Re: GDB returns wrong type when traversing optimized-out Fields

[Roman Popov <ripopov@gmail.com>]

I apologize for code typo in previous email. Here is correct code sample:

template <unsigned v1, unsigned v2>
struct TRAITS {
    static const unsigned val1 = v1;
    static const unsigned val2 = v2;
};
template < class TRAITS >
struct foo {
    static const unsigned x1 = TRAITS::val1;
    static const unsigned x2 = TRAITS::val2;
};

int main () {
    foo<TRAITS<1,2>> f1;
    // SET BREAKPOINT HERE
    return 0;
}

-Roman


2018-02-04 20:02 GMT-08:00 Roman Popov <ripopov@gmail.com>:

> Hi all,
> I've encountered strange GDB behavior when requesting a value of
> optimized-away field.
> Instead of returning None or raising exception, GDB returns an
> optimizied-out value of wrong type.
>
> Here is a small reproducer *optimize_out.cpp*:
>
> template <unsigned v1, unsigned v2>
> struct TRAITS {
>     static const unsigned val1 = v1;
>     static const unsigned val2 = v2;
> };
> template < class TRAITS >
> struct foo {
>     static const unsigned x1 = TRAITS::v1;
>     static const unsigned x2 = TRAITS::v2;
> };
>
> int main () {
>     foo<TRAITS<1,2>> f1;
>     // SET BREAKPOINT HERE
>     return 0;
> }
>
> # Using g++ 7.3
> $ g++ -g optimize_out.cpp
>
> # Using gdb 8.1
> $ gdb a.out
>
> (gdb) break optimize_out.cpp:14
> (gdb) r
> (gdb) p f1
> $1 = {static x1 = <optimized out>, static x2 = <optimized out>}
>
> Ok, looks good.  Now traverse fields:
>
> (gdb) python
> >f1 = gdb.parse_and_eval("f1")
> >for field in f1.type.fields():
> >    print ("field name: ", field.name, "field type: ", field.type)
> >    field_val = f1[field]
> >    print ("optout?: ",field_val.is_optimized_out, "type:
> ",field_val.type)
> >end
> field name:  x1 field type:  const unsigned int
> optout?:  True type:  foo<TRAITS<1, 2> >
> field name:  x2 field type:  const unsigned int
> optout?:  True type:  foo<TRAITS<1, 2> >
>
>
>
> So type we get is foo<TRAITS<1, 2> >, not unsigned int.
>
> Looks like GDB-MI has same behavior. At least this code sample totatlly
> confuses GDB GUI I use.
>
> Thanks,
> Roman
>