Improve FreeBSD kernel debugging

FreeBSD kernel modules are actually relocatable (.o) ELF files and this
previously caused some issues for LLDB. This change addresses these when
using lldb to symbolicate FreeBSD kernel backtraces. 

The major problems:

- Relocations were not being applied to the DWARF debug info despite
  there being code to do this. Several issues prevented it from working:

  - Relocations are computed at the same time as the symbol table, but
    in the case of split debug files, symbol table parsing always
    redirects to the primary object file, meaning that relocations would
    never be applied in the debug file.

  - There's actually no guarantee that the symbol table has been parsed
    yet when trying to parse debug information.

  - When actually applying relocations, it will segfault because the
    object files are not mapped with MAP_PRIVATE and PROT_WRITE.

- LLDB returned invalid results when performing ordinary address-to-
  symbol resolution. It turned out that the addresses specified in the
  section headers were all 0, so LLDB believed all the sections had
  overlapping "file addresses" and would sometimes return a symbol from
  the wrong section.

Patch by Brian Koropoff

Differential Revision:	https://reviews.llvm.org/D38142

llvm-svn: 314672

11 files changed, 126 insertions, 60 deletions

diff --git a/lldb/include/lldb/Core/Section.h b/lldb/include/lldb/Core/Section.h
index 0466693edbc..2d5d6443ba7 100644
--- a/lldb/include/lldb/Core/Section.h
+++ b/lldb/include/lldb/Core/Section.h
@@ -238,7 +238,7 @@ public:
   ///     section has no data or \a offset is not a valid offset
   ///     in this section.
   //------------------------------------------------------------------
-  lldb::offset_t GetSectionData(DataExtractor &data) const;
+  lldb::offset_t GetSectionData(DataExtractor &data);
 
   uint32_t GetLog2Align() { return m_log2align; }
 
@@ -247,6 +247,10 @@ public:
   // Get the number of host bytes required to hold a target byte
   uint32_t GetTargetByteSize() const { return m_target_byte_size; }
 
+  bool IsRelocated() const { return m_relocated; }
+
+  void SetIsRelocated(bool b) { m_relocated = b; }
+
 protected:
   ObjectFile *m_obj_file;   // The object file that data for this section should
                             // be read from
@@ -274,7 +278,8 @@ protected:
       m_thread_specific : 1,   // This section is thread specific
       m_readable : 1,          // If this section has read permissions
       m_writable : 1,          // If this section has write permissions
-      m_executable : 1;        // If this section has executable permissions
+      m_executable : 1,        // If this section has executable permissions
+      m_relocated : 1;         // If this section has had relocations applied
   uint32_t m_target_byte_size; // Some architectures have non-8-bit byte size.
                                // This is specified as
                                // as a multiple number of a host bytes
diff --git a/lldb/include/lldb/Symbol/ArmUnwindInfo.h b/lldb/include/lldb/Symbol/ArmUnwindInfo.h
index ef67a31e7d0..422408b034c 100644
--- a/lldb/include/lldb/Symbol/ArmUnwindInfo.h
+++ b/lldb/include/lldb/Symbol/ArmUnwindInfo.h
@@ -31,7 +31,7 @@ namespace lldb_private {
 
 class ArmUnwindInfo {
 public:
-  ArmUnwindInfo(const ObjectFile &objfile, lldb::SectionSP &arm_exidx,
+  ArmUnwindInfo(ObjectFile &objfile, lldb::SectionSP &arm_exidx,
                 lldb::SectionSP &arm_extab);
 
   ~ArmUnwindInfo();
diff --git a/lldb/include/lldb/Symbol/ObjectFile.h b/lldb/include/lldb/Symbol/ObjectFile.h
index a4c7b01ece1..60a748bb39d 100644
--- a/lldb/include/lldb/Symbol/ObjectFile.h
+++ b/lldb/include/lldb/Symbol/ObjectFile.h
@@ -352,6 +352,12 @@ public:
   virtual Symtab *GetSymtab() = 0;
 
   //------------------------------------------------------------------
+  /// Perform relocations on the section if necessary.
+  ///
+  //------------------------------------------------------------------
+  virtual void RelocateSection(lldb_private::Section *section);
+
+  //------------------------------------------------------------------
   /// Appends a Symbol for the specified so_addr to the symbol table.
   ///
   /// If verify_unique is false, the symbol table is not searched
@@ -792,15 +798,15 @@ public:
 
   size_t CopyData(lldb::offset_t offset, size_t length, void *dst) const;
 
-  virtual size_t ReadSectionData(const Section *section,
+  virtual size_t ReadSectionData(Section *section,
                                  lldb::offset_t section_offset, void *dst,
-                                 size_t dst_len) const;
+                                 size_t dst_len);
 
-  virtual size_t ReadSectionData(const Section *section,
-                                 DataExtractor &section_data) const;
+  virtual size_t ReadSectionData(Section *section,
+                                 DataExtractor &section_data);
 
-  size_t MemoryMapSectionData(const Section *section,
-                              DataExtractor &section_data) const;
+  size_t MemoryMapSectionData(Section *section,
+                              DataExtractor &section_data);
 
   bool IsInMemory() const { return m_memory_addr != LLDB_INVALID_ADDRESS; }
 
diff --git a/lldb/source/Core/Section.cpp b/lldb/source/Core/Section.cpp
index 2ea497eba56..c9faf9f8915 100644
--- a/lldb/source/Core/Section.cpp
+++ b/lldb/source/Core/Section.cpp
@@ -135,7 +135,7 @@ Section::Section(const ModuleSP &module_sp, ObjectFile *obj_file,
       m_file_offset(file_offset), m_file_size(file_size),
       m_log2align(log2align), m_children(), m_fake(false), m_encrypted(false),
       m_thread_specific(false), m_readable(false), m_writable(false),
-      m_executable(false), m_target_byte_size(target_byte_size) {
+      m_executable(false), m_relocated(false), m_target_byte_size(target_byte_size) {
   //    printf ("Section::Section(%p): module=%p, sect_id = 0x%16.16" PRIx64 ",
   //    addr=[0x%16.16" PRIx64 " - 0x%16.16" PRIx64 "), file [0x%16.16" PRIx64 "
   //    - 0x%16.16" PRIx64 "), flags = 0x%8.8x, name = %s\n",
@@ -157,7 +157,7 @@ Section::Section(const lldb::SectionSP &parent_section_sp,
       m_file_offset(file_offset), m_file_size(file_size),
       m_log2align(log2align), m_children(), m_fake(false), m_encrypted(false),
       m_thread_specific(false), m_readable(false), m_writable(false),
-      m_executable(false), m_target_byte_size(target_byte_size) {
+      m_executable(false), m_relocated(false), m_target_byte_size(target_byte_size) {
   //    printf ("Section::Section(%p): module=%p, sect_id = 0x%16.16" PRIx64 ",
   //    addr=[0x%16.16" PRIx64 " - 0x%16.16" PRIx64 "), file [0x%16.16" PRIx64 "
   //    - 0x%16.16" PRIx64 "), flags = 0x%8.8x, name = %s.%s\n",
@@ -392,7 +392,7 @@ lldb::offset_t Section::GetSectionData(void *dst, lldb::offset_t dst_len,
   return 0;
 }
 
-lldb::offset_t Section::GetSectionData(DataExtractor &section_data) const {
+lldb::offset_t Section::GetSectionData(DataExtractor &section_data) {
   if (m_obj_file)
     return m_obj_file->ReadSectionData(this, section_data);
   return 0;
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
index 0f67ab5f33c..e431d4a08f9 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.cpp
@@ -405,7 +405,7 @@ ObjectFile *ObjectFileELF::CreateInstance(const lldb::ModuleSP &module_sp,
                                           lldb::offset_t length) {
   if (!data_sp) {
     data_sp =
-        DataBufferLLVM::CreateSliceFromPath(file->GetPath(), length, file_offset);
+        DataBufferLLVM::CreateSliceFromPath(file->GetPath(), length, file_offset, true);
     if (!data_sp)
       return nullptr;
     data_offset = 0;
@@ -423,7 +423,7 @@ ObjectFile *ObjectFileELF::CreateInstance(const lldb::ModuleSP &module_sp,
   // Update the data to contain the entire file if it doesn't already
   if (data_sp->GetByteSize() < length) {
     data_sp =
-        DataBufferLLVM::CreateSliceFromPath(file->GetPath(), length, file_offset);
+        DataBufferLLVM::CreateSliceFromPath(file->GetPath(), length, file_offset, true);
     if (!data_sp)
       return nullptr;
     data_offset = 0;
@@ -1818,6 +1818,12 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
   if (!m_sections_ap.get() && ParseSectionHeaders()) {
     m_sections_ap.reset(new SectionList());
 
+    // Object files frequently have 0 for every section address, meaning we
+    // need to compute synthetic addresses in order for "file addresses" from
+    // different sections to not overlap
+    bool synthaddrs = (CalculateType() == ObjectFile::Type::eTypeObjectFile);
+    uint64_t nextaddr = 0;
+
     for (SectionHeaderCollIter I = m_section_headers.begin();
          I != m_section_headers.end(); ++I) {
       const ELFSectionHeaderInfo &header = *I;
@@ -1990,11 +1996,18 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
               ? m_arch_spec.GetDataByteSize()
               : eSectionTypeCode == sect_type ? m_arch_spec.GetCodeByteSize()
                                               : 1;
-      const addr_t sect_file_addr = header.sh_flags & SHF_ALLOC
-                                                    ? header.sh_addr
-                                                    : LLDB_INVALID_ADDRESS;
       elf::elf_xword log2align =
           (header.sh_addralign == 0) ? 0 : llvm::Log2_64(header.sh_addralign);
+
+      uint64_t addr = header.sh_addr;
+
+      if ((header.sh_flags & SHF_ALLOC) && synthaddrs) {
+          nextaddr =
+              (nextaddr + header.sh_addralign - 1) & ~(header.sh_addralign - 1);
+          addr = nextaddr;
+          nextaddr += vm_size;
+      }
+
       SectionSP section_sp(new Section(
           GetModule(), // Module to which this section belongs.
           this, // ObjectFile to which this section belongs and should read
@@ -2002,7 +2015,7 @@ void ObjectFileELF::CreateSections(SectionList &unified_section_list) {
           SectionIndex(I),     // Section ID.
           name,                // Section name.
           sect_type,           // Section type.
-          sect_file_addr,      // VM address.
+          addr,                // VM address.
           vm_size,             // VM size in bytes of this section.
           header.sh_offset,    // Offset of this section in the file.
           file_size,           // Size of the section as found in the file.
@@ -2720,7 +2733,7 @@ ObjectFileELF::ParseTrampolineSymbols(Symtab *symbol_table, user_id_t start_id,
                              rel_data, symtab_data, strtab_data);
 }
 
-unsigned ObjectFileELF::RelocateSection(
+unsigned ObjectFileELF::ApplyRelocations(
     Symtab *symtab, const ELFHeader *hdr, const ELFSectionHeader *rel_hdr,
     const ELFSectionHeader *symtab_hdr, const ELFSectionHeader *debug_hdr,
     DataExtractor &rel_data, DataExtractor &symtab_data,
@@ -2797,7 +2810,8 @@ unsigned ObjectFileELF::RelocateSection(
 }
 
 unsigned ObjectFileELF::RelocateDebugSections(const ELFSectionHeader *rel_hdr,
-                                              user_id_t rel_id) {
+                                              user_id_t rel_id,
+                                              lldb_private::Symtab *thetab) {
   assert(rel_hdr->sh_type == SHT_RELA || rel_hdr->sh_type == SHT_REL);
 
   // Parse in the section list if needed.
@@ -2833,10 +2847,11 @@ unsigned ObjectFileELF::RelocateDebugSections(const ELFSectionHeader *rel_hdr,
   DataExtractor symtab_data;
   DataExtractor debug_data;
 
-  if (ReadSectionData(rel, rel_data) && ReadSectionData(symtab, symtab_data) &&
-      ReadSectionData(debug, debug_data)) {
-    RelocateSection(m_symtab_ap.get(), &m_header, rel_hdr, symtab_hdr,
-                    debug_hdr, rel_data, symtab_data, debug_data, debug);
+  if (GetData(rel->GetFileOffset(), rel->GetFileSize(), rel_data) &&
+      GetData(symtab->GetFileOffset(), symtab->GetFileSize(), symtab_data) &&
+      GetData(debug->GetFileOffset(), debug->GetFileSize(), debug_data)) {
+    ApplyRelocations(thetab, &m_header, rel_hdr, symtab_hdr, debug_hdr,
+                     rel_data, symtab_data, debug_data, debug);
   }
 
   return 0;
@@ -2930,21 +2945,48 @@ Symtab *ObjectFileELF::GetSymtab() {
     m_symtab_ap->CalculateSymbolSizes();
   }
 
+  return m_symtab_ap.get();
+}
+
+void ObjectFileELF::RelocateSection(lldb_private::Section *section)
+{
+  static const char *debug_prefix = ".debug";
+
+  // Set relocated bit so we stop getting called, regardless of
+  // whether we actually relocate.
+  section->SetIsRelocated(true);
+
+  // We only relocate in ELF relocatable files
+  if (CalculateType() != eTypeObjectFile)
+    return;
+
+  const char *section_name = section->GetName().GetCString();
+  // Can't relocate that which can't be named
+  if (section_name == nullptr)
+    return;
+
+  // We don't relocate non-debug sections at the moment
+  if (strncmp(section_name, debug_prefix, strlen(debug_prefix)))
+    return;
+
+  // Relocation section names to look for
+  std::string needle = std::string(".rel") + section_name;
+  std::string needlea = std::string(".rela") + section_name;
+
   for (SectionHeaderCollIter I = m_section_headers.begin();
        I != m_section_headers.end(); ++I) {
     if (I->sh_type == SHT_RELA || I->sh_type == SHT_REL) {
-      if (CalculateType() == eTypeObjectFile) {
-        const char *section_name = I->section_name.AsCString("");
-        if (strstr(section_name, ".rela.debug") ||
-            strstr(section_name, ".rel.debug")) {
-          const ELFSectionHeader &reloc_header = *I;
-          user_id_t reloc_id = SectionIndex(I);
-          RelocateDebugSections(&reloc_header, reloc_id);
-        }
+      const char *hay_name = I->section_name.GetCString();
+      if (hay_name == nullptr)
+        continue;
+      if (needle == hay_name || needlea == hay_name) {
+        const ELFSectionHeader &reloc_header = *I;
+        user_id_t reloc_id = SectionIndex(I);
+        RelocateDebugSections(&reloc_header, reloc_id, GetSymtab());
+        break;
       }
     }
   }
-  return m_symtab_ap.get();
 }
 
 void ObjectFileELF::ParseUnwindSymbols(Symtab *symbol_table,
diff --git a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.h b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.h
index 6d8717b0ef2..e0478cc0697 100644
--- a/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.h
+++ b/lldb/source/Plugins/ObjectFile/ELF/ObjectFileELF.h
@@ -154,6 +154,8 @@ public:
   llvm::StringRef
   StripLinkerSymbolAnnotations(llvm::StringRef symbol_name) const override;
 
+  void RelocateSection(lldb_private::Section *section) override;
+
 private:
   ObjectFileELF(const lldb::ModuleSP &module_sp, lldb::DataBufferSP &data_sp,
                 lldb::offset_t data_offset, const lldb_private::FileSpec *file,
@@ -296,17 +298,18 @@ private:
 
   /// Relocates debug sections
   unsigned RelocateDebugSections(const elf::ELFSectionHeader *rel_hdr,
-                                 lldb::user_id_t rel_id);
-
-  unsigned RelocateSection(lldb_private::Symtab *symtab,
-                           const elf::ELFHeader *hdr,
-                           const elf::ELFSectionHeader *rel_hdr,
-                           const elf::ELFSectionHeader *symtab_hdr,
-                           const elf::ELFSectionHeader *debug_hdr,
-                           lldb_private::DataExtractor &rel_data,
-                           lldb_private::DataExtractor &symtab_data,
-                           lldb_private::DataExtractor &debug_data,
-                           lldb_private::Section *rel_section);
+                                 lldb::user_id_t rel_id,
+                                 lldb_private::Symtab *thetab);
+
+  unsigned ApplyRelocations(lldb_private::Symtab *symtab,
+                            const elf::ELFHeader *hdr,
+                            const elf::ELFSectionHeader *rel_hdr,
+                            const elf::ELFSectionHeader *symtab_hdr,
+                            const elf::ELFSectionHeader *debug_hdr,
+                            lldb_private::DataExtractor &rel_data,
+                            lldb_private::DataExtractor &symtab_data,
+                            lldb_private::DataExtractor &debug_data,
+                            lldb_private::Section *rel_section);
 
   /// Loads the section name string table into m_shstr_data.  Returns the
   /// number of bytes constituting the table.
diff --git a/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.cpp b/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.cpp
index 06406c6f165..90982e8db9e 100644
--- a/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.cpp
+++ b/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.cpp
@@ -230,9 +230,9 @@ bool ObjectFileJIT::SetLoadAddress(Target &target, lldb::addr_t value,
   return num_loaded_sections > 0;
 }
 
-size_t ObjectFileJIT::ReadSectionData(const lldb_private::Section *section,
+size_t ObjectFileJIT::ReadSectionData(lldb_private::Section *section,
                                       lldb::offset_t section_offset, void *dst,
-                                      size_t dst_len) const {
+                                      size_t dst_len) {
   lldb::offset_t file_size = section->GetFileSize();
   if (section_offset < file_size) {
     size_t src_len = file_size - section_offset;
@@ -248,8 +248,8 @@ size_t ObjectFileJIT::ReadSectionData(const lldb_private::Section *section,
 }
 
 size_t ObjectFileJIT::ReadSectionData(
-    const lldb_private::Section *section,
-    lldb_private::DataExtractor &section_data) const {
+    lldb_private::Section *section,
+    lldb_private::DataExtractor &section_data) {
   if (section->GetFileSize()) {
     const void *src = (void *)(uintptr_t)section->GetFileOffset();
 
diff --git a/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.h b/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.h
index a211645d5d8..c964906a5e8 100644
--- a/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.h
+++ b/lldb/source/Plugins/ObjectFile/JIT/ObjectFileJIT.h
@@ -83,13 +83,13 @@ public:
 
   uint32_t GetDependentModules(lldb_private::FileSpecList &files) override;
 
-  size_t ReadSectionData(const lldb_private::Section *section,
+  size_t ReadSectionData(lldb_private::Section *section,
                          lldb::offset_t section_offset, void *dst,
-                         size_t dst_len) const override;
+                         size_t dst_len) override;
 
   size_t
-  ReadSectionData(const lldb_private::Section *section,
-                  lldb_private::DataExtractor &section_data) const override;
+  ReadSectionData(lldb_private::Section *section,
+                  lldb_private::DataExtractor &section_data) override;
 
   lldb_private::Address GetEntryPointAddress() override;
 
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index 4642c2e14dd..27752da86eb 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -436,7 +436,7 @@ void SymbolFileDWARF::InitializeObject() {
   ModuleSP module_sp(m_obj_file->GetModule());
   if (module_sp) {
     const SectionList *section_list = module_sp->GetSectionList();
-    const Section *section =
+    Section *section =
         section_list->FindSectionByName(GetDWARFMachOSegmentName()).get();
 
     // Memory map the DWARF mach-o segment so we have everything mmap'ed
diff --git a/lldb/source/Symbol/ArmUnwindInfo.cpp b/lldb/source/Symbol/ArmUnwindInfo.cpp
index 742c057e10e..4da307bf0c3 100644
--- a/lldb/source/Symbol/ArmUnwindInfo.cpp
+++ b/lldb/source/Symbol/ArmUnwindInfo.cpp
@@ -46,7 +46,7 @@ bool ArmUnwindInfo::ArmExidxEntry::operator<(const ArmExidxEntry &other) const {
   return address < other.address;
 }
 
-ArmUnwindInfo::ArmUnwindInfo(const ObjectFile &objfile, SectionSP &arm_exidx,
+ArmUnwindInfo::ArmUnwindInfo(ObjectFile &objfile, SectionSP &arm_exidx,
                              SectionSP &arm_extab)
     : m_byte_order(objfile.GetByteOrder()), m_arm_exidx_sp(arm_exidx),
       m_arm_extab_sp(arm_extab) {
diff --git a/lldb/source/Symbol/ObjectFile.cpp b/lldb/source/Symbol/ObjectFile.cpp
index c2e2be9cfb7..39593bc6e2b 100644
--- a/lldb/source/Symbol/ObjectFile.cpp
+++ b/lldb/source/Symbol/ObjectFile.cpp
@@ -483,9 +483,9 @@ size_t ObjectFile::CopyData(lldb::offset_t offset, size_t length,
   return m_data.CopyData(offset, length, dst);
 }
 
-size_t ObjectFile::ReadSectionData(const Section *section,
+size_t ObjectFile::ReadSectionData(Section *section,
                                    lldb::offset_t section_offset, void *dst,
-                                   size_t dst_len) const {
+                                   size_t dst_len) {
   assert(section);
   section_offset *= section->GetTargetByteSize();
 
@@ -505,6 +505,9 @@ size_t ObjectFile::ReadSectionData(const Section *section,
                                       dst_len, error);
     }
   } else {
+    if (!section->IsRelocated())
+      RelocateSection(section);
+
     const lldb::offset_t section_file_size = section->GetFileSize();
     if (section_offset < section_file_size) {
       const size_t section_bytes_left = section_file_size - section_offset;
@@ -531,8 +534,8 @@ size_t ObjectFile::ReadSectionData(const Section *section,
 //----------------------------------------------------------------------
 // Get the section data the file on disk
 //----------------------------------------------------------------------
-size_t ObjectFile::ReadSectionData(const Section *section,
-                                   DataExtractor &section_data) const {
+size_t ObjectFile::ReadSectionData(Section *section,
+                                   DataExtractor &section_data) {
   // If some other objectfile owns this data, pass this to them.
   if (section->GetObjectFile() != this)
     return section->GetObjectFile()->ReadSectionData(section, section_data);
@@ -562,8 +565,8 @@ size_t ObjectFile::ReadSectionData(const Section *section,
   }
 }
 
-size_t ObjectFile::MemoryMapSectionData(const Section *section,
-                                        DataExtractor &section_data) const {
+size_t ObjectFile::MemoryMapSectionData(Section *section,
+                                        DataExtractor &section_data) {
   // If some other objectfile owns this data, pass this to them.
   if (section->GetObjectFile() != this)
     return section->GetObjectFile()->MemoryMapSectionData(section,
@@ -572,6 +575,9 @@ size_t ObjectFile::MemoryMapSectionData(const Section *section,
   if (IsInMemory()) {
     return ReadSectionData(section, section_data);
   } else {
+    if (!section->IsRelocated())
+      RelocateSection(section);
+
     // The object file now contains a full mmap'ed copy of the object file data,
     // so just use this
     return GetData(section->GetFileOffset(), section->GetFileSize(),
@@ -694,3 +700,7 @@ Status ObjectFile::LoadInMemory(Target &target, bool set_pc) {
   }
   return error;
 }
+
+void ObjectFile::RelocateSection(lldb_private::Section *section)
+{
+}