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

Jan Kratochvil
2015-02-04T17:43:24Z

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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

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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