From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-x72b.google.com (mail-qk1-x72b.google.com [IPv6:2607:f8b0:4864:20::72b]) by sourceware.org (Postfix) with ESMTPS id 73C6B385480B for ; Wed, 7 Apr 2021 18:53:00 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 73C6B385480B Received: by mail-qk1-x72b.google.com with SMTP id x11so19790804qkp.11 for ; Wed, 07 Apr 2021 11:53:00 -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=l+Xgp5JloDWLdLwKGbX8uD9CZh2OqlJNwap/zxsA0eg=; b=rZOHOH4wPuar9pCA4syJQ9iF60OMr7nAEyD+0o3QQP/wxqreylRz7OSikicQiZHyLD O6enByAyHxydMYEPyiq8D4j0fXh1MahX4/P5f73AmtPTUn4PABjTbl3DpBijpOJLkep1 1ScHrM+un3QtPGGzMzrqYGN2yvlR798Yli3GUGfilXJGj53CGmJ6hMvyo54XgO1ONDxe dSBPTmNqeJZiUNba36blsRV/EX50IQx0KBFxNk9QJ1qVRRvcJ9g3WH69kTgQqxScYvJj b34HNPWGTQP25V8+/3ZIhILnwzu5XccDP/tscpGvTuP6/epxej1awl4MtlpgNwUp7gbY 23Gg== X-Gm-Message-State: AOAM530tB0KW+zKhBydO0RHUp3SvleMy622tqiCiWo87Vkxp9wlF8Vs0 irUh9B7To1m1CnGvp7idtNKXUQ== X-Google-Smtp-Source: ABdhPJxOuyyS3LvoGAbBR4nUJilObnkpqgLOUglMCXGf/JCO+2pwwrm2IvHegCX8YX7eFM4vX26c6g== X-Received: by 2002:a05:620a:12ae:: with SMTP id x14mr4691354qki.25.1617821580011; Wed, 07 Apr 2021 11:53:00 -0700 (PDT) Received: from [192.168.1.132] ([177.194.41.149]) by smtp.gmail.com with ESMTPSA id j6sm16256306qtx.14.2021.04.07.11.52.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 Apr 2021 11:52:59 -0700 (PDT) Subject: Re: [PATCH] linux: sysconf: limit _SC_MAX_ARG to 6 MiB [BZ #25305] To: Florian Weimer Cc: Michal Nazarewicz , libc-alpha@sourceware.org, carlos@systemhalted.org References: <20210407151058.1176364-1-mina86@mina86.com> <6c926d3b-3094-f220-7777-91dacf975275@linaro.org> <878s5u7x9g.fsf@oldenburg.str.redhat.com> From: Adhemerval Zanella Message-ID: <5e390f1e-3c31-c4e9-aae0-168f0b4725c7@linaro.org> Date: Wed, 7 Apr 2021 15:52:57 -0300 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: <878s5u7x9g.fsf@oldenburg.str.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-6.5 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, 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: Wed, 07 Apr 2021 18:53:01 -0000 On 07/04/2021 15:41, Florian Weimer wrote: > * Adhemerval Zanella: > >> It is unfortunate that Linux did not provide a dynamic way to obtain >> this value, specially since it has changed over versions. So we will >> need to continue using heuristics. > > We can do a binary search using a test binary, perhaps the dynamic > linker itself. We can probe a few known values first to speed things > up, I guess. > > It's hideous, but given that the kernel doesn't support us here, what > else can we do? IMHO being conservative and use the lower bound of all supported kernels. I really don't think trying to be smart here with dynamic probing will add much, specially since this upper limit is what kernel will support from now on.