Re: [PATCH] ui/gtk: fix NULL pointer dereference

[Akihiko Odaki]

2021年3月8日(月) 23:58 Christian Schoenebeck <qemu_oss@crudebyte.com>:
>
> Yes, but the optimizer part could be disabled with
> -fno-delete-null-pointer-checks which would render it a pure diagnostic
> feature:
>
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-nonnull-function-attribute
>
> Is there an example where the compiler failed to detect a NULL user case?
>
> Best regards,
> Christian Schoenebeck
>
>

-fno-delete-null-pointer-checks also prevents the compiler to infer
that a pointer is never NULL with the fact it is dereferenced
somewhere else. It also disables
-fisolate-erroneous-paths-dereference, which turns code paths with
NULL pointer dereferences into traps. I suspect these side effects are
too important to ignore.

Perhaps we may define QEMU_NONNULL as once it was, and document that
it affects runtime behaviors and should not be blindly added to
functions that already exist. We may also be able to enable
-fisolate-erroneous-paths-attribute, which turns code paths with NULL
pointer passing to such functions into traps, if we explicitly state
that it has runtime effects.

Regards,
Akihiko Odaki