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dwarf2loc.c: Perform a pointer to address conversion for DWARF_VALUE_MEMORY. 

This patch fixes the following failures for rl78-elf:

FAIL: gdb.base/vla-datatypes.exp: print int_vla
FAIL: gdb.base/vla-datatypes.exp: print unsigned_int_vla
FAIL: gdb.base/vla-datatypes.exp: print double_vla
FAIL: gdb.base/vla-datatypes.exp: print float_vla
FAIL: gdb.base/vla-datatypes.exp: print long_vla
FAIL: gdb.base/vla-datatypes.exp: print unsigned_long_vla
FAIL: gdb.base/vla-datatypes.exp: print char_vla
FAIL: gdb.base/vla-datatypes.exp: print short_vla
FAIL: gdb.base/vla-datatypes.exp: print unsigned_short_vla
FAIL: gdb.base/vla-datatypes.exp: print unsigned_char_vla
FAIL: gdb.base/vla-datatypes.exp: print foo_vla
FAIL: gdb.base/vla-datatypes.exp: print bar_vla
FAIL: gdb.base/vla-datatypes.exp: print vla_struct_object
FAIL: gdb.base/vla-datatypes.exp: print vla_union_object
FAIL: gdb.base/vla-ptr.exp: print td_vla
FAIL: gdb.mi/mi-vla-c99.exp: evaluate complete vla

The first failure in this bunch occurs due to printing an incorrect
result for a variable length array:

    print int_vla
    $1 = {-1, -1, -1, -1, -1}

The result should actually be this:

    $1 = {0, 2, 4, 6, 8}

When I started examining this bug, I found that printing an
individual array element worked correctly.  E.g. "print int_vla[2]"
resulted in 4 being printed.  I have not looked closely to see why
this is the case.

I found that evaluation of the location expression for int_vla was
causing problems.  This is the relevant DWARF entry for int_vla:

<2><15a>: Abbrev Number: 10 (DW_TAG_variable)
    <15b>   DW_AT_name        : (indirect string, offset: 0xbf): int_vla
    <15f>   DW_AT_decl_file   : 1
    <160>   DW_AT_decl_line   : 35
    <161>   DW_AT_type        : <0x393>
    <165>   DW_AT_location    : 4 byte block: 86 7a 94 2  (DW_OP_breg22 (r22): -6; DW_OP_deref_size: 2)

I found that DW_OP_breg22 was providing a correct result.
DW_OP_deref_size was fetching the correct value from memory.  However,
the value being fetched should be considered a pointer.
DW_OP_deref_size zero extends the fetched value prior to pushing
it onto the evaluation stack.  (The DWARF-4 document specifies this
action; so GDB is faithfully implementing the DWARF-4 specification.)

However, zero extending the pointer is not sufficient for converting
that value to an address for rl78 and (perhaps) other architectures
which define a `pointer_to_address' method.  (I suspect that m32c
would have the same problem.)

Ideally, we would perform the pointer to address conversion in
DW_OP_deref_size.  We don't, however, know the type of the object
that the address refers to in DW_OP_deref_size.  I can't think
of a way to infer the type at that point in the code.

Before proceeding, I should note that there are two other DWARF
operations that could be used in place of DW_OP_deref_size.  One of
these is DW_OP_GNU_deref_type.  Current GDB implements this operation,
but as is obvious from the name, it is non-standard DWARF.  The other
operation is DW_OP_xderef_size.  Even though it's part of DWARF-2
through DWARF-4 specifications, it's not presently implemented in GDB.
Present day GCC does not output dwarf expressions containing this
operation either.  [Of the two, I like DW_OP_GNU_deref_type better.
Using it avoids the need to specify an "address space identifier".
(GCC, GDB, and other non-free tools all need to agree on the meanings
of these identifiers.)]

Back to the bug analysis...

The closest consumer of the DW_OP_deref_size result is the
DWARF_VALUE_MEMORY case in dwarf2_evaluate_loc_desc_full.  At that
location, we do know the object type to which the address is intended
to refer.  I added code to perform a pointer to address conversion at
this location.  (See the patch.)

I do have some misgivings regarding this patch.  As noted earlier, it
would really be better to perform the pointer to address conversion in
DW_OP_deref_size.  I can't, however, think of a way to make this work.
Changing GCC to output one of the other aforementioned operations might
be preferable but, as noted earlier, these solutions have problems as
well.  Long term, I think it'd be good to have something like
DW_OP_GNU_deref_type become part of the standard.  If that can't or
won't happen, we'll need to implement DW_OP_xderef_size.

But until that happens, this patch will work for expressions in which
DW_OP_deref_size occurs last.  It should even work for dereferences
followed by adding an offset.  I don't think it'll work for more than
one dereference in the same expression.

gdb/ChangeLog:

	* dwarf2loc.c (dwarf2_evaluate_loc_desc_full): Perform a pointer
	to address conversion for DWARF_VALUE_MEMORY.
This commit is contained in:
Kevin Buettner 2015-11-24 21:53:13 -07:00
parent 5fc2beac27
commit f56331b468
2 changed files with 26 additions and 0 deletions
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5
gdb/ChangeLog
View File

@ -1,3 +1,8 @@
2015-12-09 Kevin Buettner <kevinb@redhat.com>
* dwarf2loc.c (dwarf2_evaluate_loc_desc_full): Perform a pointer
to address conversion for DWARF_VALUE_MEMORY.
2015-12-09 Luis Machado <lgustavo@codesourcery.com>
* gdb/mi/mi-cmd-var.c (mi_parse_format): Handle new "zero-hexadecimal"

21
gdb/dwarf2loc.c
View File

@ -2343,9 +2343,30 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
case DWARF_VALUE_MEMORY:
{
struct type *ptr_type;
CORE_ADDR address = dwarf_expr_fetch_address (ctx, 0);
int in_stack_memory = dwarf_expr_fetch_in_stack_memory (ctx, 0);
/* DW_OP_deref_size (and possibly other operations too) may
create a pointer instead of an address. Ideally, the
pointer to address conversion would be performed as part
of those operations, but the type of the object to
which the address refers is not known at the time of
the operation. Therefore, we do the conversion here
since the type is readily available. */
switch (TYPE_CODE (type))
{
case TYPE_CODE_FUNC:
case TYPE_CODE_METHOD:
ptr_type = builtin_type (ctx->gdbarch)->builtin_func_ptr;
break;
default:
ptr_type = builtin_type (ctx->gdbarch)->builtin_data_ptr;
break;
}
address = value_as_address (value_from_pointer (ptr_type, address));
do_cleanups (value_chain);
retval = value_at_lazy (type, address + byte_offset);
if (in_stack_memory)