iOS: Use in-place string renaming to rename main() instead of ld

Processing the object file with ld strips away debug information for
the main() function, resulting in the debugger not being able to
break on specific lines of the function.

It also causes issues when externing sybols in main's object file.

We revert back to the approach of using the strings in-line in the
object file (which is why we keep the name the same length, 'qtmn').

Task-number: QTBUG-35553
Change-Id: I8b0acee36f48ecfefa2e4fd008a842365713d985
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

mkspecs/macx-ios-clang/features/qt.prf

@@ -42,12 +42,7 @@ equals(TEMPLATE, app):contains(QT, gui(-private)?) {
         !isEmpty(QMAKE_PRE_LINK): \
             QMAKE_PRE_LINK += ";"
 
-        QMAKE_PRE_LINK += \
-            "for f in $(find $${objects_dir} -name '*.o'); do" \
-                "(nm $f | grep -q 'T _main' && cp $f $f.original" \
-                    "&& ld -r -alias _main _qt_main -unexported_symbol _main $f.original -o $f)" \
-                "|| true" \
-            "; done"
+        QMAKE_PRE_LINK += $$QMAKESPEC/rename_main.sh $${objects_dir}
     }
 }
 

mkspecs/macx-ios-clang/rename_main.sh

@@ -0,0 +1,63 @@
+#!/bin/bash
+
+#############################################################################
+##
+## Copyright (C) 2014 Digia Plc and/or its subsidiary(-ies).
+## Contact: http://www.qt-project.org/legal
+##
+## This file is the build configuration utility of the Qt Toolkit.
+##
+## $QT_BEGIN_LICENSE:LGPL$
+## Commercial License Usage
+## Licensees holding valid commercial Qt licenses may use this file in
+## accordance with the commercial license agreement provided with the
+## Software or, alternatively, in accordance with the terms contained in
+## a written agreement between you and Digia.  For licensing terms and
+## conditions see http://qt.digia.com/licensing.  For further information
+## use the contact form at http://qt.digia.com/contact-us.
+##
+## GNU Lesser General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU Lesser
+## General Public License version 2.1 as published by the Free Software
+## Foundation and appearing in the file LICENSE.LGPL included in the
+## packaging of this file.  Please review the following information to
+## ensure the GNU Lesser General Public License version 2.1 requirements
+## will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+##
+## In addition, as a special exception, Digia gives you certain additional
+## rights.  These rights are described in the Digia Qt LGPL Exception
+## version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+##
+## GNU General Public License Usage
+## Alternatively, this file may be used under the terms of the GNU
+## General Public License version 3.0 as published by the Free Software
+## Foundation and appearing in the file LICENSE.GPL included in the
+## packaging of this file.  Please review the following information to
+## ensure the GNU General Public License version 3.0 requirements will be
+## met: http://www.gnu.org/copyleft/gpl.html.
+##
+##
+## $QT_END_LICENSE$
+##
+#############################################################################
+
+if [ $# -eq 0 ]; then
+    echo "usage: $0 <path to object files>"
+else
+    for f in $(find $1 -name '*.o'); do
+        # Skip object files without the _main symbol
+        nm $f | grep -q 'T _main$' || continue
+
+        echo "Found main() in ${f#$1/}"
+
+        strings -t d - $f | grep '_main\(\.eh\)\?$' | while read match; do
+            offset=$(echo $match | cut -d ' ' -f 1)
+            symbol=$(echo $match | cut -d ' ' -f 2)
+
+            echo "  Renaming '$symbol' at offset $offset to '${symbol/main/qtmn}'"
+
+            # In-place rename the string (keeping the same length)
+            printf '_qtmn' | dd of=$f bs=1 seek=$offset conv=notrunc >/dev/null 2>&1
+        done
+    done
+fi

src/plugins/platforms/ios/qioseventdispatcher.mm

@@ -246,7 +246,7 @@ enum SetJumpResult
 // user our main wrapper. Since the symbol is weak, it will not
 // get used or cause a clash in the normal Qt application usecase,
 // where we rename main to qt_main.
-extern "C" int __attribute__((weak)) qt_main(int argc, char *argv[])
+extern "C" int __attribute__((weak)) qtmn(int argc, char *argv[])
 {
     Q_UNUSED(argc);
     Q_UNUSED(argv);
@@ -265,7 +265,7 @@ static void __attribute__((noinline, noreturn)) user_main_trampoline()
         strcpy(argv[i], [arg cStringUsingEncoding:[NSString defaultCStringEncoding]]);
     }
 
-    int exitCode = qt_main(argc, argv);
+    int exitCode = qtmn(argc, argv);
     delete[] argv;
 
     qEventDispatcherDebug() << "Returned from main with exit code " << exitCode;