Re: Support constants for DW_AT_data_member_location

[Jim Blandy <jimb@codesourcery.com>]

Vladimir Prus <vladimir at codesourcery.com> writes:
> DWARF standard allows DW_AT_data_member_location value
> to be a plain constant, but GDB does not. Is the following OK?

A constant can have other FORMs, too; how about this?

gdb/ChangeLog:
2007-11-29  Jim Blandy  <jimb@codesourcery.com>

	* dwarf2read.c (dwarf2_attr_is_constant): New function.
	(dwarf2_add_field): Use it to recognize DW_AT_data_member_location
	attributes with constant values; use
	dwarf2_get_attr_constant_value to get said values.

diff -r c4f654de59cf gdb/dwarf2read.c
--- a/gdb/dwarf2read.c	Thu Nov 29 11:28:59 2007 -0800
+++ b/gdb/dwarf2read.c	Thu Nov 29 11:33:57 2007 -0800
@@ -1012,6 +1012,8 @@ static void store_in_ref_table (unsigned
 
 static unsigned int dwarf2_get_ref_die_offset (struct attribute *,
 					       struct dwarf2_cu *);
+
+static int dwarf2_attr_is_constant (struct attribute *);
 
 static int dwarf2_get_attr_constant_value (struct attribute *, int);
 
@@ -3380,8 +3382,11 @@ dwarf2_add_field (struct field_info *fip
       attr = dwarf2_attr (die, DW_AT_data_member_location, cu);
       if (attr)
 	{
-	  FIELD_BITPOS (*fp) =
-	    decode_locdesc (DW_BLOCK (attr), cu) * bits_per_byte;
+          if (dwarf2_attr_is_constant (attr))
+            FIELD_BITPOS (*fp) = dwarf2_get_attr_constant_value (attr, 0);
+          else
+            FIELD_BITPOS (*fp) =
+              decode_locdesc (DW_BLOCK (attr), cu) * bits_per_byte;
 	}
       else
 	FIELD_BITPOS (*fp) = 0;
@@ -9008,6 +9013,26 @@ dwarf2_get_ref_die_offset (struct attrib
   return result;
 }
 
+/* Return non-zero if ATTR's value falls in the 'constant' class, or
+   zero otherwise.  When this function returns true, you can apply
+   dwarf2_get_attr_constant_value to it.  */
+static int
+dwarf2_attr_is_constant (struct attribute *attr)
+{
+  switch (attr->form)
+    {
+    case DW_FORM_sdata:
+    case DW_FORM_udata:
+    case DW_FORM_data1:
+    case DW_FORM_data2:
+    case DW_FORM_data4:
+    case DW_FORM_data8:
+      return 1;
+    default:
+      return 0;
+    }
+}
+
 /* Return the constant value held by the given attribute.  Return -1
    if the value held by the attribute is not constant.  */