[lldb] Print a warning on checksum mismatch (#107968)

Print a warning when the debugger detects a mismatch between the MD5
checksum in the DWARF 5 line table and the file on disk. The warning is
printed only once per file.

Author: JDevlieghere

lldb/include/lldb/Core/SourceManager.h

@@ -74,6 +74,10 @@ class SourceManager {
 
     const Checksum &GetChecksum() const { return m_checksum; }
 
+    llvm::once_flag &GetChecksumWarningOnceFlag() {
+      return m_checksum_warning_once_flag;
+    }
+
   protected:
     /// Set file and update modification time.
     void SetSupportFile(lldb::SupportFileSP support_file_sp);
@@ -87,6 +91,9 @@ class SourceManager {
     /// Keep track of the on-disk checksum.
     Checksum m_checksum;
 
+    /// Once flag for emitting a checksum mismatch warning.
+    llvm::once_flag m_checksum_warning_once_flag;
+
     // Keep the modification time that this file data is valid for
     llvm::sys::TimePoint<> m_mod_time;
 

lldb/source/Core/SourceManager.cpp

@@ -61,6 +61,12 @@ static void resolve_tilde(FileSpec &file_spec) {
   }
 }
 
+static std::string toString(const Checksum &checksum) {
+  if (!checksum)
+    return "";
+  return std::string(llvm::formatv("{0}", checksum.digest()));
+}
+
 // SourceManager constructor
 SourceManager::SourceManager(const TargetSP &target_sp)
     : m_last_support_file_sp(std::make_shared<SupportFile>()), m_last_line(0),
@@ -302,6 +308,18 @@ size_t SourceManager::DisplaySourceLinesWithLineNumbersUsingLastFile(
         break;
       }
     }
+
+    Checksum line_table_checksum =
+        last_file_sp->GetSupportFile()->GetChecksum();
+    Checksum on_disk_checksum = last_file_sp->GetChecksum();
+    if (line_table_checksum && line_table_checksum != on_disk_checksum)
+      Debugger::ReportWarning(
+          llvm::formatv(
+              "{0}: source file checksum mismatch between line table "
+              "({1}) and file on disk ({2})",
+              last_file_sp->GetSupportFile()->GetSpecOnly().GetFilename(),
+              toString(line_table_checksum), toString(on_disk_checksum)),
+          std::nullopt, &last_file_sp->GetChecksumWarningOnceFlag());
   }
   return *delta;
 }
@@ -837,12 +855,6 @@ SourceManager::FileSP SourceManager::SourceFileCache::FindSourceFile(
   return {};
 }
 
-static std::string toString(const Checksum &checksum) {
-  if (!checksum)
-    return "";
-  return std::string(llvm::formatv("{0}", checksum.digest()));
-}
-
 void SourceManager::SourceFileCache::Dump(Stream &stream) const {
   // clang-format off
   stream << "Modification time   MD5 Checksum (on-disk)           MD5 Checksum (line table)        Lines    Path\n";

lldb/test/Shell/SymbolFile/Inputs/main.c

@@ -0,0 +1,4 @@
+int main(int argc, char **argv) {
+  // Break on main.
+  return 1;
+}

lldb/test/Shell/SymbolFile/checksum-mismatch.test

@@ -0,0 +1,7 @@
+RUN: mkdir -p %t
+RUN: cp %S/Inputs/main.c %t/main.c
+RUN: %clang_host %t/main.c -std=c99 -gdwarf-5 -o %t/main.out
+RUN: echo "// Modify source file hash" >> %t/main.c
+RUN: %lldb -b %t/main.out -o 'b main' -o 'r' 2>&1 | FileCheck %s
+
+CHECK: warning: main.c: source file checksum mismatch between line table ({{.*}}) and file on disk ({{.*}})