configure uses incorrect link order when testing libpython

References:

https://stackoverflow.com/a/49868387
https://sourceware.org/bugzilla/show_bug.cgi?id=11420

Configure uses "gcc -o conftest -g ... conftest.c -ldl -lncurses -lm -ldl
... -lpthread ... -lpython2.7" when deciding whether give libpython is
usable.

That of course is the wrong link order, and only works for shared libraries
(mostly by accident), and only on some systems.

gdb/ChangeLog:

	PR gdb/11420
	* configure.ac: Prepend libpython.
	* python/python-config.py: Likewise.
	* configure: Regenerate.

4 files changed, 22 insertions, 16 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 1a44240..c20f2a9 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2018-05-04  Paul Pluzhnikov  <ppluzhnikov@google.com>
+
+	PR gdb/11420
+	* configure.ac: Prepend libpython.
+	* python/python-config.py: Likewise.
+	* configure: Regenerate.
+
 2018-05-03  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* Makefile.in (%.c: %.l): Use -t instead of --stdout.
diff --git a/gdb/configure b/gdb/configure
index f18d78e..1aac930 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -10441,7 +10441,7 @@ $as_echo_n "checking for ${version}... " >&6; }
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -10478,13 +10478,13 @@ $as_echo "${found_usable_python}" >&6; }
   version=python2.7
 
   new_CPPFLAGS=${python_includes}
-  new_LIBS="${python_libs} -lpython2.7"
+  new_LIBS="-lpython2.7 ${python_libs}"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${version}" >&5
 $as_echo_n "checking for ${version}... " >&6; }
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -10516,13 +10516,13 @@ $as_echo "${found_usable_python}" >&6; }
   version=python2.6
 
   new_CPPFLAGS=${python_includes}
-  new_LIBS="${python_libs} -lpython2.6"
+  new_LIBS="-lpython2.6 ${python_libs}"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${version}" >&5
 $as_echo_n "checking for ${version}... " >&6; }
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -10554,13 +10554,13 @@ $as_echo "${found_usable_python}" >&6; }
   version=python2.5
 
   new_CPPFLAGS=${python_includes}
-  new_LIBS="${python_libs} -lpython2.5"
+  new_LIBS="-lpython2.5 ${python_libs}"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${version}" >&5
 $as_echo_n "checking for ${version}... " >&6; }
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
@@ -10592,13 +10592,13 @@ $as_echo "${found_usable_python}" >&6; }
   version=python2.4
 
   new_CPPFLAGS=${python_includes}
-  new_LIBS="${python_libs} -lpython2.4"
+  new_LIBS="-lpython2.4 ${python_libs}"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for ${version}" >&5
 $as_echo_n "checking for ${version}... " >&6; }
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
diff --git a/gdb/configure.ac b/gdb/configure.ac
index 698fc7b..e1f630c 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -732,7 +732,7 @@ AC_DEFUN([AC_TRY_LIBPYTHON],
   save_CPPFLAGS=$CPPFLAGS
   save_LIBS=$LIBS
   CPPFLAGS="$CPPFLAGS $new_CPPFLAGS"
-  LIBS="$LIBS $new_LIBS"
+  LIBS="$new_LIBS $LIBS"
   found_usable_python=no
   AC_LINK_IFELSE(AC_LANG_PROGRAM([[#include "Python.h"]],
                                  [[Py_Initialize ();]]),
@@ -922,19 +922,19 @@ else
   elif test "${have_python_config}" != failed; then
     if test "${have_libpython}" = no; then
       AC_TRY_LIBPYTHON(python2.7, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.7")
+                       ${python_includes}, "-lpython2.7 ${python_libs}")
     fi
     if test "${have_libpython}" = no; then
       AC_TRY_LIBPYTHON(python2.6, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.6")
+                       ${python_includes}, "-lpython2.6 ${python_libs}")
     fi
     if test ${have_libpython} = no; then
       AC_TRY_LIBPYTHON(python2.5, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.5")
+                       ${python_includes}, "-lpython2.5 ${python_libs}")
     fi
     if test ${have_libpython} = no; then
       AC_TRY_LIBPYTHON(python2.4, have_libpython,
-                       ${python_includes}, "${python_libs} -lpython2.4")
+                       ${python_includes}, "-lpython2.4 ${python_libs}")
     fi
   fi
   if test "${have_libpython}" = python2.7 -o "${have_libpython}" = python27; then
diff --git a/gdb/python/python-config.py b/gdb/python/python-config.py
index c2b2969..3e60b86 100644
--- a/gdb/python/python-config.py
+++ b/gdb/python/python-config.py
@@ -58,12 +58,11 @@ for opt in opt_flags:
         print (to_unix_path(' '.join(flags)))
 
     elif opt in ('--libs', '--ldflags'):
-        libs = []
+        libs = ['-lpython' + pyver + abiflags]
         if getvar('LIBS') is not None:
             libs.extend(getvar('LIBS').split())
         if getvar('SYSLIBS') is not None:
             libs.extend(getvar('SYSLIBS').split())
-        libs.append('-lpython'+pyver + abiflags)
         # add the prefix/lib/pythonX.Y/config dir, but only if there is no
         # shared library in prefix/lib/.
         if opt == '--ldflags':