Add PROP_VARIABLE_NAME

With -fgnat-encodings=minimal, an internal version (these patches will
be upstreamed in the near future) of the Ada compiler can emit DWARF
for an array where the bound comes from a variable, like:

 <1><12a7>: Abbrev Number: 7 (DW_TAG_array_type)
    <12a8>   DW_AT_name        : (indirect string, offset: 0x1ae9): pck__my_array
[...]
 <2><12b4>: Abbrev Number: 8 (DW_TAG_subrange_type)
    <12b5>   DW_AT_type        : <0x1294>
    <12b9>   DW_AT_upper_bound : <0x1277>

With the upper bound DIE being:

 <1><1277>: Abbrev Number: 2 (DW_TAG_variable)
    <1278>   DW_AT_name        : (indirect string, offset: 0x1a4d): pck__my_length___U
    <127c>   DW_AT_type        : <0x128f>
    <1280>   DW_AT_external    : 1
    <1280>   DW_AT_artificial  : 1
    <1280>   DW_AT_declaration : 1

Note that the variable is just a declaration -- in this situation, the
variable comes from another compilation unit, and must be found when
trying to compute the array bound.

This patch adds a new PROP_VARIABLE_NAME kind, to enable this search.

This same scenario can occur with DW_OP_GNU_variable_value, so this
patch adds support for that as well.

gdb/ChangeLog
2021-06-04  Tom Tromey  <tromey@adacore.com>

	* dwarf2/read.h (dwarf2_fetch_die_type_sect_off): Add 'var_name'
	parameter.
	* dwarf2/loc.c (dwarf2_evaluate_property) <case
	PROP_VARIABLE_NAME>: New case.
	(compute_var_value): New function.
	(sect_variable_value): Use compute_var_value.
	* dwarf2/read.c (attr_to_dynamic_prop): Handle DW_TAG_variable.
	(var_decl_name): New function.
	(dwarf2_fetch_die_type_sect_off): Add 'var_name' parameter.
	* gdbtypes.h (enum dynamic_prop_kind) <PROP_VARIABLE_NAME>: New
	constant.
	(union dynamic_prop_data) <variable_name>: New member.
	(struct dynamic_prop) <variable_name, set_variable_name>: New
	methods.

gdb/testsuite/ChangeLog
2021-06-04  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/array_of_symbolic_length.exp: New file.
	* gdb.ada/array_of_symbolic_length/foo.adb: New file.
	* gdb.ada/array_of_symbolic_length/gl.adb: New file.
	* gdb.ada/array_of_symbolic_length/gl.ads: New file.
	* gdb.ada/array_of_symbolic_length/pck.adb: New file.
	* gdb.ada/array_of_symbolic_length/pck.ads: New file.

1 files changed, 22 insertions, 0 deletions

diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index bb4d26e..0cc00e7 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -388,6 +388,7 @@ enum dynamic_prop_kind
   PROP_LOCLIST,    /* Location list.  */
   PROP_VARIANT_PARTS, /* Variant parts.  */
   PROP_TYPE,	   /* Type.  */
+  PROP_VARIABLE_NAME, /* Variable name.  */
 };
 
 union dynamic_prop_data
@@ -414,6 +415,11 @@ union dynamic_prop_data
      rewrite the property's kind and set this field.  */
 
   struct type *original_type;
+
+  /* Name of a variable to look up; the variable holds the value of
+     this property.  */
+
+  const char *variable_name;
 };
 
 /* * Used to store a dynamic property.  */
@@ -496,6 +502,22 @@ struct dynamic_prop
     m_data.original_type = original_type;
   }
 
+  /* Return the name of the variable that holds this property's value.
+     Only valid for PROP_VARIABLE_NAME.  */
+  const char *variable_name () const
+  {
+    gdb_assert (m_kind == PROP_VARIABLE_NAME);
+    return m_data.variable_name;
+  }
+
+  /* Set the name of the variable that holds this property's value,
+     and set this property to be of kind PROP_VARIABLE_NAME.  */
+  void set_variable_name (const char *name)
+  {
+    m_kind = PROP_VARIABLE_NAME;
+    m_data.variable_name = name;
+  }
+
   /* Determine which field of the union dynamic_prop.data is used.  */
   enum dynamic_prop_kind m_kind;