[PATCH] PR debug/90981 Empty .debug_addr crashes -gdwarf-5 -gsplit-dwarf

[Mark Wielaard]

Even if there was no, or an empty address list we would try to generate
and index for the .debug_addr section with -gdwarf-5 and -gsplit-dwarf.
The skeleton DIE would also get a (dangling) DW_AT_addr_base in that case.

	PR debug/90981
	* dwarf2out.c (add_top_level_skeleton_die_attrs): Only add
	DW_AT_addr_base if there is actually a .debug_addr section with
	addresses.
	(output_addr_table): Add DWARF5 table index generation here after
	checking there are actually any addresses from...
	(dwarf2out_finish): ...here.
	* testsuite/g++.dg/pr90981.C: New test.
---
diff --git a/gcc/dwarf2out.c b/gcc/dwarf2out.c
index 7fa8b05..c3c2dbc 100644
--- a/gcc/dwarf2out.c
+++ b/gcc/dwarf2out.c
@@ -11196,7 +11196,8 @@ add_top_level_skeleton_die_attrs (dw_die_ref die)
   if (comp_dir != NULL)
     add_skeleton_AT_string (die, DW_AT_comp_dir, comp_dir);
   add_AT_pubnames (die);
-  add_AT_lineptr (die, dwarf_AT (DW_AT_addr_base), debug_addr_section_label);
+  if (addr_index_table != NULL && addr_index_table->size () > 0)
+    add_AT_lineptr (die, dwarf_AT (DW_AT_addr_base), debug_addr_section_label);
 }
 
 /* Output skeleton debug sections that point to the dwo file.  */
@@ -29108,6 +29109,30 @@ output_addr_table (void)
     return;
 
   switch_to_section (debug_addr_section);
+  /* GNU DebugFission https://gcc.gnu.org/wiki/DebugFission
+     which GCC uses to implement -gsplit-dwarf as DWARF GNU extension
+     before DWARF5, didn't have a header for .debug_addr units.
+     DWARF5 specifies a small header when address tables are used.  */
+  if (dwarf_version >= 5)
+    {
+      unsigned int last_idx = 0;
+      unsigned long addrs_length;
+
+      addr_index_table->traverse_noresize
+	<unsigned int *, count_index_addrs> (&last_idx);
+      addrs_length = last_idx * DWARF2_ADDR_SIZE + 4;
+
+      if (DWARF_INITIAL_LENGTH_SIZE - DWARF_OFFSET_SIZE == 4)
+	dw2_asm_output_data (4, 0xffffffff,
+			     "Escape value for 64-bit DWARF extension");
+      dw2_asm_output_data (DWARF_OFFSET_SIZE, addrs_length,
+			   "Length of Address Unit");
+      dw2_asm_output_data (2, 5, "DWARF addr version");
+      dw2_asm_output_data (1, DWARF2_ADDR_SIZE, "Size of Address");
+      dw2_asm_output_data (1, 0, "Size of Segment Descriptor");
+    }
+  ASM_OUTPUT_LABEL (asm_out_file, debug_addr_section_label);
+
   addr_index_table
     ->traverse_noresize<unsigned int *, output_addr_table_entry> (&index);
 }
@@ -31630,30 +31655,6 @@ dwarf2out_finish (const char *filename)
 			    ranges_section_label);
 	}
 
-      switch_to_section (debug_addr_section);
-      /* GNU DebugFission https://gcc.gnu.org/wiki/DebugFission
-	 which GCC uses to implement -gsplit-dwarf as DWARF GNU extension
-	 before DWARF5, didn't have a header for .debug_addr units.
-	 DWARF5 specifies a small header when address tables are used.  */
-      if (dwarf_version >= 5)
-	{
-	  unsigned int last_idx = 0;
-	  unsigned long addrs_length;
-
-	  addr_index_table->traverse_noresize
-	    <unsigned int *, count_index_addrs> (&last_idx);
-	  addrs_length = last_idx * DWARF2_ADDR_SIZE + 4;
-
-	  if (DWARF_INITIAL_LENGTH_SIZE - DWARF_OFFSET_SIZE == 4)
-	    dw2_asm_output_data (4, 0xffffffff,
-				 "Escape value for 64-bit DWARF extension");
-	  dw2_asm_output_data (DWARF_OFFSET_SIZE, addrs_length,
-			       "Length of Address Unit");
-	  dw2_asm_output_data (2, 5, "DWARF addr version");
-	  dw2_asm_output_data (1, DWARF2_ADDR_SIZE, "Size of Address");
-	  dw2_asm_output_data (1, 0, "Size of Segment Descriptor");
-	}
-      ASM_OUTPUT_LABEL (asm_out_file, debug_addr_section_label);
       output_addr_table ();
     }
 
diff --git a/gcc/testsuite/g++.dg/pr90981.C b/gcc/testsuite/g++.dg/pr90981.C
new file mode 100644
index 0000000..4ae871e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr90981.C
@@ -0,0 +1,8 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -g -gdwarf-5 -gsplit-dwarf" } */
+
+/* No addresses in the DWARF, so no .debug_addr section,
+   don't crash trying to generate an addr table index anyway.  */
+
+namespace { struct t {}; }
+t f () { return t (); }
-- 
1.8.3.1