From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-x341.google.com (mail-wm1-x341.google.com [IPv6:2a00:1450:4864:20::341]) by sourceware.org (Postfix) with ESMTPS id 37386398BC04 for ; Thu, 1 Oct 2020 16:55:08 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 37386398BC04 Received: by mail-wm1-x341.google.com with SMTP id 13so150820wmf.0 for ; Thu, 01 Oct 2020 09:55:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=6thW6uIzKo0AKUx3z1dt90fnAdUCuGiPlcRQ/kj9HnY=; b=D8Kz6gYrWRZbVijc3OzoBT2JKbnNBPGJdzYFi5/ekvKuAAVM9ps0zY/ZaWLAlaNOyV 9QzjQvQD0UzSVYaZpLQFo7z7u7P8N/oUuVsfau+IRycGBoi6fJ6mhk6J6SW7dj6b+YW/ OWaoxgdM/vEgIMYaJNmIZ1yvSXDfagUOP2CQJORiB6VFObdW/AT4p1rx4gFWzV6Dom3O icIrPkA6LakzKRPs2iG1abeKjYyTUjumUotO3OeK6sX5FMRFNgb13AXtVhkbrnvlIqb3 A90vLygbGtwjQdjInfiF1cdAwW7+07VWebYgsG7LHW0zf+y2Q2jUF0mXW/k3q+mmQ+re mFaQ== X-Gm-Message-State: AOAM530cKENPtcwQePKMApHJ5in0ZqCKr9fWJJFhQ0URNRzkksZrv8cC E+1mL+J4vJAGQQI0NKYZ57ttyx5sbZDD0w== X-Google-Smtp-Source: ABdhPJynBwL8B/dPnbv/POOgme/EYgQ8xb2q9YNIKii1u4FdsmU899H5MSVGe6Nc3+BzGOiOrDfrNg== X-Received: by 2002:a05:600c:215:: with SMTP id 21mr921762wmi.105.1601571306836; Thu, 01 Oct 2020 09:55:06 -0700 (PDT) Received: from [192.168.1.143] ([170.253.60.68]) by smtp.gmail.com with ESMTPSA id n2sm858530wma.29.2020.10.01.09.55.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 01 Oct 2020 09:55:06 -0700 (PDT) Subject: Re: [PATCH v2 1/2] system_data_types.7: Add 'void *' To: "Michael Kerrisk (man-pages)" Cc: linux-man@vger.kernel.org, gcc@gcc.gnu.org, libc-alpha@sourceware.org References: <41affebd-3354-9420-0048-bffd14535e95@gmail.com> <20201001154946.104626-2-colomar.6.4.3@gmail.com> From: Alejandro Colomar Message-ID: <41ab7ed9-3ce0-f8ad-38f4-c4bbeca138f8@gmail.com> Date: Thu, 1 Oct 2020 18:55:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-4.9 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_ENVFROM_END_DIGIT, FREEMAIL_FROM, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=unavailable autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 01 Oct 2020 16:55:09 -0000 On 2020-10-01 18:38, Michael Kerrisk (man-pages) wrote: > Hi Alex, > >> +According to the C language standard, >> +a pointer to any object type may be converted to a pointer to >> +.I void >> +and back. >> +POSIX further requires that any pointer, >> +including pointers to functions, >> +may be converted to a pointer to >> +.I void >> +and back. > I know you are correct about POSIX, but which part of the > standard did you find this information in? The only > reference that I find in POSIX is the dlsym() spec. Is it > covered also somewhere else in the standrd? > > Thanks, > > Michael > Hi Michael, I've bean searching, and dlsym is the only one: ________ user@debian:~/Desktop/src/Standards/susv4-2018$ grep -rn "pointer to a function" functions/regfree.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

functions/dlsym.html:138:

Note that conversion from a void * pointer to a function pointer as in:

functions/regcomp.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

functions/regexec.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

functions/V2_chap02.html:3039:

There are three types of action that can be associated with a signal: SIG_DFL, SIG_IGN, or a pointer to a function. Initially, functions/regerror.html:530:"undefined" means that the action by the application is an error, of similar severity to passing a bad pointer to a function.

user@debian:~/Desktop/src/Standards/susv4-2018$ grep -rn "function pointer" basedefs/glob.h.html:165:"../functions/glob.html">glob() prototype definition by removing the restrict qualifier from the function pointer xrat/V4_xsh_chap02.html:114:when the application requires it; for example, if its address is to be stored in a function pointer variable.

functions/dlsym.html:138:

Note that conversion from a void * pointer to a function pointer as in:

user@debian:~/Desktop/src/Standards/susv4-2018$ grep -rn "pointer to function" functions/dlsym.html:73:converted from type pointer to function to type pointer to void; otherwise, dlsym() shall return the address of the user@debian:~/Desktop/src/Standards/susv4-2018$ From those, the only one that documents this is functions/dlsym. The rest is noise. The most explicit paragraph in dlsym is the following: [[ Note that conversion from a void * pointer to a function pointer as in: fptr = (int (*)(int))dlsym(handle, "my_function"); is not defined by the ISO C standard. This standard requires this conversion to work correctly on conforming implementations. ]]