[Lldb-commits] [lldb] [lldb][test] Fix TestEmptyFuncThreadStepOut.py (PR #161788)

[Igor Kudrin via lldb-commits]

https://github.com/igorkudrin updated https://github.com/llvm/llvm-project/pull/161788

>From def07ea0df5cefe227955f6cdaae2c668dc84f0f Mon Sep 17 00:00:00 2001
From: Igor Kudrin <ikudrin at accesssoftek.com>
Date: Thu, 2 Oct 2025 22:42:06 -0700
Subject: [PATCH 1/2] [lldb][test] Fix TestEmptyFuncThreadStepOut.py

The test did not work as intended when the empty function 'done()'
contained epilog code, because a breakpoint was set on the first
instruction of the epilog instead of on the last instruction of the
function. This caused the test to pass even with the fix from #126838
reverted.
---
 .../TestEmptyFuncThreadStepOut.py             | 20 +++++++++++++++----
 .../thread/finish-from-empty-func/main.c      |  1 +
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py b/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py
index f5d3da530f4f5..be0d47d1d8fe6 100644
--- a/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py
+++ b/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py
@@ -15,10 +15,23 @@ class FinishFromEmptyFunctionTestCase(TestBase):
     def test_finish_from_empty_function(self):
         """Test that when stopped at a breakpoint in an empty function, finish leaves it correctly."""
         self.build()
-        exe = self.getBuildArtifact("a.out")
-        target, process, thread, _ = lldbutil.run_to_name_breakpoint(
-            self, "done", exe_name=exe
+        target, _, thread, _ = lldbutil.run_to_source_breakpoint(
+            self, "// Set breakpoint here", lldb.SBFileSpec("main.c")
         )
+        # Find the last instruction address of 'done()' and set a breakpoint there.
+        error = lldb.SBError()
+        ret_bp_addr = lldb.SBAddress()
+        while True:
+            thread.StepInstruction(False, error)
+            self.assertTrue(error.Success())
+            frame = thread.GetSelectedFrame()
+            if "done" in frame.GetFunctionName():
+                ret_bp_addr = frame.GetPCAddress()
+            elif ret_bp_addr.IsValid():
+                break
+        ret_bp = target.BreakpointCreateByAddress(ret_bp_addr.GetLoadAddress(target))
+        self.assertTrue(ret_bp.IsValid())
+        self.runCmd("cont")
         if self.TraceOn():
             self.runCmd("bt")
 
@@ -29,7 +42,6 @@ def test_finish_from_empty_function(self):
         )
         self.assertTrue(safety_bp.IsValid())
 
-        error = lldb.SBError()
         thread.StepOut(error)
         self.assertTrue(error.Success())
 
diff --git a/lldb/test/API/functionalities/thread/finish-from-empty-func/main.c b/lldb/test/API/functionalities/thread/finish-from-empty-func/main.c
index bc66a548a89df..b3f90db5e2562 100644
--- a/lldb/test/API/functionalities/thread/finish-from-empty-func/main.c
+++ b/lldb/test/API/functionalities/thread/finish-from-empty-func/main.c
@@ -2,6 +2,7 @@
 void done() {}
 int main() {
   puts("in main");
+  done(); // Set breakpoint here
   done();
   puts("leaving main");
   return 0;

>From 5ff7d663500d40a29b9988aa069784653f718178 Mon Sep 17 00:00:00 2001
From: Igor Kudrin <ikudrin at accesssoftek.com>
Date: Thu, 16 Oct 2025 23:54:30 -0700
Subject: [PATCH 2/2] fixup! Add comments to the test

---
 .../TestEmptyFuncThreadStepOut.py                      | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py b/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py
index be0d47d1d8fe6..c95a57ff55815 100644
--- a/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py
+++ b/lldb/test/API/functionalities/thread/finish-from-empty-func/TestEmptyFuncThreadStepOut.py
@@ -13,12 +13,15 @@ class FinishFromEmptyFunctionTestCase(TestBase):
 
     @skipIf(compiler="clang", compiler_version=['<', '17.0'])
     def test_finish_from_empty_function(self):
-        """Test that when stopped at a breakpoint in an empty function, finish leaves it correctly."""
+        """Test that when stopped at a breakpoint located at the last instruction
+        of a function, finish leaves it correctly."""
         self.build()
         target, _, thread, _ = lldbutil.run_to_source_breakpoint(
             self, "// Set breakpoint here", lldb.SBFileSpec("main.c")
         )
-        # Find the last instruction address of 'done()' and set a breakpoint there.
+        # Find the address of the last instruction of 'done()' and set a breakpoint there.
+        # Even though 'done()' is empty, it may contain prologue and epilogue code, so
+        # simply setting a breakpoint at the function can place it before 'ret'.
         error = lldb.SBError()
         ret_bp_addr = lldb.SBAddress()
         while True:
@@ -28,9 +31,12 @@ def test_finish_from_empty_function(self):
             if "done" in frame.GetFunctionName():
                 ret_bp_addr = frame.GetPCAddress()
             elif ret_bp_addr.IsValid():
+                # The entire function 'done()' has been stepped through, so 'ret_bp_addr'
+                # now contains the address of its last instruction, i.e. 'ret'.
                 break
         ret_bp = target.BreakpointCreateByAddress(ret_bp_addr.GetLoadAddress(target))
         self.assertTrue(ret_bp.IsValid())
+        # Resume the execution and hit the new breakpoint.
         self.runCmd("cont")
         if self.TraceOn():
             self.runCmd("bt")