From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm1-x333.google.com (mail-wm1-x333.google.com [IPv6:2a00:1450:4864:20::333]) by sourceware.org (Postfix) with ESMTPS id B1D2B389244D for ; Thu, 18 Feb 2021 14:01:31 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org B1D2B389244D Received: by mail-wm1-x333.google.com with SMTP id x16so3868811wmk.3 for ; Thu, 18 Feb 2021 06:01:31 -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:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=n1Boz45aoz9goTvo1QAfgh0ZmavNNRL27w2E8Km4ilM=; b=YAzGXaQSvMj5hS1V8IH76VsD0jofzDEOQH4bzK6zvUXdNYVBFiWiHttmXjFaNfgozn 7G7IAsvlQIq+qf5h6yi9lIl7NuulO3ZJPm64s4rWLoP39pEOqYkLHCKrUVHbJUvuBZSI 1EQcl19oq/EO0xw0hu0Ai+yod2lLcySrI8lkNxCPcYb+wLCT1nxYejSL/hg129iITBVO 2WCA45ri3O2xDHeB03Ctb1LQ57EdjxEayw348/uUjVg/5CAp319LWLCaGjdns7+Ic06R 82vRi8V1gtm1FhqnvMY7ePsemZs6h/1Ad8mVRLn8dcHpcjWhBCBCTJecCNcF/Mpufkhl PD4Q== X-Gm-Message-State: AOAM532xWbM5zzGcn2iEuaS+/oR8OmqOrJGr2XSF7hDFemrZibU9Bq02 dVL5q4CyAFHk6ZW//Sq0q1M= X-Google-Smtp-Source: ABdhPJxGZ6GBxKEAIZJgD2hgsO+WFxdleUd+rS77A52O/fNl36D26OgaxLUX2P3Vfnp4bhoTScRQ9Q== X-Received: by 2002:a7b:c747:: with SMTP id w7mr3738812wmk.140.1613656890324; Thu, 18 Feb 2021 06:01:30 -0800 (PST) Received: from [192.168.1.143] ([170.253.51.130]) by smtp.gmail.com with ESMTPSA id g1sm7942273wmh.9.2021.02.18.06.01.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 18 Feb 2021 06:01:29 -0800 (PST) Subject: Re: [RFC] execve.2: SYNOPSIS: Document both glibc wrapper and kernel sycalls To: "Michael Kerrisk (man-pages)" Cc: linux-man@vger.kernel.org, linux-kernel@vger.kernel.org, libc-alpha@sourceware.org, Florian Weimer References: <20210214133907.157320-1-alx.manpages@gmail.com> <1c7043ad-b834-5270-56fc-404d82d5a0a0@gmail.com> From: "Alejandro Colomar (man-pages)" Message-ID: <938df2c0-04b5-f6a4-79c3-b8fe09973828@gmail.com> Date: Thu, 18 Feb 2021 15:01:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <1c7043ad-b834-5270-56fc-404d82d5a0a0@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.3 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, KAM_SHORT, NICE_REPLY_A, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham 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, 18 Feb 2021 14:01:33 -0000 Hi Micahel, On 2/18/21 1:27 PM, Michael Kerrisk (man-pages) wrote: > Hi Alex, > > On 2/14/21 2:39 PM, Alejandro Colomar wrote: >> Until now, the manual pages have (usually) documented only either >> the glibc (or another library) wrapper for a syscall, or the raw >> syscall (this only when there's not a wrapper). >> >> Let's document both prototypes, which many times are slightly >> different. This will solve a problem where documenting glibc >> wrappers implied shadowing the documentation for the raw syscall. >> >> It will also be much clearer for the reader where the syscall >> comes from (kernel? glibc? other?), by adding an explicit comment >> at the beginning of the prototypes. This removes the need of >> scrolling down to NOTES to see that info. >> >> Signed-off-by: Alejandro Colomar >> --- >> >> Hi all, >> >> This is a prototype for doing some important changes to the SYNOPSIS >> of the man-pages. >> >> The commit message above explains the idea quite well. A few details >> that couldn't be shown on this commit are: >> >> For cases where the wrapper is provided by a library other than glibc, >> I'd simply change the comment. For example, for move_pages(2), >> it would say /* libnuma wrapper function: */. >> >> I think this would make the samll notes warning that there's no glibc >> wrapper function deprecated (but we could keep them for some time and >> decide that later). >> >> While changing this, I'd also make sure that the headers are correct, >> and clearly differentiate which headers are needed for the raw syscall >> and for the wrapper function. >> >> This change will probably take more than one release of the man-pages >> to complete. >> >> Any thoughts? > > My first impression is that I'm not keen on this. We'll add extra > text to all Section 2 pages, and in many (most?) cases the info > will be redundant (i.e., the wrapper and the syscall() notation > will express the same info). In other cases, I suspect the info > will be largely irrelevant to the user. To take an example: to > whom will the difference that you document below for execve() > matter, how will it matter, and does it matter enough that we > headline the info in the pages? I'd want cogent answers to > those questions before considering a wide-ranging change. It will matter to: 1) Users of old systems where the glibc wrapper is not yet present. 3) Users of some unicorn Linux distributions that use a C library different than glibc and may not have wrappers for some syscalls that glibc provides. 2) Library (libc) developers. Those won't have the glibc wrapper available for them, and will have to use syscall(2). The kernel syscall info would be highly valuable for them. However, the sum of them is probably not a big number of people. > > There are indeed cases where the wrapper API differs in > significant ways from the syscall API (and these differences > are usually captured in the " C library/kernel differences" > subsections, such as for pselect()/pselect6() in select(2)). > But I imagine that that is the case in only a smallish > minority of the pages. > > And indeed there are a very few syscalls that have wrappers > provided in another library. But it's a very small percentage > I think, and best documented case by case in specific pages. > The default presumption is that the wrapper is in the C library. Agree. > > There are other cases where I think it may be worthwhile > considering the syscall() notation: > > 1. Where the system call has no wrapper. In that case, we might > use the syscall() notation in the SYNOPISIS as both > (a) a clear indication that there is no wrapper and > (b) instructions to the reader about how to call the > system call using syscall(). Yes. > > 2. In cases where there is a "significant" difference between > the wrapper and the system call. In this case, we might > also place the syscall() notation in the SYNOPSIS, or > (perhaps more likely) in the NOTES Yes. I think it would be equally good to have the kernel syscall prototype in "C library/kernel ABI differences" in those cases where there is a glibc wrapper (even if it's quite different). It would be even better, as it would clearly mark the syscall(2) method as a second-class method, that should be avoided if possible. And also wouldn't add lines to the SYNOPSIS. However, we should probably have that subsection for all syscalls, including those where the prototype is very similar to the glibc one, to support those who need to use the kernel syscall, and provide them with the exact types that the kernel expects.(except for those unsupported by libraries, of course, which would have the syscall(SYS_xxx) prototype in the SYNOPSIS). I'll prepare a new RFC with this, with 2 pages: one with wrapper and one without wrapper. Thanks, Alex See also: > > Thanks, > > Michael > >> >> Thanks, >> >> Alex >> >> --- >> man2/execve.2 | 12 ++++++++++-- >> 1 file changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/man2/execve.2 b/man2/execve.2 >> index 639e3b4b9..87ff022ce 100644 >> --- a/man2/execve.2 >> +++ b/man2/execve.2 >> @@ -39,10 +39,18 @@ >> execve \- execute program >> .SH SYNOPSIS >> .nf >> +/* Glibc wrapper function: */ >> .B #include >> .PP >> -.BI "int execve(const char *" pathname ", char *const " argv [], >> -.BI " char *const " envp []); >> +.BI "int execve(const char *" pathname ", >> +.BI " char *const " argv "[], char *const " envp []); >> +.PP >> + /* Raw system call: */ >> +.B #include >> +.B #include >> +.PP >> +.BI "int syscall(SYS_execve, const char *" pathname , >> +.BI " const char *const " argv "[], const char *const " envp []); >> .fi >> .SH DESCRIPTION >> .BR execve () >> > > -- Alejandro Colomar Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/ http://www.alejandro-colomar.es/