commit d13f691f41c94b8681829c85ecb7a23fcbb9caf1
author Ed Maste <emaste@freebsd.org> Mon Oct 02 14:35:07 2017 +0000
committer Ed Maste <emaste@freebsd.org> Mon Oct 02 14:35:07 2017 +0000
tree 42395ba6f8765094749b3337d444e2fbc1aa11d9
parent e2aa5b2ace432d24be067044a333128514b46faf

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

lldb/source/Symbol/ObjectFile.cpp

diff --git a/lldb/source/Symbol/ObjectFile.cpp b/lldb/source/Symbol/ObjectFile.cpp
index c2e2be9..39593bc 100644
--- a/lldb/source/Symbol/ObjectFile.cpp
+++ b/lldb/source/Symbol/ObjectFile.cpp
@@ -483,9 +483,9 @@
   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 @@
                                       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 @@
 //----------------------------------------------------------------------
 // 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::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 @@
   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 @@
   }
   return error;
 }
+
+void ObjectFile::RelocateSection(lldb_private::Section *section)
+{
+}