build,qt: Build Qt with -fPIC if required or requested

* configure.ac: Add option to enable building the Qt 6 binding with
-fPIC. Fix typo and mention default for --enable-no-direct-extern-access
option.
* m4/qt6.m4: Add -fPIC to GPGME_QT6_CFLAGS if requested or if Qt 6 was
built with reduce_relocations.
--

GnuPG-bug-id: 6781

NEWS

@@ -4,6 +4,9 @@ Noteworthy changes in version 1.23.2 (unreleased)
  * qt: Use a temporary file name when creating signed or encrypted
    archives. [T6721]
 
+ * qt: Build Qt 6 bindings with -fPIC if requested or Qt 6 was built with
+   this flag. [T6781]
+
 
 Noteworthy changes in version 1.23.1 (2023-10-27)
 -------------------------------------------------

configure.ac

@@ -338,6 +338,18 @@ if test x$fixed_search_path != x ; then
                     [Locate binaries only via this PATH])
 fi
 
+# Option --enable-reduce-relocations
+#
+# Allow building the Qt 6 bindings explicitly with -fPIC if the automatic
+# detection fails. Note: We assume that this flag is always available (unless
+# we built for Windows).
+AC_ARG_ENABLE([reduce-relocations],
+              AS_HELP_STRING([--enable-reduce-relocations],
+                             [build Qt 6 bindings with -fPIC (default is
+                              auto)]),
+              [use_reduce_relocations="$enableval"],
+              [use_reduce_relocations=""])
+
 # Option --enable-no-direct-extern-access
 #
 # Some distributions build Qt 6 with -mno-direct-extern-access. Libraries and
@@ -352,8 +364,8 @@ AX_CHECK_COMPILE_FLAG([-mno-direct-extern-access],
 AC_LANG_POP()
 AC_ARG_ENABLE([no-direct-extern-access],
               AS_HELP_STRING([--enable-no-direct-extern-access],
-                             [build Qt 6 bindinds with
+                             [build Qt 6 bindings with
-                              -mno-direct-extern-access]),
+                              -mno-direct-extern-access (default is auto)]),
               [use_no_direct_extern_access="$enableval"],
               [use_no_direct_extern_access=""])
 

m4/qt6.m4

@@ -34,10 +34,30 @@ AC_DEFUN([FIND_QT6],
   fi
 
   if test "$have_qt6_libs" = "yes"; then
-    if test "$have_no_direct_extern_access" = yes; then
+    if test "$have_w32_system" != yes; then
-      if test -z "$use_no_direct_extern_access" && test "$have_w32_system" != yes; then
       mkspecsdir=$($PKG_CONFIG --variable mkspecsdir Qt6Platform)
-        if test -n "$mkspecsdir"; then
+      if test -z "$mkspecsdir"; then
+        AC_MSG_WARN([Failed to determine Qt's mkspecs directory. Cannot check its build configuration.])
+      fi
+    fi
+
+    # check if we need -fPIC
+    if test -z "$use_reduce_relocations" && test -n "$mkspecsdir"; then
+      AC_MSG_CHECKING([whether Qt was built with -fPIC])
+      if grep -q "QT_CONFIG .* reduce_relocations" $mkspecsdir/qconfig.pri; then
+        use_reduce_relocations="yes"
+      else
+        use_reduce_relocations="no"
+      fi
+      AC_MSG_RESULT([$use_reduce_relocations])
+    fi
+    if test "$use_reduce_relocations" = yes; then
+      GPGME_QT6_CFLAGS="$GPGME_QT6_CFLAGS -fPIC"
+    fi
+
+    # check if we need -mno-direct-extern-access
+    if test "$have_no_direct_extern_access" = yes; then
+      if test -z "$use_no_direct_extern_access" && test -n "$mkspecsdir"; then
         AC_MSG_CHECKING([whether Qt was built with -mno-direct-extern-access])
         if grep -q "QT_CONFIG .* no_direct_extern_access" $mkspecsdir/qconfig.pri; then
           use_no_direct_extern_access="yes"
@@ -45,9 +65,6 @@ AC_DEFUN([FIND_QT6],
           use_no_direct_extern_access="no"
         fi
         AC_MSG_RESULT([$use_no_direct_extern_access])
-        else
-          AC_MSG_WARN([Failed to determine Qt's mkspecs directory. Cannot check its build configuration.])
-        fi
       fi
       if test "$use_no_direct_extern_access" = yes; then
         GPGME_QT6_CFLAGS="$GPGME_QT6_CFLAGS -mno-direct-extern-access"