From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr1-x433.google.com (mail-wr1-x433.google.com [IPv6:2a00:1450:4864:20::433]) by sourceware.org (Postfix) with ESMTPS id AB5923857C5F for ; Sat, 19 Dec 2020 14:04:24 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org AB5923857C5F Received: by mail-wr1-x433.google.com with SMTP id r7so6048935wrc.5 for ; Sat, 19 Dec 2020 06:04:24 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:cc:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=QKhQfxKR1/k5Vkjj/hR3jkZZkxoJtEMOFVhLtaTOQDE=; b=Em7BVG6u3lhXN6Kra+jHzY3TjpyuLhWGGl94Sik1JHr4rR2bVP4MDUNBWcLxi3sA1T DmfeI8jt5yB26YlC/8njGPVpyuZz5P9Y6kruy/nyLKje1u2fLRHqIRryiUHpZqG3oEAu FRvCDYnyEXyZtnELdQNMKeIFW451uCR5SSjmP3/q1XJkSzHOZsM2m9KVaA+vCQtWpmf9 jpOEGgRz7QhV0/rpo8Dx+U2ScNFrDjwWuWbJ6vQ7oH4A2tjroIzxKgFw1S4XZXMmGGS3 nh0kwViPt9ZkKoZd5xO69jv8CGQKRIGGbM4KhssOYdqXDnWbwW/YNkOZh5gTBGFLb4X1 MU9w== X-Gm-Message-State: AOAM530VdPMZSRQaFrGXTnqPP5ENmPLdpQVERAwX2LsRaCKzAj4pZMFG PGXQ8REkD5QXSRfmRKvxdHU= X-Google-Smtp-Source: ABdhPJzxaRU1KRc9MnRYyQBfH8PILfa321HyopHnjsifKYOBclWCQZ9o3Uhq16cYJ9M141HkMDRwUQ== X-Received: by 2002:adf:e512:: with SMTP id j18mr9634708wrm.52.1608386663722; Sat, 19 Dec 2020 06:04:23 -0800 (PST) Received: from [192.168.1.143] ([170.253.51.130]) by smtp.gmail.com with ESMTPSA id g192sm15542994wme.48.2020.12.19.06.04.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 19 Dec 2020 06:04:23 -0800 (PST) Subject: Re: Ping: cacheflush.2 To: Martin Sebor References: <794cf0d1-d528-4b5a-3ce0-b1b5f588dc6d@gmx.de> <5257a883-29f0-6eaa-5708-d1f47356a57a@gmx.de> <90152ea6-f2eb-b08f-7269-f8266ffb15d1@gmail.com> <52a37c46-3488-957c-fc50-6caca177cb3c@gmail.com> <64bd5678-4c25-668d-39b2-31c825253d1b@gmail.com> <6ed5bc42-1d18-e963-fecc-cc9b1bfb2a2c@gmail.com> Cc: Heinrich Schuchardt , gcc@gcc.gnu.org, cfe-users@lists.llvm.org, "Michael Kerrisk (man-pages)" , linux-man@vger.kernel.org, Dave Martin From: "Alejandro Colomar (man-pages)" Message-ID: <68174956-2f57-0c7d-c54c-768e31f8fb62@gmail.com> Date: Sat, 19 Dec 2020 15:04:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00, BODY_8BITS, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, KAM_NUMSUBJECT, KAM_SHORT, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 19 Dec 2020 14:04:26 -0000 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/