[lldb][libc++] Hide all libc++ implementation details from stacktraces

This commit changes the libc++ frame recognizer to hide implementation
details of libc++ more aggressively. The applied heuristic is rather
straightforward: We consider every function name starting with `__` as
an implementation detail.

This works pretty neatly for `std::invoke`, `std::function`,
`std::sort`, `std::map::emplace` and many others. Also, this should
align quite nicely with libc++'s general coding convention of using the
`__` for their implementation details, thereby keeping the future
maintenance effort low.

However, it is noteworthy, that this does not work 100% in all cases:
E.g., for `std::ranges::sort`, itself is not really a function call, but
an object with an overloaded `operator()`, which means that there is no
actual call `std::ranges::sort` in the call stack.

Author: vogelsgesang

libcxx/docs/UserDocumentation.rst

@@ -343,6 +343,32 @@ Third-party Integrations
 
 Libc++ provides integration with a few third-party tools.
 
+Debugging libc++ internals in LLDB
+----------------------------------
+
+LLDB hides the implementation details of libc++ by default.
+
+E.g., when setting a breakpoint in a comparator passed to ``std::sort``, the
+backtrace will read as
+
+.. code-block::
+
+  (lldb) thread backtrace
+  * thread #1, name = 'a.out', stop reason = breakpoint 3.1
+    * frame #0: 0x000055555555520e a.out`my_comparator(a=1, b=8) at test-std-sort.cpp:6:3
+      frame #7: 0x0000555555555615 a.out`void std::__1::sort[abi:ne200000]<std::__1::__wrap_iter<int*>, bool (*)(int, int)>(__first=(item = 8), __last=(item = 0), __comp=(a.out`my_less(int, int) at test-std-sort.cpp:5)) at sort.h:1003:3
+      frame #8: 0x000055555555531a a.out`main at test-std-sort.cpp:24:3
+
+Note how the caller of ``my_comparator`` is shown as ``std::sort``. Looking at
+the frame numbers, we can see that frames #1 until #6 were hidden. Those frames
+represent internal implementation details such as ``__sort4`` and similar
+utility functions.
+
+To also show those implementation details, use ``thread backtrace -u``.
+Alternatively, to disable those compact backtraces for good, use
+``frame recognizer list`` and ``frame recognizer delete`` to delete the libc++
+frame recognizer.
+
 GDB Pretty printers for libc++
 ------------------------------
 

lldb/source/Plugins/LanguageRuntime/CPlusPlus/CPPLanguageRuntime.cpp

@@ -45,7 +45,7 @@ char CPPLanguageRuntime::ID = 0;
 /// A frame recognizer that is installed to hide libc++ implementation
 /// details from the backtrace.
 class LibCXXFrameRecognizer : public StackFrameRecognizer {
-  std::array<RegularExpression, 4> m_hidden_regex;
+  std::array<RegularExpression, 2> m_hidden_regex;
   RecognizedStackFrameSP m_hidden_frame;
 
   struct LibCXXHiddenFrame : public RecognizedStackFrame {
@@ -55,28 +55,17 @@ class LibCXXFrameRecognizer : public StackFrameRecognizer {
 public:
   LibCXXFrameRecognizer()
       : m_hidden_regex{
-            // internal implementation details of std::function
+            // internal implementation details in the `std::` namespace
             //    std::__1::__function::__alloc_func<void (*)(), std::__1::allocator<void (*)()>, void ()>::operator()[abi:ne200000]
             //    std::__1::__function::__func<void (*)(), std::__1::allocator<void (*)()>, void ()>::operator()
             //    std::__1::__function::__value_func<void ()>::operator()[abi:ne200000]() const
-            RegularExpression{""
-              R"(^std::__[^:]*::)" // Namespace.
-              R"(__function::.*::operator\(\))"},
-            // internal implementation details of std::function in ABI v2
             //    std::__2::__function::__policy_invoker<void (int, int)>::__call_impl[abi:ne200000]<std::__2::__function::__default_alloc_func<int (*)(int, int), int (int, int)>>
-            RegularExpression{""
-              R"(^std::__[^:]*::)" // Namespace.
-              R"(__function::.*::__call_impl)"},
-            // internal implementation details of std::invoke
-            //   std::__1::__invoke[abi:ne200000]<void (*&)()>
-            RegularExpression{
-              R"(^std::__[^:]*::)" // Namespace.
-              R"(__invoke)"},
-            // internal implementation details of std::invoke
-            //   std::__1::__invoke_void_return_wrapper<void, true>::__call[abi:ne200000]<void (*&)()>
-            RegularExpression{
-              R"(^std::__[^:]*::)" // Namespace.
-              R"(__invoke_void_return_wrapper<.*>::__call)"}
+            //    std::__1::__invoke[abi:ne200000]<void (*&)()>
+            //    std::__1::__invoke_void_return_wrapper<void, true>::__call[abi:ne200000]<void (*&)()>
+            RegularExpression{R"(^std::__[^:]*::__)"},
+            // internal implementation details in the `std::ranges` namespace
+            //    std::__1::ranges::__sort::__sort_fn_impl[abi:ne200000]<std::__1::__wrap_iter<int*>, std::__1::__wrap_iter<int*>, bool (*)(int, int), std::__1::identity>
+            RegularExpression{R"(^std::__[^:]*::ranges::__)"},
         },
         m_hidden_frame(new LibCXXHiddenFrame()) {}
 

lldb/test/API/lang/cpp/libcxx-internals-recognizer/Makefile

@@ -0,0 +1,5 @@
+CXX_SOURCES := main.cpp
+USE_LIBCPP := 1
+CXXFLAGS_EXTRAS := -std=c++20
+
+include Makefile.rules

lldb/test/API/lang/cpp/libcxx-internals-recognizer/TestLibcxxInternalsRecognizer.py

@@ -0,0 +1,56 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class LibCxxInternalsRecognizerTestCase(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    @add_test_categories(["libc++"])
+    def test_frame_recognizer(self):
+        """Test that implementation details of libc++ are hidden"""
+        self.build()
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(
+            self, "break here", lldb.SBFileSpec("main.cpp")
+        )
+
+        expected_parents = {
+            "sort_less(int, int)": ["::sort", "test_algorithms"],
+            # `std::ranges::sort` is implemented as an object of types `__sort`,
+            # which unfortunately means that there is no `std::ranges::sort`
+            # stack frame, and `main` is the direct parent of `my_less_ranges`.
+            "ranges_sort_less(int, int)": ["test_algorithms"],
+            # `ranges::views::transform` internally uses `std::invoke`, and that
+            # call also shows up in the stack trace
+            "view_transform(int)": ["::invoke", "ranges::transform_view", "test_algorithms"],
+            # Various types of `invoke` calls
+            "consume_number(int)": ["::invoke", "test_invoke"],
+            "invoke_add(int, int)": ["::invoke", "test_invoke"],
+            "Callable::member_function(int) const": ["::invoke", "test_invoke"],
+            "Callable::operator()(int) const": ["::invoke", "test_invoke"],
+            # Containers
+            "MyKey::operator<(MyKey const&) const": ["less", "::emplace", "test_containers"],
+        }
+        stop_set = set()
+        while process.GetState() != lldb.eStateExited:
+            fn = thread.GetFrameAtIndex(0).GetFunctionName()
+            stop_set.add(fn)
+            self.assertIn(fn, expected_parents.keys())
+            frame_id = 1
+            for expected_parent in expected_parents[fn]:
+                # Skip all hidden frames
+                while (
+                    frame_id < thread.GetNumFrames()
+                    and thread.GetFrameAtIndex(frame_id).IsHidden()
+                ):
+                    frame_id = frame_id + 1
+                # Expect the correct parent frame
+                self.assertIn(
+                    expected_parent, thread.GetFrameAtIndex(frame_id).GetFunctionName()
+                )
+                frame_id = frame_id + 1
+            process.Continue()
+
+        # Make sure that we actually verified all intended scenarios
+        self.assertEqual(len(stop_set), len(expected_parents))

lldb/test/API/lang/cpp/libcxx-internals-recognizer/main.cpp

@@ -0,0 +1,86 @@
+#include <algorithm>
+#include <functional>
+#include <map>
+#include <ranges>
+#include <vector>
+
+bool sort_less(int a, int b) {
+  __builtin_printf("break here");
+  return a < b;
+}
+
+bool ranges_sort_less(int a, int b) {
+  __builtin_printf("break here");
+  return a < b;
+}
+
+int view_transform(int a) {
+  __builtin_printf("break here");
+  return a * a;
+}
+
+void test_algorithms() {
+  std::vector<int> vec{8, 1, 3, 2};
+
+  // The internal frames for `std::sort` should be hidden
+  std::sort(vec.begin(), vec.end(), sort_less);
+
+  // The internal frames for `ranges::sort` should be hidden
+  std::ranges::sort(vec.begin(), vec.end(), ranges_sort_less);
+
+  // Same for views
+  for (auto x : vec | std::ranges::views::transform(view_transform)) {
+    // no-op
+  }
+}
+
+void consume_number(int i) { __builtin_printf("break here"); }
+
+int invoke_add(int i, int j) {
+  __builtin_printf("break here");
+  return i + j;
+}
+
+struct Callable {
+  Callable(int num) : num_(num) {}
+  void operator()(int i) const { __builtin_printf("break here"); }
+  void member_function(int i) const { __builtin_printf("break here"); }
+  int num_;
+};
+
+void test_invoke() {
+  // Invoke a void-returning function
+  std::invoke(consume_number, -9);
+
+  // Invoke a non-void-returning function
+  std::invoke(invoke_add, 1, 10);
+
+  // Invoke a member function
+  const Callable foo(314159);
+  std::invoke(&Callable::member_function, foo, 1);
+
+  // Invoke a function object
+  std::invoke(Callable(12), 18);
+}
+
+struct MyKey {
+  int x;
+  bool operator==(const MyKey &) const = default;
+  bool operator<(const MyKey &other) const {
+    __builtin_printf("break here");
+    return x < other.x;
+  }
+};
+
+void test_containers() {
+  std::map<MyKey, int> map;
+  map.emplace(MyKey{1}, 2);
+  map.emplace(MyKey{2}, 3);
+}
+
+int main() {
+  test_algorithms();
+  test_invoke();
+  test_containers();
+  return 0;
+}