Only generate dwarf entries if the line & column looks legitimate (#632)

backend/debug/dwarf/dwarf_high/dwarf_attribute_helpers.ml

@@ -112,6 +112,10 @@ let create_external ~is_visible_externally =
     let spec = AS.create External Flag in
     AV.create spec (V.bool ~comment:"not visible externally" false)
 
+let create_artificial () =
+  let spec = AS.create Artificial Flag_present in
+  AV.create spec (V.flag_true ~comment:"artificial" ())
+
 let create_decl_file file =
   let spec = AS.create Decl_file Udata in
   let file = Uint64.of_nonnegative_int_exn file in

backend/debug/dwarf/dwarf_high/dwarf_attribute_helpers.mli

@@ -55,6 +55,8 @@ val create_stmt_list :
 val create_external :
   is_visible_externally:bool -> Dwarf_attribute_values.Attribute_value.t
 
+val create_artificial : unit -> Dwarf_attribute_values.Attribute_value.t
+
 val create_decl_file : int -> Dwarf_attribute_values.Attribute_value.t
 
 val create_decl_line : int -> Dwarf_attribute_values.Attribute_value.t

backend/debug/dwarf/dwarf_ocaml/dwarf_concrete_instances.ml

@@ -37,28 +37,33 @@ let for_fundecl ~get_file_id state fundecl =
   in
   let start_sym = Asm_symbol.create fun_name in
   let end_sym = Asm_symbol.create (end_symbol_name ~start_symbol:fun_name) in
-  let file_num, line, startchar =
+  let location_attributes =
     let loc = Debuginfo.to_location fundecl.fun_dbg in
     if Location.is_none loc
-    then 0, 0, 0
+    then [DAH.create_artificial ()]
     else
       let file, line, startchar = Location.get_pos_info loc.loc_start in
-      get_file_id file, line, startchar
+      let attributes = [DAH.create_decl_file (get_file_id file)] in
+      if line < 0 then attributes
+      else if startchar < 0 then (DAH.create_decl_line line) :: attributes
+      else (* Both line and startchar are >= 0*)
+        (DAH.create_decl_line line) :: (DAH.create_decl_column startchar)
+        :: attributes
+  in
+  let attribute_values =
+    location_attributes @
+    [ DAH.create_name fun_name;
+      DAH.create_linkage_name ~linkage_name;
+      DAH.create_low_pc_from_symbol start_sym;
+      DAH.create_high_pc_from_symbol ~low_pc:start_sym end_sym;
+      DAH.create_entry_pc_from_symbol start_sym;
+      DAH.create_stmt_list
+        ~debug_line_label:
+          (Asm_label.for_dwarf_section Asm_section.Debug_line) ]
   in
   let concrete_instance_proto_die =
     Proto_die.create ~parent:(Some parent) ~tag:Subprogram
-      ~attribute_values:
-        [ DAH.create_name fun_name;
-          DAH.create_linkage_name ~linkage_name;
-          DAH.create_low_pc_from_symbol start_sym;
-          DAH.create_high_pc_from_symbol ~low_pc:start_sym end_sym;
-          DAH.create_entry_pc_from_symbol start_sym;
-          DAH.create_decl_file file_num;
-          DAH.create_decl_line line;
-          DAH.create_decl_column startchar;
-          DAH.create_stmt_list
-            ~debug_line_label:
-              (Asm_label.for_dwarf_section Asm_section.Debug_line) ]
+      ~attribute_values
       ()
   in
   let name = Printf.sprintf "__concrete_instance_%s" fun_name in