(-)
>
> diff --git a/gdb/python/lib/gdb/__init__.py b/gdb/python/lib/gdb/__init__.py
> index af74df80c8..afe5b08f3a 100644
> --- a/gdb/python/lib/gdb/__init__.py
> +++ b/gdb/python/lib/gdb/__init__.py
> @@ -106,6 +106,32 @@ def execute_unwinders(pending_frame):
>
>      return None
>
> +def _execute_file(filepath):
> +    """This function is used to replace Python 2's PyRun_SimpleFile.
> +
> +    Loads and executes the given file.
> +
> +    We could use the runpy module, but its documentation says:
> +    "Furthermore, any functions and classes defined by the executed code are
> +    not guaranteed to work correctly after a runpy function has returned."
> +    """
> +    globals = sys.modules['__main__'].__dict__
> +    set_file = False
> +    # Set file (if not set) so that the imported file can use it (e.g. to
> +    # access file-relative paths). This matches what PyRun_SimpleFile does.
> +    if not hasattr(globals, '__file__'):
> +        globals['__file__'] = filepath
> +        set_file = True
> +    try:
> +        with open(filepath, 'rb') as file:
> +            # We pass globals also as locals to match what Python does
> +            # in PyRun_SimpleFile.
> +            compiled = compile(file.read(), filepath, 'exec')
> +            exec(compiled, globals, globals)
> +    finally:
> +        if set_file:
> +            del globals['__file__']
> +
>
>  # Convenience variable to GDB's python directory
>  PYTHONDIR = os.path.dirname(os.path.dirname(__file__))
> diff --git a/gdb/python/python.c b/gdb/python/python.c
> index 162470dcc0..cca7c4cd6b 100644
> --- a/gdb/python/python.c
> +++ b/gdb/python/python.c
> @@ -323,9 +323,8 @@ python_interactive_command (const char *arg, int from_tty)
>     A FILE * from one runtime does not necessarily operate correctly in
>     the other runtime.
>
> -   To work around this potential issue, we create on Windows hosts the
> -   FILE object using Python routines, thus making sure that it is
> -   compatible with the Python library.  */
> +   To work around this potential issue, we run code in Python to load
> +   the script.  */
>
>  static void
>  python_run_simple_file (FILE *file, const char *filename)
> @@ -339,15 +338,21 @@ python_run_simple_file (FILE *file, const char *filename)
>    /* Because we have a string for a filename, and are using Python to
>       open the file, we need to expand any tilde in the path first.  */
>    gdb::unique_xmalloc_ptr<char> full_path (tilde_expand (filename));
> -  gdbpy_ref<> python_file (PyFile_FromString (full_path.get (), (char *) "r"));
> -  if (python_file == NULL)
> +
> +  if (gdb_python_module == nullptr
> +      || ! PyObject_HasAttrString (gdb_python_module, "_execute_file"))
> +    error (_("Installation error: gdb._execute_file function is missing"));
> +
> +  gdbpy_ref<> return_value
> +    (PyObject_CallMethod (gdb_python_module, "_execute_file", "s",
> +                         full_path.get ()));
> +  if (return_value == nullptr)
>      {
> -      gdbpy_print_stack ();
> -      error (_("Error while opening file: %s"), full_path.get ());
> +      /* Use PyErr_PrintEx instead of gdbpy_print_stack to better match the
> +         behavior of the non-Windows codepath.  */
> +      PyErr_PrintEx(0);
>      }
>
> -  PyRun_SimpleFile (PyFile_AsFile (python_file.get ()), filename);
> -
>  #endif /* _WIN32 */
>  }
>
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>
  

On 2019-08-15 2:49 p.m., Christian Biesinger via gdb-patches wrote:
> PyFile_FromString and PyFile_AsFile have been removed in Python 3.
> There is no obvious replacement that works here, and we can't just
> pass our FILE* to a DLL in Windows because it may use a different
> C runtime.
> 
> So we just call a Python function which reads and executes file
> contents. Care must be taken to execute it in the context of
> __main__.
> 
> Tested by inverting the ifdef and running the testsuite on Debian
> Linux (even without the patch, I failed at running the testsuite
> on Windows). I did test with both Python 2 and 3.
> 
> gdb/ChangeLog:
> 
> 2019-08-13  Christian Biesinger  <cbiesinger@google.com>
> 
> 	* python/lib/gdb/__init__.py: Add an execute_file function.

This can be written as:

  * python/lib/gdb/__init__.py (_execute_file): New function.

> 	* python/python.c (python_run_simple_file): Call gdb.execute_file
> 	on Windows.

Please update "execute_file" to "_execute_file" in both entries.

The patch LGTM with this fixed.

Thanks,

Simon
  

On Thu, Aug 22, 2019 at 5:24 PM Simon Marchi <simark@simark.ca> wrote:
>
> On 2019-08-15 2:49 p.m., Christian Biesinger via gdb-patches wrote:
> > PyFile_FromString and PyFile_AsFile have been removed in Python 3.
> > There is no obvious replacement that works here, and we can't just
> > pass our FILE* to a DLL in Windows because it may use a different
> > C runtime.
> >
> > So we just call a Python function which reads and executes file
> > contents. Care must be taken to execute it in the context of
> > __main__.
> >
> > Tested by inverting the ifdef and running the testsuite on Debian
> > Linux (even without the patch, I failed at running the testsuite
> > on Windows). I did test with both Python 2 and 3.
> >
> > gdb/ChangeLog:
> >
> > 2019-08-13  Christian Biesinger  <cbiesinger@google.com>
> >
> >       * python/lib/gdb/__init__.py: Add an execute_file function.
>
> This can be written as:
>
>   * python/lib/gdb/__init__.py (_execute_file): New function.
>
> >       * python/python.c (python_run_simple_file): Call gdb.execute_file
> >       on Windows.
>
> Please update "execute_file" to "_execute_file" in both entries.
>
> The patch LGTM with this fixed.

Thanks, pushing now with that fixed.


Christian
  

On Thu, Aug 22, 2019 at 6:47 PM Christian Biesinger
<cbiesinger@google.com> wrote:
>
> On Thu, Aug 22, 2019 at 5:24 PM Simon Marchi <simark@simark.ca> wrote:
> >
> > On 2019-08-15 2:49 p.m., Christian Biesinger via gdb-patches wrote:
> > > PyFile_FromString and PyFile_AsFile have been removed in Python 3.
> > > There is no obvious replacement that works here, and we can't just
> > > pass our FILE* to a DLL in Windows because it may use a different
> > > C runtime.
> > >
> > > So we just call a Python function which reads and executes file
> > > contents. Care must be taken to execute it in the context of
> > > __main__.
> > >
> > > Tested by inverting the ifdef and running the testsuite on Debian
> > > Linux (even without the patch, I failed at running the testsuite
> > > on Windows). I did test with both Python 2 and 3.
[...]
> > The patch LGTM with this fixed.
>
> Thanks, pushing now with that fixed.

Thinking about this patch -- is it worth a NEWS entry to mention that
gdb can now be compiled with Python 3 on Windows?

Christian
  

> From: "Christian Biesinger via gdb-patches" <gdb-patches@sourceware.org>
> Date: Sat, 14 Sep 2019 09:08:51 -0400
> Cc: gdb-patches <gdb-patches@sourceware.org>
> 
> Thinking about this patch -- is it worth a NEWS entry to mention that
> gdb can now be compiled with Python 3 on Windows?

You are right, it probably is.