From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gproxy4-pub.mail.unifiedlayer.com (gproxy4-pub.mail.unifiedlayer.com [69.89.23.142]) by sourceware.org (Postfix) with ESMTPS id 36B113858C53 for ; Tue, 7 Mar 2023 21:57:06 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 36B113858C53 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=tromey.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tromey.com Received: from cmgw15.mail.unifiedlayer.com (unknown [10.0.90.130]) by progateway6.mail.pro1.eigbox.com (Postfix) with ESMTP id 9E40510064D92 for ; Tue, 7 Mar 2023 21:57:05 +0000 (UTC) Received: from box5379.bluehost.com ([162.241.216.53]) by cmsmtp with ESMTP id ZfIvpB2ep9Qs9ZfIvpmY0G; Tue, 07 Mar 2023 21:57:05 +0000 X-Authority-Reason: nr=8 X-Authority-Analysis: v=2.4 cv=PJbKRdmC c=1 sm=1 tr=0 ts=6407b331 a=ApxJNpeYhEAb1aAlGBBbmA==:117 a=ApxJNpeYhEAb1aAlGBBbmA==:17 a=dLZJa+xiwSxG16/P+YVxDGlgEgI=:19 a=k__wU0fu6RkA:10:nop_rcvd_month_year a=Qbun_eYptAEA:10:endurance_base64_authed_username_1 a=CCpqsmhAAAAA:8 a=iADw-I3MGZSWPc7TGlMA:9 a=ul9cdbp4aOFLsgKbc677:22 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tromey.com; s=default; h=Content-Type:MIME-Version:Message-ID:In-Reply-To:Date:References :Subject:Cc:To:From:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=XdpONquEmMtVis4GawzZKBmBY1zloLgeVwUoYmbfDPo=; b=X2qSmiWdd4XEE6JmdfuftR+DYC +lL3nbLdwNnDW/kxDpWngFhIdazR3TrE7Ekcs/S9xW2soEQXThAYIe8hRIh5jHC+HcgrB/GNT8/24 hJOJmD3B2+r+LvFJDm566ddjN; Received: from 75-166-130-93.hlrn.qwest.net ([75.166.130.93]:41004 helo=murgatroyd) by box5379.bluehost.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1pZfIv-0031Dr-C3; Tue, 07 Mar 2023 14:57:05 -0700 From: Tom Tromey To: Simon Marchi via Gdb-patches Cc: Andrew Burgess , Simon Marchi Subject: Re: [PATCH 00/13] Remove a bunch of alloca uses References: X-Attribution: Tom Date: Tue, 07 Mar 2023 14:57:03 -0700 In-Reply-To: (Simon Marchi via Gdb-patches's message of "Mon, 27 Feb 2023 21:47:55 -0500") Message-ID: <87fsagp6mo.fsf@tromey.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - box5379.bluehost.com X-AntiAbuse: Original Domain - sourceware.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - tromey.com X-BWhitelist: no X-Source-IP: 75.166.130.93 X-Source-L: No X-Exim-ID: 1pZfIv-0031Dr-C3 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 75-166-130-93.hlrn.qwest.net (murgatroyd) [75.166.130.93]:41004 X-Source-Auth: tom+tromey.com X-Email-Count: 6 X-Source-Cap: ZWx5bnJvYmk7ZWx5bnJvYmk7Ym94NTM3OS5ibHVlaG9zdC5jb20= X-Local-Domain: yes X-Spam-Status: No, score=-3020.6 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,JMQ_SPF_NEUTRAL,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: >>>>> "Simon" == Simon Marchi via Gdb-patches writes: Simon> Every time I spot an alloca in the wild, I'm also tempted to switch it Simon> to vector or something like that. But then I think, it's an extra Simon> dynamic allocation for no real gain, so it would just make things worse. I'd imagine these allocations probably don't matter in most cases, but on the other hand, alloca is a hazard, as it's easy to accidentally blow up the stack. Simon> When we know the maximum size a buffer can have, instead of using Simon> alloca, it would better to statically allocate that size on the stack, Simon> and then user an array_view to define the effectively used portion of Simon> it. True, and for registers in particular we could just have a #define somewhere probably. At least, assuming they have some maximum size across all supported arches. Simon> If the license allows, I'd be all for just importing an existing Simon> implementation in our code base, to avoid reinventing the wheel. This would also be fine with me but I tend to think in most cases it's probably unnecessary. Like, I wouldn't blink if new code came in using a local vector<> but I might mention a new alloca in a review. Tom