https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101378
--- Comment #8 from Pedro Alves <pedro at palves dot net> --- Thank you, I missed the "same type" constraint. It's also mentioned at https://en.cppreference.com/w/cpp/language/attributes/no_unique_address . Indeed, if I use distinct empty types, GCC and Clang lay them at the same address: $ cat foo3.cc #include <stdio.h> #include <stddef.h> struct Empty1 {}; struct Empty2 {}; struct Empty3 {}; struct S { [[no_unique_address]] Empty1 empty1; [[no_unique_address]] Empty2 empty2; [[no_unique_address]] Empty3 empty3; } s; int main () { printf ("&s.empty1 = %p\n", &s.empty1); printf ("&s.empty2 = %p\n", &s.empty2); printf ("&s.empty3 = %p\n", &s.empty3); printf ("s = %p\n", &s); printf ("offset empty1 = %ld\n", offsetof (struct S, empty1)); printf ("offset empty2 = %ld\n", offsetof (struct S, empty2)); printf ("offset empty3 = %ld\n", offsetof (struct S, empty3)); return 0; } $ ./foo3 &s.empty1 = 0x55a5dc7aa031 &s.empty2 = 0x55a5dc7aa031 &s.empty3 = 0x55a5dc7aa031 s = 0x55a5dc7aa031 offset empty1 = 0 offset empty2 = 0 offset empty3 = 0 $ readelf -dw foo3| grep data_member_location <b6> DW_AT_data_member_location: -1 <c0> DW_AT_data_member_location: -1 <ca> DW_AT_data_member_location: -1 So (-1, -1, -1) in the DWARF and (0, 0, 0) at run time.
