Re: [PATCHv2 2/2] gdb/fortran: Access elements of a structure with dynamic type

[Tom Tromey <tom@tromey.com>]

>>>>> "Andrew" == Andrew Burgess <andrew.burgess@embecosm.com> writes:

Andrew>      case STRUCTOP_STRUCT:
Andrew>        tem = longest_to_int (exp->elts[pc + 1].longconst);
Andrew>        (*pos) += 3 + BYTES_TO_EXP_ELEM (tem + 1);
Andrew> +      oldpos = *pos;
Andrew>        arg1 = evaluate_subexp (NULL_TYPE, exp, pos, noside);
Andrew>        if (noside == EVAL_SKIP)
Andrew>  	return eval_skip_value (exp);
Andrew> +      if (noside == EVAL_AVOID_SIDE_EFFECTS)
Andrew> +	{
Andrew> +	  /* If the element of the structure has a dynamic type then we
Andrew> +	     need to get the real value representing the containing
Andrew> +	     structure so that we can correctly evaluate the type of the
Andrew> +	     element.  If we're not already avoiding side effects then we
Andrew> +	     already have the real value of the containing structure, so
Andrew> +	     this is not needed.  */
Andrew> +	  type = lookup_struct_elt_type (value_type (arg1),
Andrew> +					 &exp->elts[pc + 2].string, 1);
Andrew> +	  if (type != nullptr && is_dynamic_type (type))
Andrew> +	    {
Andrew> +	      *pos = oldpos;
Andrew> +	      arg1 = evaluate_subexp (NULL_TYPE, exp, pos, EVAL_NORMAL);

Re-evaluating a subexpression like this can lead to problems; see for
example commit 6830f270e ("Avoid exponential behavior in rust_evaluate_subexp").

I don't know if there's another way to do this, though.

Tom