[cfe-users] cacheflush.2

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

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; http://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es