Re: [PATCH] Fix python-interactive with Python 3.6

[Pedro Alves <palves@redhat.com>]

On 01/20/2017 03:15 PM, Simon Marchi wrote:
> Since Python 3.4, the callback installed in PyOS_ReadlineFunctionPointer
> should return a value allocated with PyMem_RawMalloc instead of
> PyMem_Malloc.  The reason is that PyMem_Malloc must be called with the
> Python Global Interpreter Lock (GIL) held, which is not the case in the
> context where this function is called.  PyMem_RawMalloc was introduced
> for cases like this.
> 

> +/* Starting from Python 3.4, the result of the PyOS_ReadlineFunctionPointer
> +   callback must be allocated with PyMem_RawMalloc rather than PyMem_Malloc.  */
> +
> +#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION >= 4

This will break with PY_MAJOR_VERSION 4 (at some point :-) ).
Write:

 #if PY_MAJOR_VERSION > 3 
     || (PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION >= 4)

?

Or add some macro that makes it a bit easier to write,
like "#if HAVE_PY_AT_LEAST(3, 4)" or
"#if GDB_PY_VERSION >= 3004" (like GCC_VERSION).
Or use Python's PY_VERSION_HEX, like
"#if PY_VERSION_HEX >= 0x03040000".

> +#define PyOS_ReadlineFunctionPointer_Malloc PyMem_RawMalloc
> +#else
> +#define PyOS_ReadlineFunctionPointer_Malloc PyMem_Malloc
> +#endif

It sounds like we'll find other cases that will need
to call PyMem_RawMalloc going forward?  How about handling
this similarly to how we handle fixing up other missing
Python bits, in python-internal.h.  Like:

#if python < 3.4

static inline void *
gdb_PyMem_RawMalloc (size_t n)
{
  return gdb_PyMem_Malloc (n);
}
#define PyMem_RawMalloc(n) gdb_PyMem_RawMalloc (n)

#endif

> +
>  /* Readline function suitable for PyOS_ReadlineFunctionPointer, which
>     is used for Python's interactive parser and raw_input.  In both
>     cases, sys_stdin and sys_stdout are always stdin and stdout
> @@ -63,7 +73,7 @@ gdbpy_readline_wrapper (FILE *sys_stdin, FILE *sys_stdout,
>    /* Detect EOF (Ctrl-D).  */
>    if (p == NULL)
>      {
> -      q = (char *) PyMem_Malloc (1);
> +      q = (char *) PyOS_ReadlineFunctionPointer_Malloc (1);

and then write PyMem_RawMalloc here.

Thanks,
Pedro Alves