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

1 files changed, 16 insertions, 6 deletions

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)
+{
+}