Re: [PATCH] Fix ptype and print commands for namelist variables(a fortran feature)

[Andrew Burgess <aburgess@redhat.com>]

* Kumar N, Bhuvanendra via Gdb-patches <gdb-patches@sourceware.org> [2022-01-20 16:20:46 +0000]:

> [AMD Official Use Only]
> 
> Hi all,
> 
> Sorry for the delay in sharing the revised patch, I was occupied with some other work. Please find the revised patch with all the details and also patch is inlined below.
> 
> Reason for the assert failure when GDB is built with
> -D_GLIBCXX_DEBUG=1 is, the size or length(TYPE_LENGTH) of the
> namelist variable type was not populated, it was zero, hence assert
> was failing in gdbsupport/array-view.h. Now this is fixed and I
> could test with -D_GLIBCXX_DEBUG=1
> 
> Compiler is not emitting the size of the namelist variable type,
> hence GDB is calculating it. In similar types like
> DW_TAG_structure_type, DW_AT_byte_size attribute is emitted by
> compiler and GDB uses it with TYPE_LENGTH. It's not the case with
> DW_TAG_namelist. Hence size of the namelist variable type is
> calculated in GDB. Also unlike DW_TAG_structure_type, namelist items
> are not allocated in continuous memory, they are spread across,
> hence for each namelist item symbol table lookup is done before
> printing its value. This way making sure namelist items printing is
> intact.

Hi Bhuvan,

Thanks for continuing to work on this feature, and sorry for the slow
turn around on reviews.

I took a look at the changes you made in the latest version, and I
wasn't completely convinced.  Setting the type length seems like a bad
idea, given that these namelists don't have a valid address, and don't
actually live in memory in a contiguous block.  I assume this is why
you ended up adding the change in value.c too.

I think if we just reorder the code in f-valprint.c a little, then we
can avoid the need to compute the type length.  Could you test the
patch below please, and let me know if you see any problems.

This is basically your work with some whitespace clean up in
dwarf2/read.c, the value.c change reverted, and f-valprint.c reworked
a little.  Oh, and I updated the copyright year in the testsuite
files.

Let me know what you think.

Thanks,
Andrew

---

commit 3b365631ef31051210b7ad26463aaccd3501cbfd
Author: Bhuvanendra Kumar N <Bhuvanendra.KumarN@amd.com>
Date:   Wed Feb 2 17:52:27 2022 +0000

    gdb/fortran: support ptype and print commands for namelist variables
    
    Gfortran supports namelists (a Fortran feature); it emits
    DW_TAG_namelist and DW_TAG_namelist_item dies. But gdb does not
    process these dies and does not support 'print' or 'ptype' commands on
    namelist variables.
    
    An attempt to print namelist variables results in gdb bailing out with
    the error message as shown below.
    
      (gdb) print nml
      No symbol "nml" in current context.
    
    This commit is to make the print and ptype commands work for namelist
    variables and its items. Sample output of these commands is shared
    below, with fixed gdb.
    
      (gdb) ptype nml
      type = Type nml
          integer(kind=4) :: a
          integer(kind=4) :: b
      End Type nml
      (gdb) print nml
      $1 = ( a = 10, b = 20 )

diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 1a749eac334..056ba97ee91 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -9694,6 +9694,7 @@ process_die (struct die_info *die, struct dwarf2_cu *cu)
     case DW_TAG_interface_type:
     case DW_TAG_structure_type:
     case DW_TAG_union_type:
+    case DW_TAG_namelist:
       process_structure_scope (die, cu);
       break;
     case DW_TAG_enumeration_type:
@@ -14556,8 +14557,21 @@ dwarf2_add_field (struct field_info *fip, struct die_info *die,
 
   fp = &new_field->field;
 
-  if (die->tag == DW_TAG_member && ! die_is_declaration (die, cu))
-    {
+  if ((die->tag == DW_TAG_member || die->tag == DW_TAG_namelist_item)
+      && !die_is_declaration (die, cu))
+    {
+      if (die->tag == DW_TAG_namelist_item)
+        {
+	  /* Typically, DW_TAG_namelist_item are references to namelist items.
+	     If so, follow that reference.  */
+	  struct attribute *attr1 = dwarf2_attr (die, DW_AT_namelist_item, cu);
+	  struct die_info *item_die = nullptr;
+	  struct dwarf2_cu *item_cu = cu;
+          if (attr1->form_is_ref ())
+	    item_die = follow_die_ref (die, attr1, &item_cu);
+	  if (item_die != nullptr)
+	    die = item_die;
+        }
       /* Data member other than a C++ static data member.  */
 
       /* Get type of field.  */
@@ -15615,6 +15629,10 @@ read_structure_type (struct die_info *die, struct dwarf2_cu *cu)
     {
       type->set_code (TYPE_CODE_UNION);
     }
+  else if (die->tag == DW_TAG_namelist)
+    {
+      type->set_code (TYPE_CODE_NAMELIST);
+    }
   else
     {
       type->set_code (TYPE_CODE_STRUCT);
@@ -15817,7 +15835,8 @@ handle_struct_member_die (struct die_info *child_die, struct type *type,
 			  struct dwarf2_cu *cu)
 {
   if (child_die->tag == DW_TAG_member
-      || child_die->tag == DW_TAG_variable)
+      || child_die->tag == DW_TAG_variable
+      || child_die->tag == DW_TAG_namelist_item)
     {
       /* NOTE: carlton/2002-11-05: A C++ static data member
 	 should be a DW_TAG_member that is a declaration, but
@@ -15860,8 +15879,10 @@ handle_struct_member_die (struct die_info *child_die, struct type *type,
     handle_variant (child_die, type, fi, template_args, cu);
 }
 
-/* Finish creating a structure or union type, including filling in
-   its members and creating a symbol for it.  */
+/* Finish creating a structure or union type, including filling in its
+   members and creating a symbol for it. This function also handles Fortran
+   namelist variables, their items or members and creating a symbol for
+   them.  */
 
 static void
 process_structure_scope (struct die_info *die, struct dwarf2_cu *cu)
@@ -21963,9 +21984,17 @@ new_symbol (struct die_info *die, struct type *type, struct dwarf2_cu *cu,
 	case DW_TAG_union_type:
 	case DW_TAG_set_type:
 	case DW_TAG_enumeration_type:
-	  SYMBOL_ACLASS_INDEX (sym) = LOC_TYPEDEF;
-	  SYMBOL_DOMAIN (sym) = STRUCT_DOMAIN;
-
+	case DW_TAG_namelist:
+	  if (die->tag == DW_TAG_namelist)
+	    {
+	      SYMBOL_ACLASS_INDEX (sym) = LOC_STATIC;
+	      SYMBOL_DOMAIN (sym) = VAR_DOMAIN;
+	    }
+	  else
+	    {
+	      SYMBOL_ACLASS_INDEX (sym) = LOC_TYPEDEF;
+	      SYMBOL_DOMAIN (sym) = STRUCT_DOMAIN;
+	    }
 	  {
 	    /* NOTE: carlton/2003-11-10: C++ class symbols shouldn't
 	       really ever be static objects: otherwise, if you try
@@ -22902,6 +22931,7 @@ dwarf2_name (struct die_info *die, struct dwarf2_cu *cu)
       && die->tag != DW_TAG_class_type
       && die->tag != DW_TAG_interface_type
       && die->tag != DW_TAG_structure_type
+      && die->tag != DW_TAG_namelist
       && die->tag != DW_TAG_union_type)
     return NULL;
 
@@ -22926,6 +22956,7 @@ dwarf2_name (struct die_info *die, struct dwarf2_cu *cu)
     case DW_TAG_interface_type:
     case DW_TAG_structure_type:
     case DW_TAG_union_type:
+    case DW_TAG_namelist:
       /* Some GCC versions emit spurious DW_AT_name attributes for unnamed
 	 structures or unions.  These were of the form "._%d" in GCC 4.1,
 	 or simply "<anonymous struct>" or "<anonymous union>" in GCC 4.3
diff --git a/gdb/f-typeprint.c b/gdb/f-typeprint.c
index 6fd3d519c86..3b26bf74b61 100644
--- a/gdb/f-typeprint.c
+++ b/gdb/f-typeprint.c
@@ -121,6 +121,7 @@ f_language::f_type_print_varspec_prefix (struct type *type,
     case TYPE_CODE_UNDEF:
     case TYPE_CODE_STRUCT:
     case TYPE_CODE_UNION:
+    case TYPE_CODE_NAMELIST:
     case TYPE_CODE_ENUM:
     case TYPE_CODE_INT:
     case TYPE_CODE_FLT:
@@ -261,6 +262,7 @@ f_language::f_type_print_varspec_suffix (struct type *type,
     case TYPE_CODE_UNDEF:
     case TYPE_CODE_STRUCT:
     case TYPE_CODE_UNION:
+    case TYPE_CODE_NAMELIST:
     case TYPE_CODE_ENUM:
     case TYPE_CODE_INT:
     case TYPE_CODE_FLT:
@@ -305,7 +307,8 @@ f_language::f_type_print_base (struct type *type, struct ui_file *stream,
       const char *prefix = "";
       if (type->code () == TYPE_CODE_UNION)
 	prefix = "Type, C_Union :: ";
-      else if (type->code () == TYPE_CODE_STRUCT)
+      else if (type->code () == TYPE_CODE_STRUCT
+               || type->code () == TYPE_CODE_NAMELIST)
 	prefix = "Type ";
       fprintf_filtered (stream, "%*s%s%s", level, "", prefix, type->name ());
       return;
@@ -391,6 +394,7 @@ f_language::f_type_print_base (struct type *type, struct ui_file *stream,
 
     case TYPE_CODE_STRUCT:
     case TYPE_CODE_UNION:
+    case TYPE_CODE_NAMELIST:
       if (type->code () == TYPE_CODE_UNION)
 	fprintf_filtered (stream, "%*sType, C_Union :: ", level, "");
       else
diff --git a/gdb/f-valprint.c b/gdb/f-valprint.c
index 3d13eb11fb0..10dfcaf7c41 100644
--- a/gdb/f-valprint.c
+++ b/gdb/f-valprint.c
@@ -512,24 +512,38 @@ f_language::value_print_inner (struct value *val, struct ui_file *stream,
 
     case TYPE_CODE_STRUCT:
     case TYPE_CODE_UNION:
+    case TYPE_CODE_NAMELIST:
       /* Starting from the Fortran 90 standard, Fortran supports derived
 	 types.  */
       fprintf_filtered (stream, "( ");
       for (index = 0; index < type->num_fields (); index++)
 	{
-	  struct value *field = value_field (val, index);
-
-	  struct type *field_type = check_typedef (type->field (index).type ());
-
+	  struct type *field_type
+	    = check_typedef (type->field (index).type ());
 
 	  if (field_type->code () != TYPE_CODE_FUNC)
 	    {
-	      const char *field_name;
+	      const char *field_name = type->field (index).name ();
+	      struct value *field;
+
+	      if (type->code () == TYPE_CODE_NAMELIST)
+		{
+		  /* While printing namelist items, fetch the appropriate
+		     value field before printing its value.  */
+		  struct block_symbol sym
+		    = lookup_symbol (field_name, get_selected_block (nullptr),
+				     VAR_DOMAIN, nullptr);
+		  if (sym.symbol == nullptr)
+		    error (_("failed to find symbol for name list component %s"),
+			   field_name);
+		  field = value_of_variable (sym.symbol, sym.block);
+		}
+	      else
+		field = value_field (val, index);
 
 	      if (printed_field > 0)
 		fputs_filtered (", ", stream);
 
-	      field_name = type->field (index).name ();
 	      if (field_name != NULL)
 		{
 		  fputs_styled (field_name, variable_name_style.style (),
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index 7238873e4db..5072dc24bfa 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -196,6 +196,19 @@ enum type_code
 
     /* * Fixed Point type.  */
     TYPE_CODE_FIXED_POINT,
+
+    /* * Fortran namelist is a group of variables or arrays that can be
+       read or written.
+
+       Namelist syntax: NAMELIST / groupname / namelist_items ...
+       NAMELIST statement assign a group name to a collection of variables
+       called as namelist items. The namelist items can be of any data type
+       and can be variables or arrays.
+
+       Compiler emit DW_TAG_namelist for group name and DW_TAG_namelist_item
+       for each of the namelist items. GDB process these namelist dies
+       and print namelist variables during print and ptype commands.  */
+    TYPE_CODE_NAMELIST,
   };
 
 /* * Some bits for the type's instance_flags word.  See the macros
diff --git a/gdb/testsuite/gdb.fortran/namelist.exp b/gdb/testsuite/gdb.fortran/namelist.exp
new file mode 100644
index 00000000000..d6263e12fec
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/namelist.exp
@@ -0,0 +1,50 @@
+# Copyright (C) 2021-2022 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# This file is part of the gdb testsuite.  It contains tests for fortran
+# namelist.
+
+if { [skip_fortran_tests] } { return -1 }
+
+standard_testfile .f90
+load_lib "fortran.exp"
+
+if {[prepare_for_testing "failed to prepare" $testfile $srcfile {debug f90}]} {
+    return -1
+}
+
+if ![fortran_runto_main] then {
+    perror "couldn't run to main"
+    continue
+}
+
+# Depending on the compiler being used, the type names can be printed
+# differently.
+set int [fortran_int4]
+
+gdb_breakpoint [gdb_get_line_number "Display namelist"]
+gdb_continue_to_breakpoint "Display namelist"
+
+if {[test_compiler_info {gcc-*}]} {
+    gdb_test "ptype nml" \
+        "type = Type nml\r\n *$int :: a\r\n *$int :: b\r\n *End Type nml"
+    gdb_test "print nml" \
+        "\\$\[0-9\]+ = \\( a = 10, b = 20 \\)"
+} else {
+    gdb_test "ptype nml" \
+        "No symbol \"nml\" in current context\\."
+    gdb_test "print nml" \
+        "No symbol \"nml\" in current context\\."
+}
diff --git a/gdb/testsuite/gdb.fortran/namelist.f90 b/gdb/testsuite/gdb.fortran/namelist.f90
new file mode 100644
index 00000000000..9e2ba0489d2
--- /dev/null
+++ b/gdb/testsuite/gdb.fortran/namelist.f90
@@ -0,0 +1,27 @@
+! Copyright (C) 2021-2022 Free Software Foundation, Inc.
+!
+! This program is free software; you can redistribute it and/or modify
+! it under the terms of the GNU General Public License as published by
+! the Free Software Foundation; either version 3 of the License, or
+! (at your option) any later version.
+!
+! This program is distributed in the hope that it will be useful,
+! but WITHOUT ANY WARRANTY; without even the implied warranty of
+! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+! GNU General Public License for more details.
+!
+! You should have received a copy of the GNU General Public License
+! along with this program.  If not, see <http://www.gnu.org/licenses/>.
+!
+! This file is the Fortran source file for namelist.exp.
+
+program main
+
+  integer :: a, b
+  namelist /nml/ a, b
+
+  a = 10
+  b = 20
+  Write(*,nml) ! Display namelist
+
+end program main
diff --git a/include/dwarf2.def b/include/dwarf2.def
index 4214c80907a..530c6f849f9 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -289,7 +289,7 @@ DW_AT (DW_AT_frame_base, 0x40)
 DW_AT (DW_AT_friend, 0x41)
 DW_AT (DW_AT_identifier_case, 0x42)
 DW_AT (DW_AT_macro_info, 0x43)
-DW_AT (DW_AT_namelist_items, 0x44)
+DW_AT (DW_AT_namelist_item, 0x44)
 DW_AT (DW_AT_priority, 0x45)
 DW_AT (DW_AT_segment, 0x46)
 DW_AT (DW_AT_specification, 0x47)