Re: [PATCH 01/39] docs/spin: replace assert(0) with g_assert_not_reached()

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

On 9/11/24 09:13, Thomas Huth wrote:
> On 11/09/2024 14.51, Richard W.M. Jones wrote:
>> On Wed, Sep 11, 2024 at 02:46:18PM +0200, Maciej S. Szmigiero wrote:
>>> On 11.09.2024 14:37, Eric Blake wrote:
>>>> On Wed, Sep 11, 2024 at 07:33:59AM GMT, Eric Blake wrote:
>>>>> On Tue, Sep 10, 2024 at 03:15:28PM GMT, Pierrick Bouvier wrote:
>>>>>> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>>>>>> ---
>>>>>
>>>>> A general suggestion for the entire series: please use a commit
>>>>> message that explains why this is a good idea.  Even something as
>>>>> boiler-plate as "refer to commit XXX for rationale" that can be
>>>>> copy-pasted into all the other commits is better than nothing,
>>>>> although a self-contained message is best.  Maybe:
>>>>>
>>>>> This patch is part of a series that moves towards a consistent use of
>>>>> g_assert_not_reached() rather than an ad hoc mix of different
>>>>> assertion mechanisms.
>>>>
>>>> Or summarize your cover letter:
>>>>
>>>> Use of assert(false) can trip spurious control flow warnings from some
>>>> versions of gcc:
>>>> https://lore.kernel.org/qemu-devel/54bb02a6-1b12-460a-97f6-3f478ef766c6@linaro.org/
>>>> Solve that by unifying the code base on g_assert_not_reached()
>>>> instead.
>>>>
>>>
>>> If using g_assert_not_reached() instead of assert(false) silences
>>> the warning about missing return value in such impossible to reach
>>> locations should we also be deleting the now-unnecessary "return"
>>> statements after g_assert_not_reached()?
>>
>> Although it's unlikely to be used on any compiler that can also
>> compile qemu, there is a third implementation of g_assert_not_reached
>> that does nothing, see:
>>
>> https://gitlab.gnome.org/GNOME/glib/-/blob/927683ebd94eb66c0d7868b77863f57ce9c5bc76/glib/gtestutils.h#L269
> 
> That's only in the #ifdef G_DISABLE_ASSERT case ... and we forbid that in
> QEMU, see osdep.h:
> 
> #ifdef G_DISABLE_ASSERT
> #error building with G_DISABLE_ASSERT is not supported
> #endif
> 
> So in QEMU, g_assert_not_reached() should always abort.
> 
>    Thomas
> 

Yes indeed.

For further information:

g_assert_not_reached() expand to g_assertion_message_expr(), [1]
which is a function marked noreturn [2][3], so indeed, it always abort.

[1] 
https://gitlab.gnome.org/GNOME/glib/-/blob/927683ebd94eb66c0d7868b77863f57ce9c5bc76/glib/gtestutils.h#L274
[2] 
https://gitlab.gnome.org/GNOME/glib/-/blob/927683ebd94eb66c0d7868b77863f57ce9c5bc76/glib/gtestutils.h#L592
[3] https://docs.gtk.org/glib/macros.html#compiler