Add debug fission support.

src/common/dwarf/dwarf2reader.h

Index: src/common/dwarf/dwarf2reader.h
diff --git a/src/common/dwarf/dwarf2reader.h b/src/common/dwarf/dwarf2reader.h
index 1f5b37a04d9d34c120bb8b70c3aaf7c9a814ce18..47daf9d2a07397d616a9cfecc09a282d3e15a8d0 100644
--- a/src/common/dwarf/dwarf2reader.h
+++ b/src/common/dwarf/dwarf2reader.h
@@ -47,16 +47,19 @@
 #include <string>
 #include <utility>
 #include <vector>
+#include <memory>
 
 #include "common/dwarf/bytereader.h"
 #include "common/dwarf/dwarf2enums.h"
 #include "common/dwarf/types.h"
 #include "common/using_std_string.h"
+#include "common/dwarf/elf_reader.h"
 
 namespace dwarf2reader {
 struct LineStateMachine;
 class Dwarf2Handler;
 class LineInfoHandler;
+class DwpReader;
 
 // This maps from a string naming a section to a pair containing a
 // the data for the section, and the size of the section.
@@ -184,6 +187,107 @@ class LineInfoHandler {
                        uint32 file_num, uint32 line_num, uint32 column_num) { }
 };
 
+// This class is the main interface between the reader and the
+// client.  The virtual functions inside this get called for
+// interesting events that happen during DWARF2 reading.
+// The default implementation skips everything.
+

[ivanpe, 2016/04/27 01:11:44]

No need to leave a blank line.

[yunlian, 2016/04/27 16:35:29]

Done.

+class Dwarf2Handler {
+ public:
+  Dwarf2Handler() { }
+
+  virtual ~Dwarf2Handler() { }
+
+  // Start to process a compilation unit at OFFSET from the beginning of the

[ivanpe, 2016/04/27 01:11:45]

It looks like the code that follows comes from:
https://github.com/google/autofdo/blame/master/symbolize/dwarf2reader.h

Who owns the code?  Has it been reviewed before?

Can you please, include dehao@google.com for review.

+  // .debug_info section. Return false if you would like to skip this
+  // compilation unit.
+  virtual bool StartCompilationUnit(uint64 offset, uint8 address_size,
+                                    uint8 offset_size, uint64 cu_length,
+                                    uint8 dwarf_version) { return false; }
+
+  // When processing a skeleton compilation unit, resulting from a split
+  // DWARF compilation, once the skeleton debug info has been read,
+  // the reader will call this function to ask the client if it needs
+  // the full debug info from the .dwo or .dwp file.  Return true if
+  // you need it, or false to skip processing the split debug info.
+  virtual bool NeedSplitDebugInfo() { return true; }
+
+  // Start to process a split compilation unit at OFFSET from the beginning of
+  // the debug_info section in the .dwp/.dwo file.  Return false if you would
+  // like to skip this compilation unit.
+  virtual bool StartSplitCompilationUnit(uint64 offset,
+                                         uint64 cu_length) { return false; }
+
+  // Start to process a DIE at OFFSET from the beginning of the .debug_info
+  // section. Return false if you would like to skip this DIE.
+  virtual bool StartDIE(uint64 offset, enum DwarfTag tag) { return false; }
+
+  // Called when we have an attribute with unsigned data to give to our
+  // handler. The attribute is for the DIE at OFFSET from the beginning of the
+  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
+  // DATA.
+  virtual void ProcessAttributeUnsigned(uint64 offset,
+                                        enum DwarfAttribute attr,
+                                        enum DwarfForm form,
+                                        uint64 data) { }
+
+  // Called when we have an attribute with signed data to give to our handler.
+  // The attribute is for the DIE at OFFSET from the beginning of the
+  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
+  // DATA.
+  virtual void ProcessAttributeSigned(uint64 offset,
+                                      enum DwarfAttribute attr,
+                                      enum DwarfForm form,
+                                      int64 data) { }
+
+// Called when we have an attribute whose value is a reference to

[ivanpe, 2016/04/27 01:11:44]

indent is off

[yunlian, 2016/04/27 16:35:29]

Done.

+  // another DIE. The attribute belongs to the DIE at OFFSET from the
+  // beginning of the .debug_info section. Its name is ATTR, its form
+  // is FORM, and the offset of the DIE being referred to from the
+  // beginning of the .debug_info section is DATA.
+  virtual void ProcessAttributeReference(uint64 offset,
+                                         enum DwarfAttribute attr,
+                                         enum DwarfForm form,
+                                         uint64 data) { }
+
+  // Called when we have an attribute with a buffer of data to give to our
+  // handler. The attribute is for the DIE at OFFSET from the beginning of the
+  // .debug_info section. Its name is ATTR, its form is FORM, DATA points to
+  // the buffer's contents, and its length in bytes is LENGTH. The buffer is
+  // owned by the caller, not the callee, and may not persist for very long.
+  // If you want the data to be available later, it needs to be copied.
+  virtual void ProcessAttributeBuffer(uint64 offset,
+                                      enum DwarfAttribute attr,
+                                      enum DwarfForm form,
+                                      const uint8_t *data,
+                                      uint64 len) { }
+
+  // Called when we have an attribute with string data to give to our handler.
+  // The attribute is for the DIE at OFFSET from the beginning of the
+  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
+  // DATA.
+  virtual void ProcessAttributeString(uint64 offset,
+                                      enum DwarfAttribute attr,
+                                      enum DwarfForm form,
+                                      const string& data) { }
+
+  // Called when we have an attribute whose value is the 64-bit signature
+  // of a type unit in the .debug_types section. OFFSET is the offset of
+  // the DIE whose attribute we're reporting. ATTR and FORM are the
+  // attribute's name and form. SIGNATURE is the type unit's signature.
+  virtual void ProcessAttributeSignature(uint64 offset,
+                                         enum DwarfAttribute attr,
+                                         enum DwarfForm form,
+                                         uint64 signature) { }
+
+  // Called when finished processing the DIE at OFFSET.
+  // Because DWARF2/3 specifies a tree of DIEs, you may get starts
+  // before ends of the previous DIE, as we process children before
+  // ending the parent.
+  virtual void EndDIE(uint64 offset) { }
+
+};
+
 // The base of DWARF2/3 debug info is a DIE (Debugging Information
 // Entry.
 // DWARF groups DIE's into a tree and calls the root of this tree a
@@ -225,12 +329,21 @@ class CompilationUnit {
   // Initialize a compilation unit.  This requires a map of sections,
   // the offset of this compilation unit in the .debug_info section, a
   // ByteReader, and a Dwarf2Handler class to call callbacks in.
-  CompilationUnit(const SectionMap& sections, uint64 offset,
+  CompilationUnit(const string& path, const SectionMap& sections, uint64 offset,
                   ByteReader* reader, Dwarf2Handler* handler);
   virtual ~CompilationUnit() {
     if (abbrevs_) delete abbrevs_;
   }
 
+  // Initialize a compilation unit from a .dwo or .dwp file.
+  // In this case, we need the .debug_addr section from the
+  // executable file that contains the corresponding skeleton
+  // compilation unit.  We also inherit the Dwarf2Handler from
+  // the executable file, and call it as if we were still
+  // processing the original compilation unit.
+  void SetSplitDwarf(const uint8_t* addr_buffer, uint64 addr_buffer_length,
+                     uint64 addr_base, uint64 ranges_base, uint64 dwo_id);
+
   // Begin reading a Dwarf2 compilation unit, and calling the
   // callbacks in the Dwarf2Handler
 
@@ -281,6 +394,69 @@ class CompilationUnit {
                                   enum DwarfAttribute attr,
                                   enum DwarfForm form);
 
+  // Called when we have an attribute with unsigned data to give to
+  // our handler.  The attribute is for the DIE at OFFSET from the
+  // beginning of compilation unit, has a name of ATTR, a form of
+  // FORM, and the actual data of the attribute is in DATA.
+  // If we see a DW_AT_GNU_dwo_id attribute, save the value so that
+  // we can find the debug info in a .dwo or .dwp file.
+  void ProcessAttributeUnsigned(uint64 offset,
+                                enum DwarfAttribute attr,
+                                enum DwarfForm form,
+                                uint64 data) {
+    if (attr == DW_AT_GNU_dwo_id)

[ivanpe, 2016/04/27 01:11:44]

I would suggest to put curly braces around these.

[yunlian, 2016/04/27 16:35:29]

Done.

+      dwo_id_ = data;
+     else if (attr == DW_AT_GNU_addr_base)
+      addr_base_ = data;
+    else if (attr == DW_AT_GNU_ranges_base)
+      ranges_base_ = data;
+    // TODO(ccoutant): When we add DW_AT_ranges_base from DWARF-5,

[ivanpe, 2016/04/27 01:11:45]

Why not TODO(yunlian): ?

[yunlian, 2016/04/27 16:35:29]

Done.

+    // that base will apply to DW_AT_ranges attributes in the
+    // skeleton CU as well as in the .dwo/.dwp files.
+    else if (attr == DW_AT_ranges && is_split_dwarf_)
+      data += ranges_base_;
+    handler_->ProcessAttributeUnsigned(offset, attr, form, data);
+  }
+
+  // Called when we have an attribute with signed data to give to
+  // our handler.  The attribute is for the DIE at OFFSET from the
+  // beginning of compilation unit, has a name of ATTR, a form of
+  // FORM, and the actual data of the attribute is in DATA.
+  void ProcessAttributeSigned(uint64 offset,
+                              enum DwarfAttribute attr,
+                              enum DwarfForm form,
+                              int64 data) {
+    handler_->ProcessAttributeSigned(offset, attr, form, data);
+  }
+
+  // Called when we have an attribute with a buffer of data to give to
+  // our handler.  The attribute is for the DIE at OFFSET from the
+  // beginning of compilation unit, has a name of ATTR, a form of
+  // FORM, and the actual data of the attribute is in DATA, and the
+  // length of the buffer is LENGTH.
+  void ProcessAttributeBuffer(uint64 offset,
+                              enum DwarfAttribute attr,
+                              enum DwarfForm form,
+                              const uint8_t* data,
+                              uint64 len) {
+    handler_->ProcessAttributeBuffer(offset, attr, form, data, len);
+  }
+
+  // Called when we have an attribute with string data to give to
+  // our handler.  The attribute is for the DIE at OFFSET from the
+  // beginning of compilation unit, has a name of ATTR, a form of
+  // FORM, and the actual data of the attribute is in DATA.
+  // If we see a DW_AT_GNU_dwo_name attribute, save the value so
+  // that we can find the debug info in a .dwo or .dwp file.
+  void ProcessAttributeString(uint64 offset,
+                              enum DwarfAttribute attr,
+                              enum DwarfForm form,
+                              const char* data) {
+    if (attr == DW_AT_GNU_dwo_name)
+      dwo_name_ = data;
+    handler_->ProcessAttributeString(offset, attr, form, data);
+  }
+
   // Processes all DIEs for this compilation unit
   void ProcessDIEs();
 
@@ -292,6 +468,16 @@ class CompilationUnit {
   // new place to position the stream to.
   const uint8_t *SkipAttribute(const uint8_t *start, enum DwarfForm form);
 
+  // Process the actual debug information in a split DWARF file.
+  void ProcessSplitDwarf();
+
+  // Read the debug sections from a .dwo file.
+  void ReadDebugSectionsFromDwo(ElfReader* elf_reader,
+                                SectionMap* sections);
+
+  // Path of the file containing the debug information.
+  const string path_;
+
   // Offset from section start is the offset of this compilation unit
   // from the beginning of the .debug_info section.
   uint64 offset_from_section_start_;
@@ -322,94 +508,141 @@ class CompilationUnit {
   // ProcessAttribute, which is in the hot path for DWARF2 reading.
   const uint8_t *string_buffer_;
   uint64 string_buffer_length_;
-};
 
-// This class is the main interface between the reader and the
-// client.  The virtual functions inside this get called for
-// interesting events that happen during DWARF2 reading.
-// The default implementation skips everything.
+  // String offsets section buffer and length, if we have a string offsets
+  // section (.debug_str_offsets or .debug_str_offsets.dwo).
+  const uint8_t* str_offsets_buffer_;
+  uint64 str_offsets_buffer_length_;
 
-class Dwarf2Handler {
+  // Address section buffer and length, if we have an address section
+  // (.debug_addr).
+  const uint8_t* addr_buffer_;
+  uint64 addr_buffer_length_;
+
+  // Flag indicating whether this compilation unit is part of a .dwo
+  // or .dwp file.  If true, we are reading this unit because a
+  // skeleton compilation unit in an executable file had a
+  // DW_AT_GNU_dwo_name or DW_AT_GNU_dwo_id attribute.
+  // In a .dwo file, we expect the string offsets section to
+  // have a ".dwo" suffix, and we will use the ".debug_addr" section
+  // associated with the skeleton compilation unit.
+  bool is_split_dwarf_;
+
+  // The value of the DW_AT_GNU_dwo_id attribute, if any.
+  uint64 dwo_id_;
+
+  // The value of the DW_AT_GNU_dwo_name attribute, if any.
+  const char* dwo_name_;
+
+  // If this is a split DWARF CU, the value of the DW_AT_GNU_dwo_id attribute
+  // from the skeleton CU.
+  uint64 skeleton_dwo_id_;
+
+  // The value of the DW_AT_GNU_ranges_base attribute, if any.
+  uint64 ranges_base_;
+
+  // The value of the DW_AT_GNU_addr_base attribute, if any.
+  uint64 addr_base_;
+
+  // True if we have already looked for a .dwp file.
+  bool have_checked_for_dwp_;
+
+  // Path to the .dwp file.
+  string dwp_path_;
+
+  // ByteReader for the DWP file.
+  std::unique_ptr<ByteReader> dwp_byte_reader_;
+
+  // DWP reader.
+   std::unique_ptr<DwpReader> dwp_reader_;
+};
+
+// A Reader for a .dwp file.  Supports the fetching of DWARF debug
+// info for a given dwo_id.
+//
+// There are two versions of .dwp files.  In both versions, the
+// .dwp file is an ELF file containing only debug sections.
+// In Version 1, the file contains many copies of each debug
+// section, one for each .dwo file that is packaged in the .dwp
+// file, and the .debug_cu_index section maps from the dwo_id
+// to a set of section indexes.  In Version 2, the file contains
+// one of each debug section, and the .debug_cu_index section
+// maps from the dwo_id to a set of offsets and lengths that
+// identify each .dwo file's contribution to the larger sections.
+
+class DwpReader {
  public:
-  Dwarf2Handler() { }
+  DwpReader(const ByteReader& byte_reader, ElfReader* elf_reader);
 
-  virtual ~Dwarf2Handler() { }
+  ~DwpReader();
 
-  // Start to process a compilation unit at OFFSET from the beginning of the
-  // .debug_info section. Return false if you would like to skip this
-  // compilation unit.
-  virtual bool StartCompilationUnit(uint64 offset, uint8 address_size,
-                                    uint8 offset_size, uint64 cu_length,
-                                    uint8 dwarf_version) { return false; }
+  // Read the CU index and initialize data members.
+  void Initialize();
 
-  // Start to process a DIE at OFFSET from the beginning of the .debug_info
-  // section. Return false if you would like to skip this DIE.
-  virtual bool StartDIE(uint64 offset, enum DwarfTag tag) { return false; }
+  // Read the debug sections for the given dwo_id.
+  void ReadDebugSectionsForCU(uint64 dwo_id, SectionMap* sections);
 
-  // Called when we have an attribute with unsigned data to give to our
-  // handler. The attribute is for the DIE at OFFSET from the beginning of the
-  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
-  // DATA.
-  virtual void ProcessAttributeUnsigned(uint64 offset,
-                                        enum DwarfAttribute attr,
-                                        enum DwarfForm form,
-                                        uint64 data) { }
+ private:
+  // Search a v1 hash table for "dwo_id".  Returns the slot index
+  // where the dwo_id was found, or -1 if it was not found.
+  int LookupCU(uint64 dwo_id);
 
-  // Called when we have an attribute with signed data to give to our handler.
-  // The attribute is for the DIE at OFFSET from the beginning of the
-  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
-  // DATA.
-  virtual void ProcessAttributeSigned(uint64 offset,
-                                      enum DwarfAttribute attr,
-                                      enum DwarfForm form,
-                                      int64 data) { }
+  // Search a v2 hash table for "dwo_id".  Returns the row index
+  // in the offsets and sizes tables, or 0 if it was not found.
+  uint32 LookupCUv2(uint64 dwo_id);
 
-  // Called when we have an attribute whose value is a reference to
-  // another DIE. The attribute belongs to the DIE at OFFSET from the
-  // beginning of the .debug_info section. Its name is ATTR, its form
-  // is FORM, and the offset of the DIE being referred to from the
-  // beginning of the .debug_info section is DATA.
-  virtual void ProcessAttributeReference(uint64 offset,
-                                         enum DwarfAttribute attr,
-                                         enum DwarfForm form,
-                                         uint64 data) { }
+  // The ELF reader for the .dwp file.
+  ElfReader* elf_reader_;
 
-  // Called when we have an attribute with a buffer of data to give to our
-  // handler. The attribute is for the DIE at OFFSET from the beginning of the
-  // .debug_info section. Its name is ATTR, its form is FORM, DATA points to
-  // the buffer's contents, and its length in bytes is LENGTH. The buffer is
-  // owned by the caller, not the callee, and may not persist for very long.
-  // If you want the data to be available later, it needs to be copied.
-  virtual void ProcessAttributeBuffer(uint64 offset,
-                                      enum DwarfAttribute attr,
-                                      enum DwarfForm form,
-                                      const uint8_t *data,
-                                      uint64 len) { }
+  // The ByteReader for the .dwp file.
+  const ByteReader& byte_reader_;
 
-  // Called when we have an attribute with string data to give to our handler.
-  // The attribute is for the DIE at OFFSET from the beginning of the
-  // .debug_info section. Its name is ATTR, its form is FORM, and its value is
-  // DATA.
-  virtual void ProcessAttributeString(uint64 offset,
-                                      enum DwarfAttribute attr,
-                                      enum DwarfForm form,
-                                      const string& data) { }
+  // Pointer to the .debug_cu_index section.
+  const char* cu_index_;
 
-  // Called when we have an attribute whose value is the 64-bit signature
-  // of a type unit in the .debug_types section. OFFSET is the offset of
-  // the DIE whose attribute we're reporting. ATTR and FORM are the
-  // attribute's name and form. SIGNATURE is the type unit's signature.
-  virtual void ProcessAttributeSignature(uint64 offset,
-                                         enum DwarfAttribute attr,
-                                         enum DwarfForm form,
-                                         uint64 signature) { }
+  // Size of the .debug_cu_index section.
+  size_t cu_index_size_;
 
-  // Called when finished processing the DIE at OFFSET.
-  // Because DWARF2/3 specifies a tree of DIEs, you may get starts
-  // before ends of the previous DIE, as we process children before
-  // ending the parent.
-  virtual void EndDIE(uint64 offset) { }
+  // Pointer to the .debug_str.dwo section.
+  const char* string_buffer_;
+
+  // Size of the .debug_str.dwo section.
+  size_t string_buffer_size_;
+
+  // Version of the .dwp file.  We support versions 1 and 2 currently.
+  int version_;
+
+  // Number of columns in the section tables (version 2).
+  unsigned int ncolumns_;
+
+  // Number of units in the section tables (version 2).
+  unsigned int nunits_;
+
+  // Number of slots in the hash table.
+  unsigned int nslots_;
+
+  // Pointer to the beginning of the hash table.
+  const char* phash_;
+
+  // Pointer to the beginning of the index table.
+  const char* pindex_;
+
+  // Pointer to the beginning of the section index pool (version 1).
+  const char* shndx_pool_;
+
+  // Pointer to the beginning of the section offset table (version 2).
+  const char* offset_table_;
+
+  // Pointer to the beginning of the section size table (version 2).
+  const char* size_table_;
 
+  // Contents of the sections of interest (version 2).
+  const char* abbrev_data_;
+  size_t abbrev_size_;
+  const char* info_data_;
+  size_t info_size_;
+  const char* str_offsets_data_;
+  size_t str_offsets_size_;
 };
 
 // This class is a reader for DWARF's Call Frame Information.  CFI