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

[Christian Schoenebeck]

On Montag, 8. März 2021 15:30:23 CET Philippe Mathieu-Daudé wrote:
> On 3/8/21 3:17 PM, Akihiko Odaki wrote:
> > 2021年3月8日(月) 23:03 Christian Schoenebeck <qemu_oss@crudebyte.com>:
> >> BTW, there is __nonnull supported by clang, e.g.:
> >> 
> >> static void foo(void *__nonnull p) {
> >> 
> >>         ...
> >> 
> >> }
> >> 
> >> Maybe as an optionally defined macro (if supported by compiler) this
> >> could be a useful tool for such intended nonnull designs, as it
> >> immediately emits compiler errors.
> >> 
> >> Best regards,
> >> Christian Schoenebeck
> > 
> > GCC has nonnull attribute and clang accepts it too. However, it
> > specifies argument indices, which is harder to understand and to
> > maintain.
> > __attribute__((nonnull(2)))
> > void f(void *k, void *l);
> 
> Richard once suggested to add QEMU_NONNULL(), I have been using
> it on a series trying to enforce non-null uses of QOM
> 'struct Object *owner' but it didn't work out because migrations
> of MemoryRegion, some have NULL owner in MachineState.
> 
> I also discarded it because Daniel said it could have side-effects
> https://www.mail-archive.com/qemu-devel@nongnu.org/msg720739.html

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