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

We claim in a couple places that the zeroth element of the module list
for a target is the main executable, but we don't actually enforce that
in the ModuleList class. As we saw, for instance, in

32dd5b20973bde1ef77fa3b84b9f85788a1a303a

it's not all that hard to get this to be off. This patch ensures that
the first object file of type Executable added to it is moved to the
front of the ModuleList. I also added a test for this.

In the normal course of operation, where the executable is added first,
this only adds a check for whether the first element in the module list
is an executable. If that's true, we just append as normal.

Note, the code in Target::GetExecutableModule doesn't actually agree
that the zeroth element must be the executable, it instead returns the
first Module of type Executable. But I can't tell whether that was a
change in intention or just working around the bug that we don't always
maintain this ordering. But given we've said this in scripting as well
as internally, I think we shouldn't change our minds about this.

1 files changed, 50 insertions, 0 deletions

diff --git a/lldb/test/API/functionalities/executable_first/TestExecutableFirst.py b/lldb/test/API/functionalities/executable_first/TestExecutableFirst.py
new file mode 100644
index 000000000000..5c5573d5b383
--- /dev/null
+++ b/lldb/test/API/functionalities/executable_first/TestExecutableFirst.py
@@ -0,0 +1,50 @@
+# 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
+
+    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")
+        )
+
+        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")