[LLDB] Fix debuginfo ELF files overwriting Unified Section List

lldb/include/lldb/Core/Section.h

@@ -96,6 +96,17 @@ class SectionList {
   /// information.
   uint64_t GetDebugInfoSize() const;
 
+  // Callback to decide which of two matching sections should be used in the
+  // merged output.
+  using MergeCallback =
+      std::function<lldb::SectionSP(lldb::SectionSP, lldb::SectionSP)>;
+
+  // Function that merges two different sections into a new output list. All
+  // unique sections will be checked for conflict and resolved using the
+  // supplied merging callback.
+  static std::shared_ptr<SectionList> Merge(SectionList &lhs, SectionList &rhs,
+                                            MergeCallback filter);
+
 protected:
   collection m_sections;
 };

lldb/source/Core/Section.cpp

@@ -683,6 +683,34 @@ uint64_t SectionList::GetDebugInfoSize() const {
   return debug_info_size;
 }
 
+std::shared_ptr<SectionList>
+SectionList::Merge(SectionList &lhs, SectionList &rhs, MergeCallback filter) {
+  std::shared_ptr<SectionList> output_sp = std::make_shared<SectionList>();
+
+  // Iterate through all the sections in lhs and see if we have matches in
+  // the rhs list.
+  for (const auto &lhs_section : lhs) {
+    auto rhs_section = rhs.FindSectionByName(lhs_section->GetName());
+    if (rhs_section) {
+      assert(lhs_section->GetName() == rhs_section->GetName());
+      output_sp->AddSection(filter(lhs_section, rhs_section));
+    } else
+      output_sp->AddSection(lhs_section);
+  }
+
+  // Now that we've visited all possible duplicates, we can iterate over
+  // the rhs and take any values not in lhs.
+  for (const auto &rhs_section : rhs) {
+    auto lhs_section = lhs.FindSectionByName(rhs_section->GetName());
+    // Because we already visited everything overlapping between rhs
+    // and lhs, any section not in lhs is unique and can be output.
+    if (!lhs_section)
+      output_sp->AddSection(rhs_section);
+  }
+
+  return output_sp;
+}
+
 namespace llvm {
 namespace json {
 

lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp

@@ -130,6 +130,42 @@ class ELFRelocation {
 
   RelocUnion reloc;
 };
+
+lldb::SectionSP MergeSections(lldb::SectionSP lhs, lldb::SectionSP rhs) {
+  assert(lhs && rhs);
+
+  // We only take the RHS is the LHS is SHT_NOBITS, which would be
+  // represented as a size of 0. Where we can take the rhs.
+  if (lhs->GetByteSize() == 0)
+    return rhs;
+
+  lldb::ModuleSP lhs_module_parent = lhs->GetModule();
+  lldb::ModuleSP rhs_module_parent = rhs->GetModule();
+  assert(lhs_module_parent && rhs_module_parent);
+
+  // Now that we're taking the lhs, we should do some sanity checks to warn the
+  // user if this debuginfo/dwp looks invalid. However if RHS is SHT_NO_BITS
+  // we want to ignore the size comparison.
+  if (rhs->GetByteSize() > 0 && lhs->GetByteSize() != rhs->GetByteSize())
+    lhs_module_parent->ReportWarning(
+        "Mismatched size for section {0} when merging with {1}, expected: "
+        "{2:x}, "
+        "actual: {3:x}",
+        lhs->GetTypeAsCString(),
+        rhs_module_parent->GetFileSpec().GetPathAsConstString().GetCString(),
+        lhs->GetByteSize(), rhs->GetByteSize());
+
+  if (lhs->GetFileAddress() != rhs->GetFileAddress())
+    lhs_module_parent->ReportWarning(
+        "Mismatch addresses for section {0} when "
+        "merging with {1}, expected: {2:x}, "
+        "actual: {3:x}",
+        lhs->GetTypeAsCString(),
+        rhs_module_parent->GetFileSpec().GetPathAsConstString().GetCString(),
+        lhs->GetByteSize(), rhs->GetByteSize());
+
+  return lhs;
+}
 } // end anonymous namespace
 
 ELFRelocation::ELFRelocation(unsigned type) {
@@ -1967,10 +2003,11 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
     provider.AddSection(std::move(*InfoOr), std::move(section_sp));
   }
 
-  // For eTypeDebugInfo files, the Symbol Vendor will take care of updating the
-  // unified section list.
-  if (GetType() != eTypeDebugInfo)
-    unified_section_list = *m_sections_up;
+  // Merge the two adding any new sections, and overwriting any existing
+  // sections that are SHT_NOBITS
+  std::shared_ptr<SectionList> merged_section_list =
+      SectionList::Merge(unified_section_list, *m_sections_up, MergeSections);
+  unified_section_list = *merged_section_list;
 
   // If there's a .gnu_debugdata section, we'll try to read the .symtab that's
   // embedded in there and replace the one in the original object file (if any).

lldb/test/API/python_api/unified_section_list/Makefile

@@ -0,0 +1,5 @@
+CXX_SOURCES := main.cpp
+
+SPLIT_DEBUG_SYMBOLS := YES
+
+include Makefile.rules

lldb/test/API/python_api/unified_section_list/TestModuleUnifiedSectionList.py

@@ -0,0 +1,51 @@
+"""
+Test Unified Section List merging.
+"""
+
+import os
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+from lldbsuite.test.lldbutil import symbol_type_to_str
+
+
+class ModuleUnifiedSectionList(TestBase):
+    @skipUnlessPlatform(["linux", "freebsd", "netbsd"])
+    def test_unified_section_list(self):
+        self.build()
+        exe = self.getBuildArtifact("a.out")
+        debug_info = self.getBuildArtifact("a.out.debug")
+        new_dir = os.path.join(os.path.dirname(debug_info), "new_dir")
+        os.mkdir(new_dir)
+        renamed_debug_info = os.path.join(new_dir, "renamed.debug")
+        os.rename(debug_info, renamed_debug_info)
+        target = self.dbg.CreateTarget(exe)
+        self.assertTrue(target, VALID_TARGET)
+        self.assertGreater(target.GetNumModules(), 0)
+
+        main_exe_module = target.GetModuleAtIndex(0)
+        eh_frame = main_exe_module.FindSection(".eh_frame")
+        self.assertTrue(eh_frame.IsValid())
+        self.assertGreater(eh_frame.size, 0)
+
+        # Should be stripped in main executable.
+        debug_info_section = main_exe_module.FindSection(".debug_info")
+        self.assertFalse(debug_info_section.IsValid())
+
+        ci = self.dbg.GetCommandInterpreter()
+        res = lldb.SBCommandReturnObject()
+        ci.HandleCommand(f"target symbols add {renamed_debug_info}", res)
+        self.assertTrue(res.Succeeded())
+
+        # Should be stripped in .debuginfo but be present in main executable.
+        main_exe_module = target.GetModuleAtIndex(0)
+        eh_frame = main_exe_module.FindSection(".eh_frame")
+        self.assertTrue(eh_frame.IsValid())
+        self.assertGreater(eh_frame.size, 0)
+
+        # Should be unified and both sections should have contents.
+        debug_info_section = main_exe_module.FindSection(".debug_info")
+        self.assertTrue(debug_info_section.IsValid())
+        self.assertGreater(debug_info_section.file_size, 0)

lldb/test/API/python_api/unified_section_list/main.cpp

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+int main() { printf("Hello World\n"); }