[cfe-users] Ping: cacheflush.2

[Alejandro Colomar (man-pages) via cfe-users]

Hi Martin,

I sent you an email, but I received a "delivery failure".
If you're reading this from a list, could you answer, please?

Thanks,

Alex

On 12/14/20 11:34 PM, Alejandro Colomar (man-pages) wrote:
> Hello Martin,
> 
> Thanks for the correction!
> Then the prototypes that changes from 'char *' to 'void *' in r269082
> were not exposed to the user, right?
> I guess then those are just internal implementation where GCC did use
> 'char *'.
> 
> Where is the actual prototype exposed to the user declared?
> 
> Thanks,
> 
> Alex
> 
> P.S.: Michael, wait for a patch revision (v6).
> 
> On 12/14/20 10:13 PM, Martin Sebor wrote:
>> On 12/11/20 11:14 AM, Alejandro Colomar (man-pages) via Gcc wrote:
>>> It looks like GCC recently moved from 'char *' to 'void *'.
>>> This SO question[1] (4 years ago) quotes the GCC docs
>>> and they had 'char *'.
>>
>> __builtin___clear_cache in GCC has always been declared to take
>> void*.  The signature in the manual was recently corrected to match
>> the implementation, i.e., from char* to void*, in r269082.
>>
>> Martin
>>
>>> Maybe Clang hasn't noticed the change.
>>> I'll report a bug.
>>>
>>> [1]: https://stackoverflow.com/q/35741814/6872717
>>>
>>> On 12/9/20 8:15 PM, Alejandro Colomar (man-pages) wrote:
>>>> Hi Heinrich,
>>>>
>>>> It looks like a bug (or at least an undocumented divergence from GCC) in
>>>> Clang/LLVM.  Or I couldn't find the documentation for it.
>>>>
>>>> Clang uses 'char *':
>>>> https://github.com/llvm/llvm-project/blob/7faf62a80bfc3a9dfe34133681fcc31f8e8d658b/clang/include/clang/Basic/Builtins.def#L583
>>>>
>>>>
>>>> GCC uses 'void *':
>>>> https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
>>>>
>>>> I CCd Clang and GCC lists; maybe they know about that divergence.
>>>>
>>>> Cheers,
>>>>
>>>> Alex
>>>>
>>>> On 12/9/20 7:48 PM, Heinrich Schuchardt wrote:
>>>>> On 12/9/20 7:34 PM, Alejandro Colomar (man-pages) wrote:
>>>>>> Hi Heinrich & Michael,
>>>>>>
>>>>>> What about the following?:
>>>>>>
>>>>>> [
>>>>>> NOTES
>>>>>>          GCC provides a similar function, which may be useful on 
>>>>>> archi‐
>>>>>>          tectures that lack this system call:
>>>>>>
>>>>>>              void __builtin___clear_cache(void *begin, void *end);
>>>>>> ]
>>>>>
>>>>> I just checked building with Clang/LLVM. There the arguments are of
>>>>> type
>>>>> (char *). See the following error output:
>>>>>
>>>>> +arch/sandbox/cpu/cache.c:19:26: error: passing 'uint8_t *' (aka
>>>>> 'unsigned char *') to parameter of type 'char *' converts between
>>>>> pointers to integer types with different sign [-Werror,-Wpointer-sign]
>>>>> +        __builtin___clear_cache(state->ram_buf,
>>>>> +                                ^~~~~~~~~~~~~~
>>>>> +arch/sandbox/cpu/cache.c:20:12: error: passing 'uint8_t *' (aka
>>>>> 'unsigned char *') to parameter of type 'char *' converts between
>>>>> pointers to integer types with different sign [-Werror,-Wpointer-sign]
>>>>> +                                state->ram_buf + state->ram_size);
>>>>> +                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>>>>
>>>>> Best regards
>>>>>
>>>>> Heinrich
>>>>>
>>>>>>
>>>>>> Cheers,
>>>>>>
>>>>>> Alex
>>>>>>
>>>>>> On 12/9/20 7:04 PM, Heinrich Schuchardt wrote:
>>>>>>> Hello Michael,
>>>>>>>
>>>>>>> function cacheflush() does not exist on many architectures.
>>>>>>>
>>>>>>> It would have saved me a lot of time if the man-page had referenced
>>>>>>> GCC's
>>>>>>>
>>>>>>> void __builtin___clear_cache(void *begin, void *end)
>>>>>>>
>>>>>>> Maybe you can add it to NOTES.
>>>>>>>
>>>>>>> Best regards
>>>>>>>
>>>>>>> heirnich
>>>>>>
>>>>>
>>>>
>>>
>>
> 

-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/