Re: Missed warning (-Wuse-after-free)

[Siddhesh Poyarekar <siddhesh@gotplt.org>]

On 2023-02-16 10:15, David Malcolm via Gcc wrote:
> I'm not convinced that it's useful to the end-user to warn about the
> "use of q itself" case.

FWIW, -Wuse-after-free=3 already should do this:

At level 3, the warning also diagnoses uses of indeterminate pointers in 
equality expressions.  All uses of indeterminate pointers are undefined 
but equality tests sometimes appear after
calls to "realloc" as an attempt to determine whether the call resulted 
in relocating the object to a different address.  They are diagnosed at 
a separate level to aid legacy code gradually
transition to safe alternatives.  For example, the equality test in the 
function below is diagnosed at this level:

Jakub and I had discussed this in the context of _FORTIFY_SOURCE=3 
(which is anal about this and can break things) and we got pr#105217, 
but that is also a best-effort thing, not really a guarantee.

IMO the analyzer should go that extra mile and warn for the use of q 
itself and maybe deprecate -Wuse-after-free=3 in its favour.

Sid