[binutils-gdb] dwarf2: avoid decoding .debug_line for type units

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=8f583ac13920391c22e864f9aa6487379edb3995

commit 8f583ac13920391c22e864f9aa6487379edb3995
Author: Bratislav Filipovic <[email protected]>
Date:   Thu Apr 23 16:17:20 2026 +0000

    dwarf2: avoid decoding .debug_line for type units
    
    Running gdb.dwarf2/pr13961.exp with clang fails with an internal error:
    
      gdb/dwarf2/read.c: internal-error: decode_line_header_for_cu:
      Assertion `!cu->per_cu->is_debug_types ()' failed.
    
    pr13961 is a legacy .S test that references a .debug_line label from
    both a CU and a TU.  The assembly includes an empty .debug_line section
    declaration:
    
      .section .debug_line,"",%progbits
    .Ldebug_line0:
    
    With gcc this results in a dummy (valid, but content-less) .debug_line
    header being emitted, so GDB can build a line header and resolve file
    indices.  With clang the .debug_line section can be missing/empty,
    leaving the line header unset.
    
    During symbol creation, new_symbol may then try to lazily decode the
    CU-only line header while processing a type unit, which triggers the
    assertion above.
    
    Fix this by only decoding the line header for non-type units.  If no
    line header is available, emit a complaint and continue without setting
    the symtab rather than attempting CU-only line decoding from a TU.
    
    Tested: gdb.dwarf2/pr13961.exp (CC_FOR_TARGET=clang-23)

Diff:
---
 gdb/dwarf2/read.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index bc7b8b46d87..890a36809f7 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -15452,16 +15452,28 @@ new_symbol_file_line (struct die_info *die, struct dwarf2_cu *cu,
   if (!index_cst.has_value ())
     return;
 
-  if (file_cu->line_header == nullptr)
+  /* decode_line_header_for_cu is CU-only and asserts on type units.
+     For type units, the line header setup runs before processing child
+     DIEs, in method dwarf2_cu::setup_type_unit_groups.  So if
+     line_header is still nullptr here it means there is no usable line
+     table for this unit.  */
+  if (file_cu->line_header == nullptr
+      && !file_cu->per_cu->is_debug_types ())
     {
       file_and_directory fnd (nullptr, nullptr);
       decode_line_header_for_cu (file_cu->dies, file_cu, fnd);
     }
 
   file_name_index file_index = (file_name_index) *index_cst;
-  struct file_entry *fe = nullptr;
-  if (file_cu->line_header != nullptr)
-    fe = file_cu->line_header->file_name_at (file_index);
+
+  /* Check if we successfully got line_header.  */
+  if (file_cu->line_header == nullptr)
+    {
+      complaint (_("missing .debug_line information to resolve file index"));
+      return;
+    }
+
+  struct file_entry *fe = file_cu->line_header->file_name_at (file_index);
 
   if (fe == nullptr)
     {