[-gmodules] Let LLDB log a warning if the Clang module hash mismatches.

This feature is mostly there to aid debugging of Clang module issues,
since the only useful actual the end-user can to is to recompile their
program.

Differential Revision: https://reviews.llvm.org/D70272

2 files changed, 70 insertions, 12 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index 5b508181406..08dcfa57ffe 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -1555,6 +1555,40 @@ SymbolFileDWARF::GetDIE(const DIERef &die_ref) {
     return DWARFDIE();
 }
 
+/// Return the DW_AT_(GNU_)dwo_name.
+static const char *GetDWOName(DWARFCompileUnit &dwarf_cu,
+                              const DWARFDebugInfoEntry &cu_die) {
+  const char *dwo_name =
+      cu_die.GetAttributeValueAsString(&dwarf_cu, DW_AT_GNU_dwo_name, nullptr);
+  if (!dwo_name)
+    dwo_name =
+        cu_die.GetAttributeValueAsString(&dwarf_cu, DW_AT_dwo_name, nullptr);
+  return dwo_name;
+}
+
+/// Return the DW_AT_(GNU_)dwo_id.
+/// FIXME: Technically 0 is a valid hash.
+static uint64_t GetDWOId(DWARFCompileUnit &dwarf_cu,
+                         const DWARFDebugInfoEntry &cu_die) {
+  uint64_t dwo_id =
+      cu_die.GetAttributeValueAsUnsigned(&dwarf_cu, DW_AT_GNU_dwo_id, 0);
+  if (!dwo_id)
+    dwo_id = cu_die.GetAttributeValueAsUnsigned(&dwarf_cu, DW_AT_dwo_id, 0);
+  return dwo_id;
+}
+
+llvm::Optional<uint64_t> SymbolFileDWARF::GetDWOId() {
+  if (GetNumCompileUnits() == 1) {
+    if (auto comp_unit = GetCompileUnitAtIndex(0))
+      if (DWARFCompileUnit *cu = llvm::dyn_cast_or_null<DWARFCompileUnit>(
+              GetDWARFCompileUnit(comp_unit.get())))
+        if (DWARFDebugInfoEntry *cu_die = cu->DIE().GetDIE())
+          if (uint64_t dwo_id = ::GetDWOId(*cu, *cu_die))
+            return dwo_id;
+  }
+  return {};
+}
+
 std::unique_ptr<SymbolFileDWARFDwo>
 SymbolFileDWARF::GetDwoSymbolFileForCompileUnit(
     DWARFUnit &unit, const DWARFDebugInfoEntry &cu_die) {
@@ -1571,15 +1605,13 @@ SymbolFileDWARF::GetDwoSymbolFileForCompileUnit(
   if (!dwarf_cu)
     return nullptr;
 
-  const char *dwo_name =
-      cu_die.GetAttributeValueAsString(dwarf_cu, DW_AT_GNU_dwo_name, nullptr);
+  const char *dwo_name = GetDWOName(*dwarf_cu, cu_die);
   if (!dwo_name)
     return nullptr;
 
   SymbolFileDWARFDwp *dwp_symfile = GetDwpSymbolFile();
   if (dwp_symfile) {
-    uint64_t dwo_id =
-        cu_die.GetAttributeValueAsUnsigned(dwarf_cu, DW_AT_GNU_dwo_id, 0);
+    uint64_t dwo_id = ::GetDWOId(*dwarf_cu, cu_die);
     std::unique_ptr<SymbolFileDWARFDwo> dwo_symfile =
         dwp_symfile->GetSymbolFileForDwoId(*dwarf_cu, dwo_id);
     if (dwo_symfile)
@@ -1619,15 +1651,18 @@ void SymbolFileDWARF::UpdateExternalModuleListIfNeeded() {
   if (m_fetched_external_modules)
     return;
   m_fetched_external_modules = true;
-
   DWARFDebugInfo *debug_info = DebugInfo();
 
   // Follow DWO skeleton unit breadcrumbs.
   const uint32_t num_compile_units = GetNumCompileUnits();
   for (uint32_t cu_idx = 0; cu_idx < num_compile_units; ++cu_idx) {
-    DWARFUnit *dwarf_cu = debug_info->GetUnitAtIndex(cu_idx);
+    auto *dwarf_cu =
+        llvm::dyn_cast<DWARFCompileUnit>(debug_info->GetUnitAtIndex(cu_idx));
+    if (!dwarf_cu)
+      continue;
+
     const DWARFBaseDIE die = dwarf_cu->GetUnitDIEOnly();
-    if (!die || die.HasChildren())
+    if (!die || die.HasChildren() || !die.GetDIE())
       continue;
 
     const char *name = die.GetAttributeValueAsString(DW_AT_name, nullptr);
@@ -1639,10 +1674,7 @@ void SymbolFileDWARF::UpdateExternalModuleListIfNeeded() {
     if (module_sp)
       continue;
 
-    const char *dwo_path =
-        die.GetAttributeValueAsString(DW_AT_GNU_dwo_name, nullptr);
-    if (!dwo_path)
-      dwo_path = die.GetAttributeValueAsString(DW_AT_dwo_name, nullptr);
+    const char *dwo_path = GetDWOName(*dwarf_cu, *die.GetDIE());
     if (!dwo_path)
       continue;
 
@@ -1685,12 +1717,35 @@ void SymbolFileDWARF::UpdateExternalModuleListIfNeeded() {
       GetObjectFile()->GetModule()->ReportWarning(
           "0x%8.8x: unable to locate module needed for external types: "
           "%s\nerror: %s\nDebugging will be degraded due to missing "
-          "types. Rebuilding your project will regenerate the needed "
+          "types. Rebuilding the project will regenerate the needed "
           "module files.",
           die.GetOffset(), dwo_module_spec.GetFileSpec().GetPath().c_str(),
           error.AsCString("unknown error"));
       continue;
     }
+
+    // Verify the DWO hash.
+    // FIXME: Technically "0" is a valid hash.
+    uint64_t dwo_id = ::GetDWOId(*dwarf_cu, *die.GetDIE());
+    if (!dwo_id)
+      continue;
+
+    auto *dwo_symfile =
+        llvm::dyn_cast_or_null<SymbolFileDWARF>(module_sp->GetSymbolFile());
+    if (!dwo_symfile)
+      continue;
+    llvm::Optional<uint64_t> dwo_dwo_id = dwo_symfile->GetDWOId();
+    if (!dwo_dwo_id)
+      continue;
+
+    if (dwo_id != dwo_dwo_id) {
+      GetObjectFile()->GetModule()->ReportWarning(
+          "0x%8.8x: Module %s is out-of-date (hash mismatch). Type information "
+          "from this module may be incomplete or inconsistent with the rest of "
+          "the program. Rebuilding the project will regenerate the needed "
+          "module files.",
+          die.GetOffset(), dwo_module_spec.GetFileSpec().GetPath().c_str());
+    }
   }
 }
 
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
index 1b8633ad1f1..a86350844ef 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h
@@ -300,6 +300,9 @@ public:
 
   virtual llvm::Optional<uint32_t> GetDwoNum() { return llvm::None; }
 
+  /// If this is a DWARF object with a single CU, return its DW_AT_dwo_id.
+  llvm::Optional<uint64_t> GetDWOId();
+
   static bool
   DIEInDeclContext(const lldb_private::CompilerDeclContext *parent_decl_ctx,
                    const DWARFDIE &die);