[cfe-users] cacheflush.2

[Martin Sebor via cfe-users]

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
>>>>
>>>
>>
>