[cfe-users] cacheflush.2

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

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