Fix lldb-dap non-leaf frame source resolution issue

Author: Jeffrey Tan

lldb/tools/lldb-dap/DAP.cpp

@@ -657,18 +657,31 @@ std::optional<protocol::Source> DAP::ResolveSource(const lldb::SBFrame &frame) {
   if (!frame.IsValid())
     return std::nullopt;
 
-  const lldb::SBAddress frame_pc = frame.GetPCAddress();
-  if (DisplayAssemblySource(debugger, frame_pc))
+  // IMPORTANT: Get line entry from symbol context, NOT from PC address.
+  // When a frame's PC points to a return address (the instruction
+  // after a call), that address may have line number 0 for compiler generated
+  // code.
+  //
+  // EXAMPLE: If PC is at 0x1004 (frame return address after the call
+  // instruction) with no line info, but 0x1003 (in the middle of previous call
+  // instruction) is at line 42, symbol context returns line 42.
+  //
+  // NOTE: This issue is non-deterministic and depends on compiler debug info
+  // generation, making it difficult to create a reliable automated test.
+  const lldb::SBLineEntry frame_line_entry = frame.GetLineEntry();
+  if (DisplayAssemblySource(debugger, frame_line_entry)) {
+    const lldb::SBAddress frame_pc = frame.GetPCAddress();
     return ResolveAssemblySource(frame_pc);
+  }
 
-  return CreateSource(frame.GetLineEntry().GetFileSpec());
+  return CreateSource(frame_line_entry.GetFileSpec());
 }
 
 std::optional<protocol::Source> DAP::ResolveSource(lldb::SBAddress address) {
-  if (DisplayAssemblySource(debugger, address))
+  lldb::SBLineEntry line_entry = GetLineEntryForAddress(target, address);
+  if (DisplayAssemblySource(debugger, line_entry))
     return ResolveAssemblySource(address);
 
-  lldb::SBLineEntry line_entry = GetLineEntryForAddress(target, address);
   if (!line_entry.IsValid())
     return std::nullopt;
 

lldb/tools/lldb-dap/ProtocolUtils.cpp

@@ -27,7 +27,7 @@ using namespace lldb_dap::protocol;
 namespace lldb_dap {
 
 static bool ShouldDisplayAssemblySource(
-    lldb::SBAddress address,
+    lldb::SBLineEntry line_entry,
     lldb::StopDisassemblyType stop_disassembly_display) {
   if (stop_disassembly_display == lldb::eStopDisassemblyTypeNever)
     return false;
@@ -37,7 +37,6 @@ static bool ShouldDisplayAssemblySource(
 
   // A line entry of 0 indicates the line is compiler generated i.e. no source
   // file is associated with the frame.
-  auto line_entry = address.GetLineEntry();
   auto file_spec = line_entry.GetFileSpec();
   if (!file_spec.IsValid() || line_entry.GetLine() == 0 ||
       line_entry.GetLine() == LLDB_INVALID_LINE_NUMBER)
@@ -174,10 +173,10 @@ bool IsAssemblySource(const protocol::Source &source) {
 }
 
 bool DisplayAssemblySource(lldb::SBDebugger &debugger,
-                           lldb::SBAddress address) {
+                           lldb::SBLineEntry line_entry) {
   const lldb::StopDisassemblyType stop_disassembly_display =
       GetStopDisassemblyDisplay(debugger);
-  return ShouldDisplayAssemblySource(address, stop_disassembly_display);
+  return ShouldDisplayAssemblySource(line_entry, stop_disassembly_display);
 }
 
 std::string GetLoadAddressString(const lldb::addr_t addr) {

lldb/tools/lldb-dap/ProtocolUtils.h

@@ -53,7 +53,8 @@ std::optional<protocol::Source> CreateSource(const lldb::SBFileSpec &file);
 /// Checks if the given source is for assembly code.
 bool IsAssemblySource(const protocol::Source &source);
 
-bool DisplayAssemblySource(lldb::SBDebugger &debugger, lldb::SBAddress address);
+bool DisplayAssemblySource(lldb::SBDebugger &debugger,
+                           lldb::SBLineEntry line_entry);
 
 /// Get the address as a 16-digit hex string, e.g. "0x0000000000012345"
 std::string GetLoadAddressString(const lldb::addr_t addr);