[PATCH v3 2/7] gdb: fail configure if Python version is too old for limited API

[Matthieu Longo <matthieu.longo@arm.com>]

GDB can be built against the Python limited API using the configure
flag '--enable-py-limited-api=yes'. This flag is currently experimental,
and the build is not yet fully successful. Today, the minimum required
Python version for this option is 3.11. This requirement is not final
and will be raised to a later version as the migration progresses.

However, the configure script does not currently report an error if an
older version of Python is used. Instead, the build fails later with
numerous errors that are difficult to relate to Python limited API
compatiblity.

This patch adds a version check when '--enable-py-limited-api=yes' is
specified, ensuring that the provided Python version meets the minimum
requirements for the limited API support. If it does not, configure will
now fail with a clear error message.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=23830
---
 gdb/aclocal.m4   | 253 +++++++++++++++++++++++++++++++++++++++++++++++
 gdb/configure    |  27 ++++-
 gdb/configure.ac |  20 +++-
 3 files changed, 294 insertions(+), 6 deletions(-)

diff --git a/gdb/aclocal.m4 b/gdb/aclocal.m4
index cae09708e01..254cb4edadc 100644
--- a/gdb/aclocal.m4
+++ b/gdb/aclocal.m4
@@ -154,6 +154,259 @@ AC_MSG_CHECKING([whether to enable maintainer-specific portions of Makefiles])
 ]
 )
 
+# Copyright (C) 1999-2017 Free Software Foundation, Inc.
+#
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+
+# AM_PATH_PYTHON([MINIMUM-VERSION], [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
+# ---------------------------------------------------------------------------
+# Adds support for distributing Python modules and packages.  To
+# install modules, copy them to $(pythondir), using the python_PYTHON
+# automake variable.  To install a package with the same name as the
+# automake package, install to $(pkgpythondir), or use the
+# pkgpython_PYTHON automake variable.
+#
+# The variables $(pyexecdir) and $(pkgpyexecdir) are provided as
+# locations to install python extension modules (shared libraries).
+# Another macro is required to find the appropriate flags to compile
+# extension modules.
+#
+# If your package is configured with a different prefix to python,
+# users will have to add the install directory to the PYTHONPATH
+# environment variable, or create a .pth file (see the python
+# documentation for details).
+#
+# If the MINIMUM-VERSION argument is passed, AM_PATH_PYTHON will
+# cause an error if the version of python installed on the system
+# doesn't meet the requirement.  MINIMUM-VERSION should consist of
+# numbers and dots only.
+AC_DEFUN([AM_PATH_PYTHON],
+ [
+  dnl Find a Python interpreter.  Python versions prior to 2.0 are not
+  dnl supported. (2.0 was released on October 16, 2000).
+  dnl FIXME: Remove the need to hard-code Python versions here.
+  m4_define_default([_AM_PYTHON_INTERPRETER_LIST],
+[python python2 python3 python3.5 python3.4 python3.3 python3.2 python3.1 python3.0 python2.7 dnl
+ python2.6 python2.5 python2.4 python2.3 python2.2 python2.1 python2.0])
+
+  AC_ARG_VAR([PYTHON], [the Python interpreter])
+
+  m4_if([$1],[],[
+    dnl No version check is needed.
+    # Find any Python interpreter.
+    if test -z "$PYTHON"; then
+      AC_PATH_PROGS([PYTHON], _AM_PYTHON_INTERPRETER_LIST, :)
+    fi
+    am_display_PYTHON=python
+  ], [
+    dnl A version check is needed.
+    if test -n "$PYTHON"; then
+      # If the user set $PYTHON, use it and don't search something else.
+      AC_MSG_CHECKING([whether $PYTHON version is >= $1])
+      AM_PYTHON_CHECK_VERSION([$PYTHON], [$1],
+			      [AC_MSG_RESULT([yes])],
+			      [AC_MSG_RESULT([no])
+			       AC_MSG_ERROR([Python interpreter is too old])])
+      am_display_PYTHON=$PYTHON
+    else
+      # Otherwise, try each interpreter until we find one that satisfies
+      # VERSION.
+      AC_CACHE_CHECK([for a Python interpreter with version >= $1],
+	[am_cv_pathless_PYTHON],[
+	for am_cv_pathless_PYTHON in _AM_PYTHON_INTERPRETER_LIST none; do
+	  test "$am_cv_pathless_PYTHON" = none && break
+	  AM_PYTHON_CHECK_VERSION([$am_cv_pathless_PYTHON], [$1], [break])
+	done])
+      # Set $PYTHON to the absolute path of $am_cv_pathless_PYTHON.
+      if test "$am_cv_pathless_PYTHON" = none; then
+	PYTHON=:
+      else
+        AC_PATH_PROG([PYTHON], [$am_cv_pathless_PYTHON])
+      fi
+      am_display_PYTHON=$am_cv_pathless_PYTHON
+    fi
+  ])
+
+  if test "$PYTHON" = :; then
+  dnl Run any user-specified action, or abort.
+    m4_default([$3], [AC_MSG_ERROR([no suitable Python interpreter found])])
+  else
+
+  dnl Query Python for its version number.  Getting [:3] seems to be
+  dnl the best way to do this; it's what "site.py" does in the standard
+  dnl library.
+
+  AC_CACHE_CHECK([for $am_display_PYTHON version], [am_cv_python_version],
+    [am_cv_python_version=`$PYTHON -c "import sys; sys.stdout.write(sys.version[[:3]])"`])
+  AC_SUBST([PYTHON_VERSION], [$am_cv_python_version])
+
+  dnl Use the values of $prefix and $exec_prefix for the corresponding
+  dnl values of PYTHON_PREFIX and PYTHON_EXEC_PREFIX.  These are made
+  dnl distinct variables so they can be overridden if need be.  However,
+  dnl general consensus is that you shouldn't need this ability.
+
+  AC_SUBST([PYTHON_PREFIX], ['${prefix}'])
+  AC_SUBST([PYTHON_EXEC_PREFIX], ['${exec_prefix}'])
+
+  dnl At times (like when building shared libraries) you may want
+  dnl to know which OS platform Python thinks this is.
+
+  AC_CACHE_CHECK([for $am_display_PYTHON platform], [am_cv_python_platform],
+    [am_cv_python_platform=`$PYTHON -c "import sys; sys.stdout.write(sys.platform)"`])
+  AC_SUBST([PYTHON_PLATFORM], [$am_cv_python_platform])
+
+  # Just factor out some code duplication.
+  am_python_setup_sysconfig="\
+import sys
+# Prefer sysconfig over distutils.sysconfig, for better compatibility
+# with python 3.x.  See automake bug#10227.
+try:
+    import sysconfig
+except ImportError:
+    can_use_sysconfig = 0
+else:
+    can_use_sysconfig = 1
+# Can't use sysconfig in CPython 2.7, since it's broken in virtualenvs:
+# <https://github.com/pypa/virtualenv/issues/118>
+try:
+    from platform import python_implementation
+    if python_implementation() == 'CPython' and sys.version[[:3]] == '2.7':
+        can_use_sysconfig = 0
+except ImportError:
+    pass"
+
+  dnl Set up 4 directories:
+
+  dnl pythondir -- where to install python scripts.  This is the
+  dnl   site-packages directory, not the python standard library
+  dnl   directory like in previous automake betas.  This behavior
+  dnl   is more consistent with lispdir.m4 for example.
+  dnl Query distutils for this directory.
+  AC_CACHE_CHECK([for $am_display_PYTHON script directory],
+    [am_cv_python_pythondir],
+    [if test "x$prefix" = xNONE
+     then
+       am_py_prefix=$ac_default_prefix
+     else
+       am_py_prefix=$prefix
+     fi
+     am_cv_python_pythondir=`$PYTHON -c "
+$am_python_setup_sysconfig
+if can_use_sysconfig:
+    sitedir = sysconfig.get_path('purelib', vars={'base':'$am_py_prefix'})
+else:
+    from distutils import sysconfig
+    sitedir = sysconfig.get_python_lib(0, 0, prefix='$am_py_prefix')
+sys.stdout.write(sitedir)"`
+     case $am_cv_python_pythondir in
+     $am_py_prefix*)
+       am__strip_prefix=`echo "$am_py_prefix" | sed 's|.|.|g'`
+       am_cv_python_pythondir=`echo "$am_cv_python_pythondir" | sed "s,^$am__strip_prefix,$PYTHON_PREFIX,"`
+       ;;
+     *)
+       case $am_py_prefix in
+         /usr|/System*) ;;
+         *)
+	  am_cv_python_pythondir=$PYTHON_PREFIX/lib/python$PYTHON_VERSION/site-packages
+	  ;;
+       esac
+       ;;
+     esac
+    ])
+  AC_SUBST([pythondir], [$am_cv_python_pythondir])
+
+  dnl pkgpythondir -- $PACKAGE directory under pythondir.  Was
+  dnl   PYTHON_SITE_PACKAGE in previous betas, but this naming is
+  dnl   more consistent with the rest of automake.
+
+  AC_SUBST([pkgpythondir], [\${pythondir}/$PACKAGE])
+
+  dnl pyexecdir -- directory for installing python extension modules
+  dnl   (shared libraries)
+  dnl Query distutils for this directory.
+  AC_CACHE_CHECK([for $am_display_PYTHON extension module directory],
+    [am_cv_python_pyexecdir],
+    [if test "x$exec_prefix" = xNONE
+     then
+       am_py_exec_prefix=$am_py_prefix
+     else
+       am_py_exec_prefix=$exec_prefix
+     fi
+     am_cv_python_pyexecdir=`$PYTHON -c "
+$am_python_setup_sysconfig
+if can_use_sysconfig:
+    sitedir = sysconfig.get_path('platlib', vars={'platbase':'$am_py_prefix'})
+else:
+    from distutils import sysconfig
+    sitedir = sysconfig.get_python_lib(1, 0, prefix='$am_py_prefix')
+sys.stdout.write(sitedir)"`
+     case $am_cv_python_pyexecdir in
+     $am_py_exec_prefix*)
+       am__strip_prefix=`echo "$am_py_exec_prefix" | sed 's|.|.|g'`
+       am_cv_python_pyexecdir=`echo "$am_cv_python_pyexecdir" | sed "s,^$am__strip_prefix,$PYTHON_EXEC_PREFIX,"`
+       ;;
+     *)
+       case $am_py_exec_prefix in
+         /usr|/System*) ;;
+         *)
+	   am_cv_python_pyexecdir=$PYTHON_EXEC_PREFIX/lib/python$PYTHON_VERSION/site-packages
+	   ;;
+       esac
+       ;;
+     esac
+    ])
+  AC_SUBST([pyexecdir], [$am_cv_python_pyexecdir])
+
+  dnl pkgpyexecdir -- $(pyexecdir)/$(PACKAGE)
+
+  AC_SUBST([pkgpyexecdir], [\${pyexecdir}/$PACKAGE])
+
+  dnl Run any user-specified action.
+  $2
+  fi
+
+])
+
+
+# AM_PYTHON_CHECK_VERSION(PROG, VERSION, [ACTION-IF-TRUE], [ACTION-IF-FALSE])
+# ---------------------------------------------------------------------------
+# Run ACTION-IF-TRUE if the Python interpreter PROG has version >= VERSION.
+# Run ACTION-IF-FALSE otherwise.
+# This test uses sys.hexversion instead of the string equivalent (first
+# word of sys.version), in order to cope with versions such as 2.2c1.
+# This supports Python 2.0 or higher. (2.0 was released on October 16, 2000).
+AC_DEFUN([AM_PYTHON_CHECK_VERSION],
+ [prog="import sys
+# split strings by '.' and convert to numeric.  Append some zeros
+# because we need at least 4 digits for the hex conversion.
+# map returns an iterator in Python 3.0 and a list in 2.x
+minver = list(map(int, '$2'.split('.'))) + [[0, 0, 0]]
+minverhex = 0
+# xrange is not present in Python 3.0 and range returns an iterator
+for i in list(range(0, 4)): minverhex = (minverhex << 8) + minver[[i]]
+sys.exit(sys.hexversion < minverhex)"
+  AS_IF([AM_RUN_LOG([$1 -c "$prog"])], [$3], [$4])])
+
+# Copyright (C) 2001-2017 Free Software Foundation, Inc.
+#
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# AM_RUN_LOG(COMMAND)
+# -------------------
+# Run COMMAND, save the exit status in ac_status, and log it.
+# (This has been adapted from Autoconf's _AC_RUN_LOG macro.)
+AC_DEFUN([AM_RUN_LOG],
+[{ echo "$as_me:$LINENO: $1" >&AS_MESSAGE_LOG_FD
+   ($1) >&AS_MESSAGE_LOG_FD 2>&AS_MESSAGE_LOG_FD
+   ac_status=$?
+   echo "$as_me:$LINENO: \$? = $ac_status" >&AS_MESSAGE_LOG_FD
+   (exit $ac_status); }])
+
 # Copyright (C) 2001-2017 Free Software Foundation, Inc.
 #
 # This file is free software; the Free Software Foundation
diff --git a/gdb/configure b/gdb/configure
index 12c54521682..dcd5c030713 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -28507,6 +28507,7 @@ fi
     # do except assume that the compiler will be able to find those files.
     python_includes=
     python_libs=
+    python_prefix=
     have_python_config=no
   fi
 
@@ -28743,6 +28744,7 @@ else
 fi
 
 
+
 # Check whether to build GDB against Python limited C API.
 # Check whether --enable-py-limited-api was given.
 if test "${enable_py_limited_api+set}" = set; then :
@@ -28763,11 +28765,32 @@ fi
 if test "$enable_py_limited_api" = yes; then
   # The minimal Python limited API version is currently set to 3.11 for the
   # support of PyBuffer_FillInfo and PyBuffer_Release.
-  # The choice of the minimal version for the Python limited API won't be frozen
-  # until the end of the migration.
+  # The choice of the minimal version for the Python limited API won't be
+  # frozen until the end of the migration.
+  prog="import sys
+# split strings by '.' and convert to numeric.  Append some zeros
+# because we need at least 4 digits for the hex conversion.
+# map returns an iterator in Python 3.0 and a list in 2.x
+minver = list(map(int, '3.11'.split('.'))) + [0, 0, 0]
+minverhex = 0
+# xrange is not present in Python 3.0 and range returns an iterator
+for i in list(range(0, 4)): minverhex = (minverhex << 8) + minver[i]
+sys.exit(sys.hexversion < minverhex)"
+  if { echo "$as_me:$LINENO: $python_prog -c "$prog"" >&5
+   ($python_prog -c "$prog") >&5 2>&5
+   ac_status=$?
+   echo "$as_me:$LINENO: \$? = $ac_status" >&5
+   (exit $ac_status); }; then :
+
 
 $as_echo "#define Py_LIMITED_API 0x030b0000" >>confdefs.h
 
+
+else
+
+      as_fn_error $? "Python limited API support requires at least Python version 3.11" "$LINENO" 5
+
+fi
 fi
 
 # -------------------- #
diff --git a/gdb/configure.ac b/gdb/configure.ac
index cf8078e1d89..17f648d0b49 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -933,6 +933,7 @@ else
     # do except assume that the compiler will be able to find those files.
     python_includes=
     python_libs=
+    python_prefix=
     have_python_config=no
   fi
 
@@ -1062,6 +1063,13 @@ AC_SUBST(PYTHON_CPPFLAGS)
 AC_SUBST(PYTHON_LIBS)
 AM_CONDITIONAL(HAVE_PYTHON, test "${have_libpython}" != no)
 
+dnl Use --enable-py-limited-api to enable the build of GDB against the Python
+dnl limited API.
+dnl
+dnl no -   Disable the Python limited API.
+dnl yes -  Use the Python limited API to build GDB, error if the selected
+dnl        version of Python is not compatible with the Python limited API.
+
 # Check whether to build GDB against Python limited C API.
 AC_ARG_ENABLE([py-limited-api],
 	      [AS_HELP_STRING([--enable-py-limited-api],
@@ -1072,10 +1080,14 @@ AC_ARG_ENABLE([py-limited-api],
 if test "$enable_py_limited_api" = yes; then
   # The minimal Python limited API version is currently set to 3.11 for the
   # support of PyBuffer_FillInfo and PyBuffer_Release.
-  # The choice of the minimal version for the Python limited API won't be frozen
-  # until the end of the migration.
-  AC_DEFINE(Py_LIMITED_API, 0x030b0000,
-	    [Define if GDB should be built against the Python limited C API.])
+  # The choice of the minimal version for the Python limited API won't be
+  # frozen until the end of the migration.
+  AM_PYTHON_CHECK_VERSION([$python_prog], [3.11], [
+    AC_DEFINE(Py_LIMITED_API, 0x030b0000,
+      [Define if GDB should be built against the Python limited C API.])
+    ],[
+      AC_MSG_ERROR([Python limited API support requires at least Python version 3.11])
+    ])
 fi
 
 # -------------------- #
-- 
2.53.0