RE: [PATCH 02/10] type: add c99 variable length array support

["Agovic, Sanimir" <sanimir dot agovic at intel dot com>]

Thanks for your review.

> Sanimir> +  switch (ctx->location)
> Sanimir> +    {
> Sanimir> +    case DWARF_VALUE_REGISTER:
> Sanimir> +      *valp = dwarf_expr_read_reg (&baton, dwarf_expr_fetch_address (ctx, 0));
> Sanimir> +      break;
> Sanimir> +    case DWARF_VALUE_MEMORY:
> Sanimir> +      *valp = dwarf_expr_fetch_address (ctx, 0);
> Sanimir> +      break;
> Sanimir> +    }
> 
> It seems that something should be done for other DWARF_VALUE_* results
> here.
>
I will try, please have a closer look at this hunk in the upcoming v2.

> Sanimir> +struct type *
> Sanimir> +resolve_dynamic_type (struct type *type, CORE_ADDR address)
> Sanimir> +{
> [...]
> Sanimir> +  if (!TYPE_OBJFILE_OWNED (ty))
> Sanimir> +    return type;
> 
> This seems like a bit of a wart, though I am not sure whether the
> situation can actually arise.
> 
> 
> One thing I didn't see in here is error-checking of whether resolution
> makes sense.
> 
> E.g., suppose I print the value of a pointer-to-VLA.  Then I move to
> some other frame and "print *$".
> 
1| void foo (size_t n) {
2|   int vla[n];
3| }

(gdb) print &vla
$1 = (int (*)[42]) 0xffffffffffff
(gdb) up
(gdb) print *$
$2 = {0 <repeats 42 times>}
(gdb) down
(gdb) print *$
$3 = {0 <repeats 42 times>}

> In this situation the bounds have not been resolved -- but applying the
> DWARF expression in the currently-selected frame will silently do the
> wrong thing.
>
The bounds will be resolved in this case and therefore it is save to change
the frame+re-evaluate. If you have a different example in mind please tell
me and I see how to deal with it.

> I wonder if this series also needs to handle DW_AT_count.
> Maybe no compiler generates it.
> 
I will add a separate patch which implements DW_AT_count, I could not test
it as no compiler emits this attribute so far.


Below you will find the trivial reviews.

 -Sanimir

> -----Original Message-----
> From: Tom Tromey [mailto:tromey@redhat.com]
> Sent: Thursday, November 07, 2013 08:00 PM
> To: Agovic, Sanimir
> Cc: gdb-patches@sourceware.org
> Subject: Re: [PATCH 02/10] type: add c99 variable length array support
> 
> >>>>> "Sanimir" == Sanimir Agovic <sanimir.agovic@intel.com> writes:
> 
> Sanimir> The dwarf standard allow certain attributes to be expressed as
> Sanimir> dwarf expressions rather than constants. For instance
> Sanimir> upper-/lowerbound attributes.  In case of a c99 variable length
> Sanimir> array the upperbound is a dynamic attribute.
> 
> 
> Sanimir> +int
> Sanimir> +dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
> Sanimir> +			   CORE_ADDR addr, CORE_ADDR *valp)
> 
> Need an introductory comment.  It can just say "See dwarf2loc.h.", since
> you put the real comment there.
> 
Done.

> Sanimir> +static struct dwarf2_locexpr_baton* attr_to_locexprbaton
> Sanimir> +(const struct attribute *, struct dwarf2_cu *);
> Sanimir> +
> Sanimir> +static struct dwarf2_locexpr_baton* attr_to_locexprbaton_1
> Sanimir> +(const struct attribute *, struct dwarf2_cu *, const gdb_byte *additional_data,
> Sanimir> + int extra_size);
> Sanimir> +
> Sanimir> +static int attr_to_dwarf2_prop
> Sanimir> +(struct die_info *, const struct attribute *, struct dwarf2_cu *,
> Sanimir> + struct dwarf2_prop *);
> 
> In cases like this we usually indent the subsequent lines a bit, like:
> 
>     static int attr_to_dwarf2_prop
>         (struct die_info *, const struct attribute *, struct dwarf2_cu *,
>          struct dwarf2_prop *);
> 
> However in this case I think it may be preferable to rearrange the
> functions so that forward declarations are not needed.  What do you
> think?
> 
Done. Moved functions and dropped forward declaration.

> Sanimir> +static struct dwarf2_locexpr_baton*
> Sanimir> +attr_to_locexprbaton (const struct attribute *attribute, struct dwarf2_cu *cu)
> Sanimir> +{
> Sanimir> +  return attr_to_locexprbaton_1 (attribute, cu, NULL, 0);
> Sanimir> +}
> 
> If there is just a single caller (there is in this patch, but I haven't
> read all the patches yet), I would remove this function and just update
> the caller.
> 
Done. Folded function attr_to_locexprbaton/_1 into attr_to_locexprbaton.

> Sanimir> +static struct dwarf2_locexpr_baton*
> Sanimir> +attr_to_locexprbaton_1 (const struct attribute *attribute, struct dwarf2_cu *cu,
> Sanimir> +			const gdb_byte *additional_data, int extra_size)
> 
> Needs an introductory comment.
> 
Done.

> Sanimir> +    /* Copy the data pointer as the blocks lifetime is
> 
> Missing apostrophe: "block's".
> 
Done.

> Sanimir> +  gdb_assert(baton->data != NULL);
> 
> Space before open paren.
> 
Done.

> Sanimir> +/* Parse dwarf attribute if it's a block, reference or constant and put the
> Sanimir> +   resulting value of the attribute into struct dwarf2_prop. */
> Sanimir> +
> Sanimir> +static int
> Sanimir> +attr_to_dwarf2_prop (struct die_info *die, const struct attribute *attr,
> Sanimir> +		     struct dwarf2_cu *cu,
> Sanimir> +		     struct dwarf2_prop *prop)
> 
> I think it would be good if the introductory comment describe the return
> value.
> 
Done.

> Sanimir> +  else if (attr_form_is_ref (attr))
> Sanimir> +    {
> Sanimir> +      struct dwarf2_cu *target_cu = cu;
> Sanimir> +      struct die_info *target_die;
> Sanimir> +      struct attribute *target_attr;
> Sanimir> +      const gdb_byte append_ops[] = { DW_OP_deref };
> Sanimir> +
> Sanimir> +      target_die = follow_die_ref (die, attr, &target_cu);
> Sanimir> +      target_attr = dwarf2_attr (target_die, DW_AT_location, target_cu);
> Sanimir> +
> Sanimir> +      prop->data.locexpr =
> Sanimir> +	attr_to_locexprbaton_1 (target_attr, cu, append_ops,
> Sanimir> +				sizeof (append_ops) / sizeof (append_ops[0]));
> Sanimir> +      prop->kind = DWARF_LOCEXPR;
> Sanimir> +      gdb_assert (prop->data.locexpr != NULL);
> 
> I don't understand this hunk.  Could you say why it is needed?
> 
DW_AT_upper_bound may reference a die e.g. artificial variable, in this case we
need to read DW_AT_location of the target die. Some compilers emit this form to
implement vla. 

> Sanimir> +      dwarf2_invalid_attrib_class_complaint(dwarf_form_name (attr->form),
> Sanimir> +					    dwarf2_name (die, cu));
> 
> Missing space before a paren.
> 
Done.

> Sanimir> +static int
> Sanimir> +has_static_range (const struct range_bounds *bounds)
> Sanimir> +{
> Sanimir> +  return bounds->low.kind == DWARF_CONST
> Sanimir> +    && bounds->high.kind == DWARF_CONST;
> Sanimir> +}
> 
> THis needs parens around the argument to "return" and then an
> indentation fix on the second line.
> 
Done.

> Sanimir> +/* Calculates the size of a type given the upper and lower bound of a dynamic
> Sanimir> +   type.  */
> Sanimir> +
> Sanimir> +static ULONGEST
> Sanimir> +get_type_length (const struct type *type)
> Sanimir> +{
> Sanimir> +  const struct type *range_type, *target_type;
> Sanimir> +  ULONGEST len = TYPE_LENGTH (type);
> Sanimir> +  LONGEST low_bound, high_bound;
> Sanimir> +
> Sanimir> +  if (TYPE_CODE (type) != TYPE_CODE_ARRAY
> Sanimir> +      && TYPE_CODE (type) != TYPE_CODE_STRING)
> Sanimir> +    return len;
> Sanimir> +
> Sanimir> +  range_type = TYPE_INDEX_TYPE (type);
> Sanimir> +
> Sanimir> +  if (!has_static_range (TYPE_RANGE_DATA (range_type)))
> Sanimir> +    return len;
> 
> This seems like it doesn't follow what the introductory comment says it
> does.
> 
Fixed document.

> Sanimir> +
> Sanimir> +static void
> Sanimir> +resolve_dynamic_bounds (struct type *type, CORE_ADDR address)
> 
> Introductory comment.
> 
Done.

> Sanimir> +	  do {
> Sanimir> +	    struct type *range_type = TYPE_INDEX_TYPE (ary_dim);
> 
> It's hard to know but perhaps a check_typedef is required here.
> 
> Sanimir> +	    ary_dim = TYPE_TARGET_TYPE (ary_dim);
> 
> Here too.
> 
Done.




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