Do not resolve symbols from executables compiled with -fPIE.

Executables that are compiled with fPIE means they are compiled in a position
independent manner and are almost indistinguishable from the shared objects. A
reasonably reliable way to find if this was a `pie executable` is to check the
`DF_1_PIE` in the dynamic section of ELF.

The pseudo-code is:
```
if DT_FLAGS_1 dynamic section entry is present
  if DF_1_PIE is set in DT_FLAGS_1:
    print pie executable
  else
    print shared object
```

See https://stackoverflow.com/questions/34519521/why-does-gcc-create-a-shared-object-instead-of-an-executable-binary-according-to/34522357#34522357

Fixes root-project/root#7366

Patch by Alexander Penev (@alexander-penev)

lib/Interpreter/DynamicLibraryManagerSymbol.cpp

@@ -590,11 +590,14 @@ namespace cling {
   void HandleDynTab(const ELFFile<ELFT>* Elf, llvm::StringRef FileName,
                     llvm::SmallVector<llvm::StringRef,2>& RPath,
                     llvm::SmallVector<llvm::StringRef,2>& RunPath,
-                    std::vector<StringRef>& Deps) {
+                    std::vector<StringRef>& Deps,
+                    bool& isPIEExecutable) {
     const char *Data = "";
     if (Expected<StringRef> StrTabOrErr = getDynamicStrTab(Elf))
       Data = StrTabOrErr.get().data();
 
+    isPIEExecutable = false;
+
     auto DynamicEntriesOrError = Elf->dynamicEntries();
     if (!DynamicEntriesOrError) {
        cling::errs() << "Dyld: failed to read dynamic entries in"
@@ -613,6 +616,11 @@ namespace cling {
         case ELF::DT_RUNPATH:
           SplitPaths(Data + Dyn.d_un.d_val, RunPath, utils::kAllowNonExistant, platform::kEnvDelim, false);
           break;
+        case ELF::DT_FLAGS_1:
+          // Check if this is not a pie executable.
+          if (Dyn.d_un.d_val & llvm::ELF::DF_1_PIE)
+            isPIEExecutable = true;
+          break;
         // (Dyn.d_tag == ELF::DT_NULL) continue;
         // (Dyn.d_tag == ELF::DT_AUXILIARY || Dyn.d_tag == ELF::DT_FILTER)
       }
@@ -731,15 +739,28 @@ namespace cling {
           }
           llvm::object::ObjectFile *BinObjF = ObjFileOrErr.get().getBinary();
           if (BinObjF->isELF()) {
+            bool isPIEExecutable = false;
+
             if (const auto* ELF = dyn_cast<ELF32LEObjectFile>(BinObjF))
-              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps);
+              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps,
+                           isPIEExecutable);
             else if (const auto* ELF = dyn_cast<ELF32BEObjectFile>(BinObjF))
-              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps);
+              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps,
+                           isPIEExecutable);
             else if (const auto* ELF = dyn_cast<ELF64LEObjectFile>(BinObjF))
-              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps);
+              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps,
+                           isPIEExecutable);
             else if (const auto* ELF = dyn_cast<ELF64BEObjectFile>(BinObjF))
-              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps);
-
+              HandleDynTab(ELF->getELFFile(), FileName, RPath, RunPath, Deps,
+                           isPIEExecutable);
+
+            if ((level == 0) && isPIEExecutable) {
+              if (searchSystemLibraries)
+                m_SysLibraries.UnregisterLib(LibPath);
+              else
+                m_Libraries.UnregisterLib(LibPath);
+              return;
+            }
           } else if (BinObjF->isMachO()) {
             MachOObjectFile *Obj = (MachOObjectFile*)BinObjF;
             for (const auto &Command : Obj->load_commands()) {

test/DynamicLibraryManager/call_pie.c

@@ -0,0 +1,17 @@
+/*------------------------------------------------------------------------------
+// CLING - the C++ LLVM-based InterpreterG :)
+//
+// This file is dual-licensed: you can choose to license it under the University
+// of Illinois Open Source License or the GNU Lesser General Public License. See
+// LICENSE.TXT for details.
+//----------------------------------------------------------------------------*/
+
+// RUN: true
+// Used as executable/library source by pie.C, etc.
+CLING_EXPORT int cling_testlibrary_function() {
+  return 42;
+}
+
+int main() {
+  return 0;
+}

test/DynamicLibraryManager/pie.C

@@ -0,0 +1,39 @@
+//------------------------------------------------------------------------------
+// CLING - the C++ LLVM-based InterpreterG :)
+//
+// This file is dual-licensed: you can choose to license it under the University
+// of Illinois Open Source License or the GNU Lesser General Public License. See
+// LICENSE.TXT for details.
+//------------------------------------------------------------------------------
+
+// REQUIRES: not_system-windows
+
+// RUN: mkdir -p %t-dir/lib
+// RUN: %clang -shared -DCLING_EXPORT=%dllexport %S/call_lib_A.c -o%t-dir/lib/libcall_lib_A%shlibext
+// RUN: %clang -shared -DCLING_EXPORT=%dllexport %S/call_lib_B.c -o%t-dir/lib/libcall_lib_B%shlibext
+// RUN: %clang %fPIC -fpie -pie -DCLING_EXPORT=%dllexport %S/call_pie.c -o%t-dir/lib/call_pie_so%shlibext
+// RUN: %clang %fPIC -fpie -pie -DCLING_EXPORT=%dllexport %S/call_pie.c -o%t-dir/lib/call_pie
+// RUN: cat %s | LD_LIBRARY_PATH="%t-dir/lib" %cling 2>&1 | FileCheck %s
+
+// Test: Cling pragma for loading libraries. Lookup and load library Lib_L_AB
+//       that depends on two libraries Lib_A and Lib_B via file names.
+//       Lib_A and Lib_B are in LD_LIBRARY_PATH. Call_pie is "PIE" compiled excutable.
+//       Lookup functions from libraries and use them to print result value.
+//       We are expecting an error for the symbol from the PIE executable, which is
+//       expected not to be loaded by dynamic linker.
+
+#pragma cling load("libcall_lib_A")
+extern "C" int cling_testlibrary_function_A();
+cling_testlibrary_function_A()
+// CHECK: (int) 170
+
+#pragma cling load("libcall_lib_B")
+extern "C" int cling_testlibrary_function_B();
+cling_testlibrary_function_B()
+// CHECK: (int) 187
+
+extern "C" int cling_testlibrary_function();
+cling_testlibrary_function()
+// expected-error {{symbol 'cling_testlibrary_function' unresolved while linking}}
+
+//.q