From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 29323C4332B for ; Thu, 19 Mar 2020 02:00:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0AFF2071C for ; Thu, 19 Mar 2020 02:00:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="AWbpJB7y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727137AbgCSCAG (ORCPT ); Wed, 18 Mar 2020 22:00:06 -0400 Received: from mail-ot1-f65.google.com ([209.85.210.65]:39935 "EHLO mail-ot1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726596AbgCSCAG (ORCPT ); Wed, 18 Mar 2020 22:00:06 -0400 Received: by mail-ot1-f65.google.com with SMTP id r2so796681otn.6 for ; Wed, 18 Mar 2020 19:00:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=imF7ST2MLfxUreXaGENTzkNj4f/nZW7foh0Y9cYT5II=; b=AWbpJB7yskPqnyMVt/2INrUoBmCiE9QQmUJNQ5HmlLZf+VrMgdb+7MhMYLp69fSjxZ Aq05ZnGQr1YBsjjpAv0+efatsfSJIuXdIun5mVUNoDtoPik4BXavpFZrxPpr9J2g9dF2 H8bN+wKhuXrg3XlaN02nEb8JTMKV+ss/UnaGSXv5Kc4/jzcvUDy9xn2uCbpQ2xAb1Y0I Cj0oPyH1BO1UdCN/9vHfMKrGMlctVQsW9iZGCXEeL3XDTAVqD0PbfZD4N9NyqrnJkzLC 9jUhqecW9jZSntnRvwVuhDc3n6bgHtb5ZZTSIQSQ71GEM6gKWYMF4iAZTfJ8pGXuSP4s KThg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=imF7ST2MLfxUreXaGENTzkNj4f/nZW7foh0Y9cYT5II=; b=eD2hv2tH9+W6McAbHfpDxrvWnK0/6FvMQGnnpJpJRzxQ9Q8TJN2HKNYhLLKm0JHkgS LqlRY9vo5R7fZFWLqOfkGr+6Sv6v58zu0O6uWAUPfu2nlIzXj1TkGrvoidMe+qHXbukD xKEjsKdWFs/R0sF/E5zoJ01uIOf163q4fplLV9OywdtOn0KLm6EVEQ3kK/IYa/GSrds/ SjjisIO4qGSiiJNMFNjrgeA+EqzteXOEPL4zPhj1wOi8tEikG+42GINlon28iPgvaxsd 34KsQxeZCO08zPF67KDIi+1LNnWBNaVnXYaAJhpWKhlioTBOLix7qOGf97FRR1rslmgO nggQ== X-Gm-Message-State: ANhLgQ3GYhvs09YNAynzC7wL754pRPd/DFdOY+805E5ofRp5IeVQ2QKR G7OFyJ9HnC2XAswv78jQuUw= X-Google-Smtp-Source: ADFU+vswIHfUXvQfBu1NxP8p4+z8IJUMGHuTCJlToMmDF6UlG4GRrhcbHrElvXRNZyM1FrMupU+VtA== X-Received: by 2002:a9d:65ca:: with SMTP id z10mr509809oth.86.1584583205893; Wed, 18 Mar 2020 19:00:05 -0700 (PDT) Received: from ubuntu-m2-xlarge-x86 ([2604:1380:4111:8b00::1]) by smtp.gmail.com with ESMTPSA id q22sm331243oic.22.2020.03.18.19.00.05 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 18 Mar 2020 19:00:05 -0700 (PDT) Date: Wed, 18 Mar 2020 19:00:04 -0700 From: Nathan Chancellor To: Steven Rostedt , Ingo Molnar Cc: linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, Nick Desaulniers Subject: Re: [PATCH v2] tracing: Use address-of operator on section symbols Message-ID: <20200319020004.GB8292@ubuntu-m2-xlarge-x86> References: <20200220051011.26113-1-natechancellor@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200220051011.26113-1-natechancellor@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 19, 2020 at 10:10:12PM -0700, Nathan Chancellor wrote: > Clang warns: > > ../kernel/trace/trace.c:9335:33: warning: array comparison always > evaluates to true [-Wtautological-compare] > if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt) > ^ > 1 warning generated. > > These are not true arrays, they are linker defined symbols, which are > just addresses. Using the address of operator silences the warning and > does not change the runtime result of the check (tested with some print > statements compiled in with clang + ld.lld and gcc + ld.bfd in QEMU). > > Link: https://github.com/ClangBuiltLinux/linux/issues/893 > Suggested-by: Nick Desaulniers > Signed-off-by: Nathan Chancellor > --- > > v1 -> v2: https://lore.kernel.org/lkml/20200219045423.54190-4-natechancellor@gmail.com/ > > * No longer a series because there is no prerequisite patch. > * Use address-of operator instead of casting to unsigned long. > > NOTE: The code generation does seem to change, unlike every other call > site that I did this change to but the result of the check remains the > same as noted in the commit message and I cannot really understand what > has changed in the assembly. Please let me know if there is something > catastrophically wrong. > > kernel/trace/trace.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index c797a15a1fc7..78727dd9a6f5 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -9332,7 +9332,7 @@ __init static int tracer_alloc_buffers(void) > goto out_free_buffer_mask; > > /* Only allocate trace_printk buffers if a trace_printk exists */ > - if (__stop___trace_bprintk_fmt != __start___trace_bprintk_fmt) > + if (&__stop___trace_bprintk_fmt != &__start___trace_bprintk_fmt) > /* Must be called before global_trace.buffer is allocated */ > trace_printk_init_buffers(); > > -- > 2.25.1 > Gentle ping for review/acceptance. Cheers, Nathan