[lldb] Warn when we fail to find dwo/dwp files

[labath]

Summary

This ensures that the user is aware that many commands will not work
correctly.

We print the warning only once (per module) to avoid spamming the user
with potentially thousands of error messages.

[JDevlieghere]

LGTM.

FWIW I'm planning some changes to the error reporting "soonish". The gist is using error/warning events which Xcode (or VSCode) can subscribe to. I'll send out an RFC with more details as I get closer to working on this.

[labath]

This code can be invoked concurrently (during indexing). Use atomic test-and-set
to ensure correctness.

[JDevlieghere]

Might a llvm::once_flag + llvm::call_once be simpler?

[labath]

In D120892#3357424, @JDevlieghere wrote:

FWIW I'm planning some changes to the error reporting "soonish". The gist is using error/warning events which Xcode (or VSCode) can subscribe to. I'll send out an RFC with more details as I get closer to working on this.

Sounds like a good idea.

[labath]

In D120892#3357780, @JDevlieghere wrote:

Might a llvm::once_flag + llvm::call_once be simpler?

Simpler... maybe.. depends how you look at it.

But, synchronization-wise, it is overkill. once_flag ensures that none of the racing threads can make progress until the action terminates. Most of the time, that's exactly what we want, but here the correct operation of the other threads is not affected by this action, so it is sufficient that the warning gets printed "eventually".

[JDevlieghere]

Cool, thanks for the explanation. Ship it.

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h

protected:
 
   typedef std::unordered_map<lldb::offset_t, lldb_private::DebugMacrosSP>
       DebugMacrosMap;
   DebugMacrosMap m_debug_macros_map;
 
   ExternalTypeModuleMap m_external_type_modules;
   std::unique_ptr<lldb_private::DWARFIndex> m_index;
   bool m_fetched_external_modules : 1;
+  bool m_dwo_warning_issued : 1;
   lldb_private::LazyBool m_supports_DW_AT_APPLE_objc_complete_type;
 
   typedef std::set<DIERef> DIERefSet;
   typedef llvm::StringMap<DIERefSet> NameToOffsetMap;
   NameToOffsetMap m_function_scope_qualified_name_map;
   std::unique_ptr<DWARFDebugRanges> m_ranges;
   UniqueDWARFASTTypeMap m_unique_ast_type_map;
   DIEToTypePtr m_die_to_type;

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

 SymbolFileDWARF::SymbolFileDWARF(ObjectFileSP objfile_sp,
                                  SectionList *dwo_section_list)
     : SymbolFile(std::move(objfile_sp)),
       UserID(0x7fffffff00000000), // Used by SymbolFileDWARFDebugMap to
                                   // when this class parses .o files to
                                   // contain the .o file index/ID
       m_debug_map_module_wp(), m_debug_map_symfile(nullptr),
       m_context(m_objfile_sp->GetModule()->GetSectionList(), dwo_section_list),
-      m_fetched_external_modules(false),
+      m_fetched_external_modules(false), m_dwo_warning_issued(false),
       m_supports_DW_AT_APPLE_objc_complete_type(eLazyBoolCalculate) {}
 
 SymbolFileDWARF::~SymbolFileDWARF() = default;
 
 static ConstString GetDWARFMachOSegmentName() {
   static ConstString g_dwarf_section_name("__DWARF");
   return g_dwarf_section_name;
 }
if (dwo_file.IsRelative()) {
       // launched.
       dwo_file.PrependPathComponent(
           m_objfile_sp->GetFileSpec().GetDirectory().GetStringRef());
     }
     FileSystem::Instance().Resolve(dwo_file);
     dwo_file.AppendPathComponent(dwo_name);
   }
 
-  if (!FileSystem::Instance().Exists(dwo_file))
+  if (!FileSystem::Instance().Exists(dwo_file)) {
+    if (!m_dwo_warning_issued) {
+      m_dwo_warning_issued = true;
+      GetObjectFile()->GetModule()->ReportWarning(
+          "unable to locate separate debug file (dwo, dwp). Debugging will be "
+          "degraded.");
+    }
     return nullptr;
+  }
 
   const lldb::offset_t file_offset = 0;
   DataBufferSP dwo_file_data_sp;
   lldb::offset_t dwo_file_data_offset = 0;
   ObjectFileSP dwo_obj_file = ObjectFile::FindPlugin(
       GetObjectFile()->GetModule(), &dwo_file, file_offset,
       FileSystem::Instance().GetByteSize(dwo_file), dwo_file_data_sp,
       dwo_file_data_offset);

lldb/test/Shell/SymbolFile/DWARF/x86/dwo-not-found-warning.cpp

+// RUN: %clang --target=x86_64-pc-linux -g -gsplit-dwarf -c %s -o %t.o
+// RUN: rm %t.dwo
+// RUN: %lldb %t.o -o "br set -n main" -o exit 2>&1 | FileCheck %s
+
+// CHECK: warning: {{.*}} unable to locate separate debug file (dwo, dwp). Debugging will be degraded.
+
+int main() { return 47; }