Re: [PATCH] Forward VALUE_LVAL when avoiding side effects for STRUCTOP_STRUCT

[Joel Brobecker <brobecker at adacore dot com>]

Hi Pierre-Marie,

> gdb/ChangeLog:
> 
> 	* eval.c (evaluate_subexp_standard) <STRUCTOP_STRUCT>: If
> 	EVAL_AVOID_SIDE_EFFECTS mode, forward the VALUE_LVAL attribute
> 	to the returned value.
> 
> gdb/testsuite/ChangeLog:
> 
> 	* gdb.base/nested-addr.c: New file.
> 	* gdb.base/nested-addr.exp: New testcase.

Comments below...

> diff --git a/gdb/eval.c b/gdb/eval.c
> index a668e76..84e2e34 100644
> --- a/gdb/eval.c
> +++ b/gdb/eval.c
> @@ -1862,7 +1862,7 @@ evaluate_subexp_standard (struct type *expect_type,
>        arg3 = value_struct_elt (&arg1, NULL, &exp->elts[pc + 2].string,
>  			       NULL, "structure");
>        if (noside == EVAL_AVOID_SIDE_EFFECTS)
> -	arg3 = value_zero (value_type (arg3), not_lval);
> +	arg3 = value_zero (value_type (arg3), VALUE_LVAL (arg3));
>        return arg3;

I'm not really sure this is a good idea to be doing that. We're building
somewhat of a fake "struct value", and the value's "discriminant" should,
in my mind at least, always reflect that through setting the lval to
"not_lval".

Have you tried modifying this function's handling of UNOP_ADDR
in the case of EVAL_AVOID_SIDE_EFFECTS instead? Add some code there
to return a not_lval value_zero with the correct type...

> +# Sanity checking:
> +gdb_test "print &foo_array\[1\].a" "= \\(int \\*\\) 0x.*"

Use "$hex.*" instead of "0x.*"...

> +# A bug in EVAL_AVOID_SIDE_EFFECTS mode used to yield the following error:
> +#    Attempt to take address of value not located in memory.
> +gdb_test "print 1 && &foo_array\[1\].a" "= 1"

-- 
Joel