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=-7.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 622BBC282CA for ; Wed, 13 Feb 2019 01:41:22 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 300B72190A for ; Wed, 13 Feb 2019 01:41:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="RcDzKGbf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 300B72190A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=I7O4tNTIgQTSSbDnT8g9uvUzor1MeUaucWBkogfRkug=; b=RcDzKGbfJuZjRa XXYbq7J15CnHVm1wHQ+0jQ/Lqeyd+IPFEWTKl5S7RtIgFFxTJk59uHrDdMK7ge9FfeJwdq3OZpGjl M0MTclrvIw/xMowzVjjByTmzTPY1xcruBh2wo4oYvCei4AuyKJd5m6eHS/DfIpmUzSaBCighzKJcH qWaPOT27o8mVJ35Li2J8+Ou1DwZpbRnKYPV4DllEozcUkQrXZNHDHVL2QHUZtYegi9XQnTc1RZHnM xBGD8XkriA/+rApMYBQPYnJHMYCksYZwCTiwGou0i8TXp9Ln2zYku+JSwNz3uPMGEf5j7Ptg038ei 6Tm4ETzbCP2ohZzTKRQQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtjY7-0000Yg-Li; Wed, 13 Feb 2019 01:41:19 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gtjY4-0000YH-Ll; Wed, 13 Feb 2019 01:41:18 +0000 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0C4402190A; Wed, 13 Feb 2019 01:41:14 +0000 (UTC) Date: Tue, 12 Feb 2019 20:41:13 -0500 From: Steven Rostedt To: Mars Cheng Subject: Re: [PATCH 1/1] tracing: Fix event_trace_printk loss on printk_format. Message-ID: <20190212204113.5ecaa2a1@gandalf.local.home> In-Reply-To: <1549971717-4693-1-git-send-email-mars.cheng@mediatek.com> References: <1549971717-4693-1-git-send-email-mars.cheng@mediatek.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190212_174116_728462_DB904EC4 X-CRM114-Status: GOOD ( 21.27 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Andress Kuo , CC Hwang , linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 12 Feb 2019 19:41:57 +0800 Mars Cheng wrote: > From: Andress Kuo > > If fmt on event_trace_printk is not a constant, It means that something not > guaranteed, so the compiler optimizes the fmt out, and then the > __trace_printk_fmt section is not filled. if __trace_printk_fmt is not > filled, the kernel will not allocate the special buffers needed for the > event_trace_printk() and then not shown in the file output > sys/kernel/debug/tracing/print_formats. > > Adding a "__used" to the variable in the __trace_printk_fmt section on > event_trace_printk() will keep it around, even though it is set to NULL. > This will keep the string from being printed in the > sys/kernel/debug/tracing/printk_formats section. > > We can also refer to commit 3debb0a9ddb1 ("tracing: Fix trace_printk() > to print when not using bprintk()")that it had similar issue on path of > trace_printk(). Honestly, I don't even remember why that macro was created. I think it's a remnant from the creation of the trace events. I think the best solution is just to nuke it. It shouldn't be used anymore. I'll dig a bit deeper into the history of that macro, but I'm thinking it shouldn't exist anymore. [ /me returns from walking down memory lane ] Wow, that brings back some wild memories. Yes, that macro must die, and I wish the history of it could die along with it ;-) The horror of the old ways I tell you. The event_trace_printk() was the original way we displayed events! No real formatting, no parsing my userspace tools. It was just a glamorized printk. It was called TRACE_FORMAT() which was deprecated by today's TRACE_EVENT(). That macro should have been removed by commit b8e65554d80b4. Please just send a patch to delete that macro. Let's not be maintaining it. It gives me nightmares. -- Steve > > Signed-off-by: Andress Kuo > Signed-off-by: Mars Cheng > --- > include/linux/trace_events.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h > index 8a62731..26bd7c4 100644 > --- a/include/linux/trace_events.h > +++ b/include/linux/trace_events.h > @@ -551,7 +551,7 @@ extern int trace_define_field(struct trace_event_call *call, const char *type, > __trace_printk_check_format(fmt, ##args); \ > tracing_record_cmdline(current); \ > if (__builtin_constant_p(fmt)) { \ > - static const char *trace_printk_fmt \ > + static const char *trace_printk_fmt __used \ > __attribute__((section("__trace_printk_fmt"))) = \ > __builtin_constant_p(fmt) ? fmt : NULL; \ > \ _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel