ObjectFileELF: permit thread-local sections with overlapping file addresses

Summary:
In an attempt to make file-address-based lookups more predictable, in D55998
we started ignoring sections which would result in file address
overlaps. It turns out this was too aggressive because thread-local
sections typically will have file addresses which apear to overlap
regular data/code. This does not cause a problem at runtime because
thread-local sections are loaded into memory using special logic, but it
can cause problems for lldb when trying to lookup objects by their file
address.

This patch changes ObjectFileELF to permit thread-local sections to
overlap regular ones by essentially giving them a separate address
space. It also makes them more symmetrical to regular sections by
creating container sections from PT_TLS segments.

Simultaneously, the patch changes the regular file address lookup logic
to ignore sections with the thread-specific bit set. I believe this is
what the users looking up file addresses would typically expect, as
looking up thread-local data generally requires more complex logic (e.g.
DWARF has a special opcode for that).

Reviewers: clayborg, jingham, MaskRay

Subscribers: emaste, aprantl, arichardson, lldb-commits

Differential Revision: https://reviews.llvm.org/D65282

llvm-svn: 368010

1 files changed, 29 insertions, 16 deletions

diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index 50d6b8f864c..9f8ab3761c8 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -1712,6 +1712,8 @@ class VMAddressProvider {
   VMMap Segments = VMMap(Alloc);
   VMMap Sections = VMMap(Alloc);
   lldb_private::Log *Log = GetLogIfAllCategoriesSet(LIBLLDB_LOG_MODULES);
+  size_t SegmentCount = 0;
+  std::string SegmentName;
 
   VMRange GetVMRange(const ELFSectionHeader &H) {
     addr_t Address = H.sh_addr;
@@ -1726,18 +1728,23 @@ class VMAddressProvider {
   }
 
 public:
-  VMAddressProvider(ObjectFile::Type Type) : ObjectType(Type) {}
+  VMAddressProvider(ObjectFile::Type Type, llvm::StringRef SegmentName)
+      : ObjectType(Type), SegmentName(SegmentName) {}
+
+  std::string GetNextSegmentName() const {
+    return llvm::formatv("{0}[{1}]", SegmentName, SegmentCount).str();
+  }
 
   llvm::Optional<VMRange> GetAddressInfo(const ELFProgramHeader &H) {
     if (H.p_memsz == 0) {
-      LLDB_LOG(Log,
-               "Ignoring zero-sized PT_LOAD segment. Corrupt object file?");
+      LLDB_LOG(Log, "Ignoring zero-sized {0} segment. Corrupt object file?",
+               SegmentName);
       return llvm::None;
     }
 
     if (Segments.overlaps(H.p_vaddr, H.p_vaddr + H.p_memsz)) {
-      LLDB_LOG(Log,
-               "Ignoring overlapping PT_LOAD segment. Corrupt object file?");
+      LLDB_LOG(Log, "Ignoring overlapping {0} segment. Corrupt object file?",
+               SegmentName);
       return llvm::None;
     }
     return VMRange(H.p_vaddr, H.p_memsz);
@@ -1772,6 +1779,7 @@ public:
 
   void AddSegment(const VMRange &Range, SectionSP Seg) {
     Segments.insert(Range.GetRangeBase(), Range.GetRangeEnd(), std::move(Seg));
+    ++SegmentCount;
   }
 
   void AddSection(SectionAddressInfo Info, SectionSP Sect) {
@@ -1790,28 +1798,31 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
     return;
 
   m_sections_up = llvm::make_unique<SectionList>();
-  VMAddressProvider address_provider(GetType());
+  VMAddressProvider regular_provider(GetType(), "PT_LOAD");
+  VMAddressProvider tls_provider(GetType(), "PT_TLS");
 
-  size_t LoadID = 0;
   for (const auto &EnumPHdr : llvm::enumerate(ProgramHeaders())) {
     const ELFProgramHeader &PHdr = EnumPHdr.value();
-    if (PHdr.p_type != PT_LOAD)
+    if (PHdr.p_type != PT_LOAD && PHdr.p_type != PT_TLS)
       continue;
 
-    auto InfoOr = address_provider.GetAddressInfo(PHdr);
+    VMAddressProvider &provider =
+        PHdr.p_type == PT_TLS ? tls_provider : regular_provider;
+    auto InfoOr = provider.GetAddressInfo(PHdr);
     if (!InfoOr)
       continue;
 
-    ConstString Name(("PT_LOAD[" + llvm::Twine(LoadID++) + "]").str());
     uint32_t Log2Align = llvm::Log2_64(std::max<elf_xword>(PHdr.p_align, 1));
     SectionSP Segment = std::make_shared<Section>(
-        GetModule(), this, SegmentID(EnumPHdr.index()), Name,
-        eSectionTypeContainer, InfoOr->GetRangeBase(), InfoOr->GetByteSize(),
-        PHdr.p_offset, PHdr.p_filesz, Log2Align, /*flags*/ 0);
+        GetModule(), this, SegmentID(EnumPHdr.index()),
+        ConstString(provider.GetNextSegmentName()), eSectionTypeContainer,
+        InfoOr->GetRangeBase(), InfoOr->GetByteSize(), PHdr.p_offset,
+        PHdr.p_filesz, Log2Align, /*flags*/ 0);
     Segment->SetPermissions(GetPermissions(PHdr));
+    Segment->SetIsThreadSpecific(PHdr.p_type == PT_TLS);
     m_sections_up->AddSection(Segment);
 
-    address_provider.AddSegment(*InfoOr, std::move(Segment));
+    provider.AddSegment(*InfoOr, std::move(Segment));
   }
 
   ParseSectionHeaders();
@@ -1826,7 +1837,9 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
     const uint64_t file_size =
         header.sh_type == SHT_NOBITS ? 0 : header.sh_size;
 
-    auto InfoOr = address_provider.GetAddressInfo(header);
+    VMAddressProvider &provider =
+        header.sh_flags & SHF_TLS ? tls_provider : regular_provider;
+    auto InfoOr = provider.GetAddressInfo(header);
     if (!InfoOr)
       continue;
 
@@ -1857,7 +1870,7 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
     section_sp->SetIsThreadSpecific(header.sh_flags & SHF_TLS);
     (InfoOr->Segment ? InfoOr->Segment->GetChildren() : *m_sections_up)
         .AddSection(section_sp);
-    address_provider.AddSection(std::move(*InfoOr), std::move(section_sp));
+    provider.AddSection(std::move(*InfoOr), std::move(section_sp));
   }
 
   // For eTypeDebugInfo files, the Symbol Vendor will take care of updating the