[patch] Fix Python 3 build error on 32-bit hosts

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

on Fedora Rawhide (==22) i686 using --with-python=/usr/bin/python3 one gets:

gcc -g   -I. -I. -I./common -I./config -DLOCALEDIR="\"/usr/local/share/locale\"" -DHAVE_CONFIG_H -I./../include/opcode -I./../opcodes/.. -I./../readline/.. -I../bfd -I./../bfd -I./../include -I../libdecnumber -I./../libdecnumber  -I./gnulib/import -Ibuild-gnulib/import   -DTUI=1   -pthread -I/usr/include/guile/2.0  -I/usr/include/python3.4m -I/usr/include/python3.4m -Wall -Wdeclaration-after-statement -Wpointer-arith -Wpointer-sign -Wno-unused -Wunused-value -Wunused-function -Wno-switch -Wno-char-subscripts -Wmissing-prototypes -Wdeclaration-after-statement -Wempty-body -Wmissing-parameter-type -Wold-style-declaration -Wold-style-definition -Wformat-nonliteral -Werror -c -o py-value.o -MT py-value.o -MMD -MP -MF .deps/py-value.Tpo -fno-strict-aliasing -DNDEBUG -fwrapv ./python/py-value.c
./python/py-value.c:1696:3: error: initialization from incompatible pointer type [-Werror]
   valpy_hash,            /*tp_hash*/
   ^
./python/py-value.c:1696:3: error: (near initialization for ‘value_object_type.tp_hash’) [-Werror]
cc1: all warnings being treated as errors
Makefile:2628: recipe for target 'py-value.o' failed

This is because in Python 2 tp_hash was:
	typedef long (*hashfunc)(PyObject *);
while in Python 3 tp_hash is:
	typedef Py_hash_t (*hashfunc)(PyObject *);

Py_hash_t is int for 32-bit hosts and long for 64-bit hosts.  While on 32-bit
hosts sizeof(long)==sizeof(int) still the hashfunc type is formally
incompatible.  As this patch should have no compiled code change it is not
really necessary for gdb-7.9, it would fix there just this non-fatal
compilation warning:
	./python/py-value.c:1696:3: warning: initialization from incompatible pointer type
	   valpy_hash,            /*tp_hash*/
	   ^
	./python/py-value.c:1696:3: warning: (near initialization for ‘value_object_type.tp_hash’)

A question is whether the autoconf test isn't an overkill.  One could use
instead just:
	#if PYTHON_ABI_VERSION >= 3
Also one could use that #if either just at the valpy_hash() definition or one
could provide Py_hash_t in gdb/defs.h or one could provide some GDB_Py_hash_t
in gdb/defs.h.

Tested compilation with:
	python-devel-2.7.9-4.fc22.x86_64
	python-devel-2.7.9-4.fc22.i686
	python3-devel-3.4.2-4.fc22.x86_64
	python3-devel-3.4.2-4.fc22.i686


Jan

gdb/
2015-02-04  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* configure.ac <"${have_libpython}" != no>: Define Py_hash_t.
	* python/py-value.c (valpy_fetch_lazy): Use it.  Remove cast to the
	return type.
	* config.in: Regenerate.
	* configure: Regenerate.

diff --git a/gdb/configure.ac b/gdb/configure.ac
index dfc6947..f335b7b 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1016,6 +1016,25 @@ if test "${have_libpython}" != no; then
   ]]), [python_has_threads=no], [python_has_threads=yes])
   AC_MSG_RESULT(${python_has_threads})
   CPPFLAGS="${saved_CPPFLAGS}"
+
+  AC_CACHE_CHECK([for Py_hash_t], gdb_cv_Py_hash_t,
+    old_CFLAGS="$CFLAGS"
+    CFLAGS="$CFLAGS $PYTHON_CFLAGS"
+    old_CPPFLAGS="$CPPFLAGS"
+    CPPFLAGS="$CPPFLAGS $PYTHON_CPPFLAGS"
+    AC_TRY_COMPILE(
+      [#include <Python.h>],
+      [Py_hash_t var;],
+      gdb_cv_Py_hash_t=yes,
+      gdb_cv_Py_hash_t=no
+    )
+    CPPFLAGS="$old_CPPFLAGS"
+    CFLAGS="$old_CFLAGS"
+  )
+  if test "x$gdb_cv_Py_hash_t" = "xno"; then
+    AC_DEFINE(Py_hash_t, long,
+	      [Provide Python 3 Py_hash_t for Python 2.])
+  fi
 else
   # Even if Python support is not compiled in, we need to have this file
   # included so that the "python" command, et.al., still exists.
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 4c4d36e..5a13777 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -895,10 +895,10 @@ valpy_fetch_lazy (PyObject *self, PyObject *args)
 
 /* Calculate and return the address of the PyObject as the value of
    the builtin __hash__ call.  */
-static long
+static Py_hash_t
 valpy_hash (PyObject *self)
 {
-  return (long) (intptr_t) self;
+  return (intptr_t) self;
 }
 
 enum valpy_opcode