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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 4F753C38A2A for ; Fri, 8 May 2020 12:02:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 258E521582 for ; Fri, 8 May 2020 12:02:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="ubfbVMHF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727111AbgEHMCi (ORCPT ); Fri, 8 May 2020 08:02:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53162 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1726618AbgEHMCh (ORCPT ); Fri, 8 May 2020 08:02:37 -0400 Received: from mail-lf1-x143.google.com (mail-lf1-x143.google.com [IPv6:2a00:1450:4864:20::143]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4CDFFC05BD43 for ; Fri, 8 May 2020 05:02:37 -0700 (PDT) Received: by mail-lf1-x143.google.com with SMTP id b26so1209473lfa.5 for ; Fri, 08 May 2020 05:02:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=lNKVrkJdHzfMbK2WFg5Y7tu/Zp5ibf2iNC5EM1tQRJo=; b=ubfbVMHFvkGFqi6/lMGAmUyGcg20V5yh8C00LQp7ohCZxq2z4EmwwX3B73H8EZ7Y6+ aJCVbMOvPuRCut0Bnl8ET5c2XfZXweuNYjo3brQ6CEYILBG8HhEgVuhFWVWA1BmL+7wr PaMOGT8qiPBOFsYR+vprL3K/7EVvJ8oJXMBygdJ6uGjhciK55QG7biHSQuFnHCtyvZe5 srhzCTXCfW52nQOZMKMQqUcLd8x7Ffk6Kk/ZsU0oOHDAWkNAqGX1e8h1hy8E4RAfCjEQ 6gCD/cXPSscJnlWgSBvvUILe/g9S3+oDCA5v+IgSinV7FqAm/oZSQvwlhvdPaLD8bWMp QpoQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=lNKVrkJdHzfMbK2WFg5Y7tu/Zp5ibf2iNC5EM1tQRJo=; b=jt5T2pwbkIemVv8rKA16OwkyDfrU/+p9bDtLKvVdzImOJToB0yhWFtxxx9dwaZ71mi ckX/3hQ/mthYGnmD5Rre0Wd2uHEghx05tPTUQMWlWu0vc6TP9RyzSM8oecDSyuGYBklQ 9nLKLFWIMH3QOpFrrfLqp9nrZz570AUTFDlKeU8sUdhltvmaD2Segc52nUGN2IpfYbuv TxeHeaDgtJ7CDSKQKIK/TR0+L2WCGpGX1ZItTev2ogjH0lT94EAyKsR6vdZa+exe545g Bgu60HnRtZlDq9+xJkckPtcV2EG7bilwk2vgInYK+2j2lx7STMkSQrtdgF/BAylcFN7b cOOA== X-Gm-Message-State: AOAM530LdvhDd9OANJ6/3F1QmPj0GorCULNZZ1A3aBsTYY6Ujdntc9a9 arW5qHlnhkQDNY1fJ9TJZnD8+FiuSP/STfJnV/dw2Q== X-Google-Smtp-Source: ABdhPJwC7HcQZBmnzQTCK4sgJwvhh1shXjGpCyyI6P2ffCkh7V87ZwnoziPmO0iHtAk8wnYX7eQKeQNhe8U2VKMv2Qo= X-Received: by 2002:a19:ccce:: with SMTP id c197mr1688763lfg.59.1588939355636; Fri, 08 May 2020 05:02:35 -0700 (PDT) MIME-Version: 1.0 References: <20200507161125.1.I2cce9ac66e141230c3644b8174b6c15d4e769232@changeid> In-Reply-To: <20200507161125.1.I2cce9ac66e141230c3644b8174b6c15d4e769232@changeid> From: Sumit Garg Date: Fri, 8 May 2020 17:32:24 +0530 Message-ID: Subject: Re: [PATCH] kdb: Cleanup math with KDB_CMD_HISTORY_COUNT To: Douglas Anderson Cc: Jason Wessel , Daniel Thompson , Chuhong Yuan , Dan Carpenter , Masahiro Yamada , kgdb-bugreport@lists.sourceforge.net, Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 8 May 2020 at 04:42, Douglas Anderson wrote: > > From code inspection the math in handle_ctrl_cmd() looks super sketchy > because it subjects -1 from cmdptr and then does a "% > KDB_CMD_HISTORY_COUNT". It turns out that this code works because > "cmdptr" is unsigned and KDB_CMD_HISTORY_COUNT is a nice power of 2. > Let's make this a little less sketchy. > > This patch should be a no-op. > > Signed-off-by: Douglas Anderson > --- > Reviewed-by: Sumit Garg > kernel/debug/kdb/kdb_main.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c > index 515379cbf209..6865a0f58d38 100644 > --- a/kernel/debug/kdb/kdb_main.c > +++ b/kernel/debug/kdb/kdb_main.c > @@ -1108,7 +1108,8 @@ static int handle_ctrl_cmd(char *cmd) > switch (*cmd) { > case CTRL_P: > if (cmdptr != cmd_tail) > - cmdptr = (cmdptr-1) % KDB_CMD_HISTORY_COUNT; > + cmdptr = (cmdptr + KDB_CMD_HISTORY_COUNT - 1) % > + KDB_CMD_HISTORY_COUNT; > strscpy(cmd_cur, cmd_hist[cmdptr], CMD_BUFLEN); > return 1; > case CTRL_N: > -- > 2.26.2.645.ge9eca65c58-goog >