[DWARF parser] Add basic support for DWZ DWARF multifile extensions.

This change implements basic support for DWARF alternate sections
proposal: http://www.dwarfstd.org/ShowIssue.php?issue=120604.1&type=open

LLVM tools now understand new forms: DW_FORM_GNU_ref_alt and
DW_FORM_GNU_strp_alt, which are used as references to .debug_info and
.debug_str sections respectively, stored in a separate file, and
possibly shared between different executables / shared objects.

llvm-dwarfdump and llvm-symbolizer don't yet know how to access this
alternate debug file (usually pointed by .gnu_debugaltlink section),
but they can at lease properly parse and dump regular files, which
refer to it.

This change should fix crashes of llvm-dwarfdump and llvm-symbolizer on
files produced by running "dwz" tool. Such files are already installed
on some modern Linux distributions.

llvm-svn: 237721

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/Support/Dwarf.cpp b/llvm/lib/Support/Dwarf.cpp
index 95c4bc32701..6229825a8ee 100644
--- a/llvm/lib/Support/Dwarf.cpp
+++ b/llvm/lib/Support/Dwarf.cpp
@@ -233,6 +233,10 @@ const char *llvm::dwarf::FormEncodingString(unsigned Encoding) {
     // DWARF5 Fission Extension Forms
   case DW_FORM_GNU_addr_index:           return "DW_FORM_GNU_addr_index";
   case DW_FORM_GNU_str_index:            return "DW_FORM_GNU_str_index";
+
+  // Alternate debug sections proposal (output of "dwz" tool).
+  case DW_FORM_GNU_ref_alt:              return "DW_FORM_GNU_ref_alt";
+  case DW_FORM_GNU_strp_alt:             return "DW_FORM_GNU_strp_alt";
   }
   return nullptr;
 }