DWARF v5: fix directory index in the line table

[MaskRay]

Summary

Prior to DWARF v5, a directory index of 0 represents DW_AT_comp_dir.

In DWARF v5, the index starts with 0 and Entry.DirIdx is the index into
Prologue.IncludeDirectories.

[MaskRay]

Ping 😊

[labath]

I believe the changes here are correct. What I find unfortunate is that it is not able to test this without including a debug_info info section in the object file. Which is a bit ironic given that the purpose of these changes in DWARF5 was to have a fully-standalone .debug_line section.

[MaskRay]

In D61253#1491551, @labath wrote:

I believe the changes here are correct. What I find unfortunate is that it is not able to test this without including a debug_info info section in the object file. Which is a bit ironic given that the purpose of these changes in DWARF5 was to have a fully-standalone .debug_line section.

The .debug_info is used by llvm-symbolizer to locate the compile unit. Without it llvm-symbolizer doesn't bother reading .debug_line...

[dblaikie]

In D61253#1491601, @MaskRay wrote:

In D61253#1491551, @labath wrote:

I believe the changes here are correct. What I find unfortunate is that it is not able to test this without including a debug_info info section in the object file. Which is a bit ironic given that the purpose of these changes in DWARF5 was to have a fully-standalone .debug_line section.

The .debug_info is used by llvm-symbolizer to locate the compile unit. Without it llvm-symbolizer doesn't bother reading .debug_line...

Right - Pavel's point is that DWARFv5 line tables can/should be readable without debug_info, so it's unfortunate that llvm-symbolizer still reads debug_info when parsing a DWARFv5 line table, when it shouldn't have to.

lib/DebugInfo/DWARF/DWARFDebugLine.cpp

bool DWARFDebugLine::LineTable::getFileNameByIndex(uint64_t FileIndex,
   StringRef FileName = Entry.Name.getAsCString().getValue();
   if (Kind != FileLineInfoKind::AbsoluteFilePath ||
       isPathAbsoluteOnWindowsOrPosix(FileName)) {
     Result = FileName;
     return true;
   }
 
   SmallString<16> FilePath;
-  uint64_t IncludeDirIndex = Entry.DirIdx;
   StringRef IncludeDir;
   // Be defensive about the contents of Entry.
-  if (IncludeDirIndex > 0 &&
-      IncludeDirIndex <= Prologue.IncludeDirectories.size())
-    IncludeDir = Prologue.IncludeDirectories[IncludeDirIndex - 1]
+  if (Prologue.getVersion() >= 5) {
+    if (Entry.DirIdx < Prologue.IncludeDirectories.size())
+      IncludeDir =
+          Prologue.IncludeDirectories[Entry.DirIdx].getAsCString().getValue();
+  } else {
+    if (0 < Entry.DirIdx && Entry.DirIdx <= Prologue.IncludeDirectories.size())
+      IncludeDir = Prologue.IncludeDirectories[Entry.DirIdx - 1]
                        .getAsCString()
                        .getValue();
 
     // We may still need to append compilation directory of compile unit.
     // We know that FileName is not absolute, the only way to have an
     // absolute path at this point would be if IncludeDir is absolute.
     if (CompDir && !isPathAbsoluteOnWindowsOrPosix(IncludeDir))
       sys::path::append(FilePath, CompDir);
+  }
 
   // sys::path::append skips empty strings.
   sys::path::append(FilePath, IncludeDir, FileName);
   Result = FilePath.str();
   return true;
 }
 
 bool DWARFDebugLine::LineTable::getFileLineInfoForAddress(

test/DebugInfo/symbolize-directory.s

+# REQUIRES: x86-registered-target
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64 -dwarf-version=5 %s -o %t.o
+# RUN: llvm-symbolizer --obj=%t.o --functions=none 0 1 | FileCheck %s
+
+# CHECK: /home/0.cc:1:0
+# CHECK: /tmp/1.cc:2:1
+
+.Lfunc_begin0:
+  .file 0 "/home" "0.cc"
+  .file 1 "/tmp" "1.cc"
+  .loc 0 1 0                 # 0.cc:1:0
+  nop
+  .loc 1 2 1                 # 1.cc:2:1
+  nop
+  .loc 0 1 1 prologue_end    # 0.cc:1:1
+.Lfunc_end0:
+
+.section .debug_abbrev,"",@progbits
+  .byte 1     # Abbreviation Code
+  .byte 17    # DW_TAG_compile_unit
+  .byte 1     # DW_children_yes
+  .byte 16    # DW_AT_stmt_list
+  .byte 23    # DW_FROM_sec_offset
+  .byte 17    # DW_AT_low_pc
+  .byte 1     # DW_FORM_addr
+  .byte 18    # DW_AT_high_pc
+  .byte 6     # DW_FORM_data4
+  .byte 0     # EOM(1)
+  .byte 0     # EOM(2)
+
+  .byte 2     # Abbreviation Code
+  .byte 46    # DW_TAG_subprogram
+  .byte 0     # DW_children_no
+  .byte 3     # DW_AT_name
+  .byte 8     # DW_FORM_string
+  .byte 17    # DW_AT_low_pc
+  .byte 1     # DW_FORM_addr
+  .byte 18    # DW_AT_high_pc
+  .byte 6     # DW_FORM_data4
+  .byte 0     # EOM(1)
+  .byte 0     # EOM(2)
+
+  .byte 0     # EOM(3)
+
+.section .debug_info,"",@progbits
+.Lcu_begin0:
+  .long .Lcu_end0-.Lcu_begin0-4 # Length of Unit
+  .short 5                      # DWARF version number
+  .byte 1                       # DWARF Unit Type
+  .byte 8                       # Address Size (in bytes)
+  .long .debug_abbrev           # Offset Into Abbrev.
+  .byte 1                       # Abbrev [1]
+  .long 0                       # DW_AT_stmt_list
+  .quad 0                       # DW_AT_low_pc
+  .long 2                       # DW_AT_high_pc
+  .byte 2                       # Abbrev [2] DW_TAG_subprogram
+  .asciz "0.c"                  # DW_AT_name
+  .quad 0                       # DW_AT_low_pc
+  .long 2                       # DW_AT_high_pc
+  .byte 0
+.Lcu_end0: