Hi Martin, Thanks! It's good to learn some GCC internal details :) Cheers, Alex On 12/18/20 5:51 PM, Martin Sebor wrote: > On 12/18/20 3:42 AM, Alejandro Colomar (man-pages) wrote: >> 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 *'. > > __builtin___clear_cache was added to GCC in r126535 (the __builtin_ > prefix is added by the macro): > > +DEF_EXT_LIB_BUILTIN (BUILT_IN_CLEAR_CACHE, "__clear_cache", > BT_FN_VOID_PTR_PTR, ATTR_NOTHROW_LIST) > > The BT_FN_VOID_PTR_PTR macro describes its signature as returning > void and taking two void pointer arguments. AFAIK, this has never > changed. Contrary to that, the manual entry for the built-in added > in the same revision documented it as taking two char*. That was > corrected to void* in r269082 to match. > > There's a GCC internal declaration of __clear_cache (apparently > provided in libgcc for VxWorks). It was added in r264479 and > it also used char*. This was also changed to void* in r269082 > to match the built-in. Looks like this __clear_cache has just > been removed from libgcc in GCC 11: > https://gcc.gnu.org/pipermail/gcc-cvs/2020-December/338478.html > >>> >>> Where is the actual prototype exposed to the user declared? > > Built-in functions are declared implicitly by GCC. They have no > explicit declarations like user-defined functions. The implicit > internal "declarations" are specified in the GCC internal file > gcc/builtins.def, where they are hidden behind layers of macros. > For example, on the GCC 10 branch, the declaration for > __builtin___clear_cache is here: > > https://gcc.gnu.org/git/?p=gcc.git;a=blob;f=gcc/builtins.def;h=fa8b0641ab13b36f983c591a7020f6b432e5fb3d;hb=refs/heads/releases/gcc-10#l837 > > > Martin > >>> >>> 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/
