[PATCH v5 5/9] powerpc/mm/book3s64: Update tlb flush routines to take a page walk cache flush argument

[Guenter Roeck]

On 5/19/21 5:03 AM, Segher Boessenkool wrote:
> On Tue, May 18, 2021 at 07:45:14PM -0500, Segher Boessenkool wrote:
>> On Wed, May 19, 2021 at 10:26:22AM +1000, Michael Ellerman wrote:
>>> Guenter Roeck <linux at roeck-us.net> writes:
>>>> Ah, sorry. I wasn't aware that the following is valid C code
>>>>
>>>> void f1()
>>>> {
>>>>       return f2();
>>>>       ^^^^^^
>>>> }
>>>>
>>>> as long as f2() is void as well. Confusing, but we live and learn.
>>>
>>> It might be valid, but it's still bad IMHO.
>>>
>>> It's confusing to readers, and serves no useful purpose.
>>
>> And it actually explicitly is undefined behaviour in C90 already
>> (3.6.6.4 in C90, 6.8.6.4 in C99 and later).
> 
> ... but there is a GCC extension that allows this by default:
> <https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wreturn-type>
>    For C only, warn about a 'return' statement with an expression in a
>    function whose return type is 'void', unless the expression type is
>    also 'void'.  As a GNU extension, the latter case is accepted
>    without a warning unless '-Wpedantic' is used.
> 

In C99:

"6.8.6.4 The return statement
Constraints

A return statement with an expression shall not appear in a function whose return type
is void. A return statement without an expression shall only appear in a function
whose return type is void."

Sounds like invalid to me, not just undefined behavior.

Guenter