QPlugin: don't use QFile::read() if map() fails on Unix

If we can't mmap(), then libdl won't be able to either.

Change-Id: I42eb903a916645db9900fffd16a492a1ac25903f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
(cherry picked from commit 0be5bf3e64cee329249c1174590d6a0c1a7a543f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 15 insertions, 2 deletions

diff --git a/src/corelib/plugin/qlibrary.cpp b/src/corelib/plugin/qlibrary.cpp
index a10b3db1a2..2ec32bc43b 100644
--- a/src/corelib/plugin/qlibrary.cpp
+++ b/src/corelib/plugin/qlibrary.cpp
@@ -252,16 +252,29 @@ static bool findPatternUnloaded(const QString &library, QLibraryPrivate *lib)
     constexpr qint64 MaxMemoryMapSize =
             Q_INT64_C(1) << (sizeof(qsizetype) > 4 ? 40 : 29);
 
-    QByteArray data;
     qsizetype fdlen = qMin(file.size(), MaxMemoryMapSize);
     const char *filedata = reinterpret_cast<char *>(file.map(0, fdlen));
 
+#ifdef Q_OS_UNIX
     if (filedata == nullptr) {
-        // Try reading the data into memory instead (up to 64 MB).
+        // If we can't mmap(), then the dynamic loader won't be able to either.
+        // This can't be used as a plugin.
+        if (qt_debug_component())
+            qWarning("%s: failed to map to memory: %ls", QFile::encodeName(library).constData(),
+                     qUtf16Printable(file.errorString()));
+        return false;
+    }
+#else
+    QByteArray data;
+    if (filedata == nullptr) {
+        // It's unknown at this point whether Windows supports LoadLibrary() on
+        // files that fail to CreateFileMapping / MapViewOfFile, so we err on
+        // the side of doing a regular read into memory (up to 64 MB).
         data = file.read(64 * 1024 * 1024);
         filedata = data.constData();
         fdlen = data.size();
     }
+#endif
 
     /*
        ELF and Mach-O binaries with GCC have .qplugin sections.