Make qglobal.h complain if you use -fPIE

Prior to Qt 5.4.2 (commit 36d6eb7), we allowed it, but now we need to enforce that it is not used. Note that -fPIE does define __PIC__, so we need this to catch the use of -fPIE. [ChangeLog][Important Behavior Changes] On x86 and x86-64 systems with ELF binaries (especially Linux), due to a new optimization in GCC 5.x in combination with a recent version of GNU binutils, compiling Qt applications with -fPIE is no longer enough. Applications now need to be compiled with the -fPIC option if Qt's option "reduce relocations" is active. Note that Clang is known to generate incompatible code even with -fPIC if the -flto option is active. Task-number: QTBUG-45755 Change-Id: I66a35ce5f88941f29aa6ffff13dd210e0aa2728f Reviewed-by: Dmitry Shachnev <[email protected]> Reviewed-by: Simon Hausmann <[email protected]>
Someguynamedpie · May 13, 2015 · 3eca75d · 3eca75d
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diff --git a/dist/changes-5.4.2 b/dist/changes-5.4.2
@@ -34,6 +34,13 @@ information about a particular change.
   common EXIF-format (big-endian) was not working until 5.4.1. 5.4.2 restores the
   behavior of 5.4.0 and earlier for most EXIF-tagged JPEGs.
   EXIF orientation will be an opt-in starting with Qt 5.5.
+- On x86 and x86-64 systems with ELF binaries (especially Linux), due to
+  a new optimization in GCC 5.x in combination with a recent version of
+  GNU binutils, compiling Qt applications with -fPIE is no longer
+  enough. Applications now need to be compiled with the -fPIC option if
+  Qt's option "reduce relocations" is active. Note that Clang is known
+  to generate incompatible code even with -fPIC if the -flto option is
+  active.
 
 ****************************************************************************
 *                               Library                                    *

diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
@@ -1047,9 +1047,9 @@ Q_CORE_EXPORT int qrand();
 #  define QT_NO_SHAREDMEMORY
 #endif
 
-#if !defined(QT_BOOTSTRAPPED) && defined(QT_REDUCE_RELOCATIONS) && defined(__ELF__) && !defined(__PIC__)
+#if !defined(QT_BOOTSTRAPPED) && defined(QT_REDUCE_RELOCATIONS) && defined(__ELF__) && (!defined(__PIC__) || defined(__PIE__))
 #  error "You must build your code with position independent code if Qt was built with -reduce-relocations. "\
-         "Compile your code with -fPIC."
+         "Compile your code with -fPIC (-fPIE is not enough)."
 #endif
 
 namespace QtPrivate {