Ensure that the executable module is ModuleList[0] (#78360)

lldb/source/Core/ModuleList.cpp

@@ -330,7 +330,29 @@ ModuleList::~ModuleList() = default;
 void ModuleList::AppendImpl(const ModuleSP &module_sp, bool use_notifier) {
   if (module_sp) {
     std::lock_guard<std::recursive_mutex> guard(m_modules_mutex);
-    m_modules.push_back(module_sp);
+    // We are required to keep the first element of the Module List as the
+    // executable module.  So check here and if the first module is NOT an 
+    // but the new one is, we insert this module at the beginning, rather than 
+    // at the end.
+    // We don't need to do any of this if the list is empty:
+    if (m_modules.empty()) {
+      m_modules.push_back(module_sp);
+    } else {
+      // Since producing the ObjectFile may take some work, first check the 0th
+      // element, and only if that's NOT an executable look at the incoming
+      // ObjectFile.  That way in the normal case we only look at the element
+      // 0 ObjectFile. 
+      const bool elem_zero_is_executable 
+          = m_modules[0]->GetObjectFile()->GetType() 
+              == ObjectFile::Type::eTypeExecutable;
+      lldb_private::ObjectFile *obj = module_sp->GetObjectFile();
+      if (!elem_zero_is_executable && obj 
+          && obj->GetType() == ObjectFile::Type::eTypeExecutable) {
+        m_modules.insert(m_modules.begin(), module_sp);
+      } else {
+        m_modules.push_back(module_sp);
+      }
+    }
     if (use_notifier && m_notifier)
       m_notifier->NotifyModuleAdded(*this, module_sp);
   }

lldb/test/API/functionalities/executable_first/Makefile

@@ -0,0 +1,4 @@
+CXX_SOURCES := main.cpp
+DYLIB_CXX_SOURCES := b.cpp
+DYLIB_NAME := bar
+include Makefile.rules

lldb/test/API/functionalities/executable_first/TestExecutableFirst.py

@@ -0,0 +1,54 @@
+# This test checks that we make the executable the first
+# element in the image list.
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestExecutableIsFirst(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    # ELF does not have a hard distinction between shared libraries and
+    # (position-independent) executables
+    @skipIf(oslist=no_match(lldbplatformutil.getDarwinOSTriples()+["windows"]))
+    def test_executable_is_first_before_run(self):
+        self.build()
+
+        ctx = self.platformContext
+        lib_name = ctx.shlib_prefix + "bar." + ctx.shlib_extension
+
+        exe = self.getBuildArtifact("a.out")
+        lib = self.getBuildArtifact(lib_name)
+
+        target = self.dbg.CreateTarget(None)
+        module = target.AddModule(lib, None, None)
+        self.assertTrue(module.IsValid(), "Added the module for the library")
+
+        module = target.AddModule(exe, None, None)
+        self.assertTrue(module.IsValid(), "Added the executable module")
+
+        # This is the executable module so it should be the first in the list:
+        first_module = target.GetModuleAtIndex(0)
+        print("This is the first test, this one succeeds")
+        self.assertEqual(module, first_module, "This executable is the first module")
+
+        # The executable property is an SBFileSpec to the executable.  Make sure
+        # that is also right:
+        executable_module = target.executable
+        self.assertEqual(
+            first_module.file, executable_module, "Python property is also our module"
+        )
+
+    def test_executable_is_first_during_run(self):
+        self.build()
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(
+            self, "break after function call", lldb.SBFileSpec("main.cpp"),
+            extra_images=["bar"]
+        )
+
+        first_module = target.GetModuleAtIndex(0)
+        self.assertTrue(first_module.IsValid(), "We have at least one module")
+        executable_module = target.executable
+        self.assertEqual(first_module.file, executable_module, "They are the same")

lldb/test/API/functionalities/executable_first/b.cpp

@@ -0,0 +1 @@
+int LLDB_DYLIB_EXPORT b_function() { return 500; }

lldb/test/API/functionalities/executable_first/main.cpp

@@ -0,0 +1,6 @@
+extern int b_function();
+
+int main(int argc, char* argv[]) {
+  int ret_value = b_function();
+  return ret_value; // break after function call
+}