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GDB returns wrong type when traversing optimized-out Fields
- From: Roman Popov <ripopov at gmail dot com>
- To: gdb at sourceware dot org
- Date: Sun, 4 Feb 2018 20:02:11 -0800
- Subject: GDB returns wrong type when traversing optimized-out Fields
- Authentication-results: sourceware.org; auth=none
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