[commit/Ada] field of PAD structure is a non-scalar bitfield

[Joel Brobecker]

Hello,

We have noticed a problem in the debugger when trying to print a record
containing a packed array.  What happened is that the compiler wrapped
our variable into a PAD type.  These wrapper are often used to handle
alignment and packing.  exp_dbug.ads says, among other things:

      --  When the debugger sees an object of a type whose name has a
      --  suffix of ___PAD or ___JM, the type will be a record containing
      --  a single field, and the name of that field will be all upper case.
      --  In this case, it should look inside to get the value of the inner
      --  field, and neither the outer structure name, nor the field name
      --  should appear when the value is printed.

The problem appeared because the field inside the PAD record was
defined as a bit-field in the debugging info:

        .uleb128 0x24   # (DIE (0xf40) DW_TAG_member)
        .ascii "F\0"    # DW_AT_name
        .byte   0x9     # DW_AT_decl_file
        .byte   0x15    # DW_AT_decl_line
        .long   0xf50   # DW_AT_type
        .byte   0x4     # DW_AT_byte_size
        .byte   0x18    # DW_AT_bit_size
        .byte   0x8     # DW_AT_bit_offset
        .byte   0x2     # DW_AT_data_member_location
        .byte   0x23    # DW_OP_plus_uconst
        .uleb128 0x0

I just learned that Ada makes frequent uses of non-scalar bitfields.
And indeed, we have a function in ada-lang.c that we use to get
record fields which also happens to handle the case of bit-field
components as well (the function handles other cases such as
tagged types, variant records, etc).

So I fixed the problem by using that function to get the "F" field
inside our PAD type.

2008-05-02  Joel Brobecker  <brobecker@adacore.com>

        * ada-lang.c (unwrap_value): Handle the case where the "F" field
        inside a PAD type is a bitfield.

Tested on x86-linux, no regression.  Checked in.

-- 
Joel
-------------- next part --------------
Index: ada-lang.c
===================================================================
RCS file: /cvs/src/src/gdb/ada-lang.c,v
retrieving revision 1.139
diff -u -p -r1.139 ada-lang.c
--- ada-lang.c	30 Apr 2008 21:13:49 -0000	1.139
+++ ada-lang.c	2 May 2008 23:40:33 -0000
@@ -7973,8 +7973,7 @@ unwrap_value (struct value *val)
   struct type *type = ada_check_typedef (value_type (val));
   if (ada_is_aligner_type (type))
     {
-      struct value *v = value_struct_elt (&val, NULL, "F",
-                                          NULL, "internal structure");
+      struct value *v = ada_value_struct_elt (val, "F", 0);
       struct type *val_type = ada_check_typedef (value_type (v));
       if (ada_type_name (val_type) == NULL)
         TYPE_NAME (val_type) = ada_type_name (type);