[Bug sanitizer/66514] UBSAN: Add -fsanitize=lifetime

["marxin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66514

--- Comment #3 from Martin LiÅka <marxin at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> There is some minimal support in -fsanitize=vptr, but that catches only
> destructed objects with virtual methods (by disabling the clobbers and
> clearing the vptr).

I see.

> Other than that, this is something that is more in line with the address
> sanitizer (which also has very limited support for file scope objects, but
> only makes the objects unavailable during construction of each TU, so
> catches constructor ordering issues within a single TU).  Other than that,
> the concept of making a chunk of memory available at certain point and
> unavailable at another point is something -fsanitize=address is able to do. 
> The question is what can be done with operator new, e.g. if you have a char
> buffer in some class and construct something else at that spot, then
> destructing it; reading those bytes afterwards is supposedly UB, but storing
> there something say with memcpy shouldn't be invalid.

Ok, after reading your caution and test-cases mentioned in the ASAN tracker, I
think emitting a poison memory call in a dtor for instances that does not use
placement new can be beneficial. However, I can't evaluate if getting such kind
of information in doable in GCC?