[Lldb-commits] [lldb] a57b62d - [lldb] Fix thread step until to not set breakpoint(s) on incorrect line numbers

[Venkata Ramanaiah Nalamothu via lldb-commits]

Author: Venkata Ramanaiah Nalamothu
Date: 2022-06-25T00:01:04+05:30
New Revision: a57b62deef37c7f2ec31bca3bf9173a6206bfb9b

URL: https://github.com/llvm/llvm-project/commit/a57b62deef37c7f2ec31bca3bf9173a6206bfb9b
DIFF: https://github.com/llvm/llvm-project/commit/a57b62deef37c7f2ec31bca3bf9173a6206bfb9b.diff

LOG: [lldb] Fix thread step until to not set breakpoint(s) on incorrect line numbers

The requirements for "thread until <line number>" are:

a) If any code contributed by <line number> or the nearest subsequent of <line number> is executed before leaving the function, stop
b) If you end up leaving the function w/o triggering (a), then stop

In case of (a), since the <line number> may have multiple entries in the line table and the compiler might have scheduled/moved the relevant code across, and the lldb does not know the control flow, set breakpoints on all the line table entries of best match of <line number> i.e. exact or the nearest subsequent line.

Along with the above, currently, CommandObjectThreadUntil is also setting the breakpoints on all the subsequent line numbers after the best match and this latter part is wrong.

This issue is discussed at http://lists.llvm.org/pipermail/lldb-dev/2018-August/013979.html.

In fact, currently `TestStepUntil.py` is not actually testing step until scenarios and `test_missing_one` test fails without this patch if tests are made to run. Fixed the test as well.

Reviewed By: jingham

Differential Revision: https://reviews.llvm.org/D50304

Added: 
    

Modified: 
    lldb/source/Commands/CommandObjectThread.cpp
    lldb/test/API/functionalities/thread/step_until/TestStepUntil.py

Removed: 
    


################################################################################
diff  --git a/lldb/source/Commands/CommandObjectThread.cpp b/lldb/source/Commands/CommandObjectThread.cpp
index 037bbafdf8940..9396c36154979 100644
--- a/lldb/source/Commands/CommandObjectThread.cpp
+++ b/lldb/source/Commands/CommandObjectThread.cpp
@@ -1033,11 +1033,21 @@ class CommandObjectThreadUntil : public CommandObjectParsed {
         line_table->FindLineEntryByAddress(fun_end_addr, function_start,
                                            &end_ptr);
 
+        // Since not all source lines will contribute code, check if we are
+        // setting the breakpoint on the exact line number or the nearest
+        // subsequent line number and set breakpoints at all the line table
+        // entries of the chosen line number (exact or nearest subsequent).
         for (uint32_t line_number : line_numbers) {
+          LineEntry line_entry;
+          bool exact = false;
           uint32_t start_idx_ptr = index_ptr;
+          start_idx_ptr = sc.comp_unit->FindLineEntry(
+              index_ptr, line_number, nullptr, exact, &line_entry);
+          if (start_idx_ptr != UINT32_MAX)
+            line_number = line_entry.line;
+          exact = true;
+          start_idx_ptr = index_ptr;
           while (start_idx_ptr <= end_ptr) {
-            LineEntry line_entry;
-            const bool exact = false;
             start_idx_ptr = sc.comp_unit->FindLineEntry(
                 start_idx_ptr, line_number, nullptr, exact, &line_entry);
             if (start_idx_ptr == UINT32_MAX)

diff  --git a/lldb/test/API/functionalities/thread/step_until/TestStepUntil.py b/lldb/test/API/functionalities/thread/step_until/TestStepUntil.py
index 0145b34f31de5..ee25d1343735f 100644
--- a/lldb/test/API/functionalities/thread/step_until/TestStepUntil.py
+++ b/lldb/test/API/functionalities/thread/step_until/TestStepUntil.py
@@ -19,7 +19,7 @@ def setUp(self):
         self.greater_than_two = line_number('main.c', 'Greater than or equal to 2.')
         self.back_out_in_main = line_number('main.c', 'Back out in main')
 
-    def do_until (self, args, until_lines, expected_linenum):
+    def common_setup (self, args):
         self.build()
         exe = self.getBuildArtifact("a.out")
 
@@ -48,7 +48,8 @@ def do_until (self, args, until_lines, expected_linenum):
         thread = threads[0]
         return thread
 
-        thread = self.common_setup(None)
+    def do_until (self, args, until_lines, expected_linenum):
+        thread = self.common_setup(args)
 
         cmd_interp = self.dbg.GetCommandInterpreter()
         ret_obj = lldb.SBCommandReturnObject()
@@ -77,7 +78,7 @@ def test_targetting_two_hitting_second (self):
         self.do_until(None, [self.less_than_two, self.greater_than_two], self.less_than_two)
 
     def test_missing_one (self):
-        """Test thread step until - targeting one line and missing it."""
+        """Test thread step until - targeting one line and missing it by stepping out to call site"""
         self.do_until(["foo", "bar", "baz"], [self.less_than_two], self.back_out_in_main)