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Sat, 30 May 2020 17:36:06 +0000 Received: from sol.localdomain (c-107-3-166-239.hsd1.ca.comcast.net [107.3.166.239]) (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 71A3C20774; Sat, 30 May 2020 17:35:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1590860148; bh=Km+qsBMMCDWbNMm6RhJqYLEma5l3VL5pC1iVxzc9Ljc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=ONHZOgZx3Q3+kUxk28asW/VTjbkXr6fmbkaCLfRocfasre//eQ8N+H8ow5bFn2xpc uzOcmb+LeGzNgVi+kWs1F9TLCQo0V1V/Cx5r4MEnnaZoz/2+E51ez9VyjQ8BaL47rD 3JZWi+c4WkS0ahXTI7RyIR2JEJ4iTPJZ2z9GX+tM= Date: Sat, 30 May 2020 10:35:47 -0700 From: Eric Biggers To: Matthew Wilcox Message-ID: <20200530173547.GA12299@sol.localdomain> References: <20200530060216.221456-1-ebiggers@kernel.org> <20200530171814.GD19604@bombadil.infradead.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200530171814.GD19604@bombadil.infradead.org> X-Headers-End: 1jf5Op-0018Hr-6A Subject: Re: [f2fs-dev] [PATCH] ext4: avoid utf8_strncasecmp() with unstable name X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Daniel Rosenberg , stable@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Al Viro , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, Gabriel Krisman Bertazi Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On Sat, May 30, 2020 at 10:18:14AM -0700, Matthew Wilcox wrote: > On Fri, May 29, 2020 at 11:02:16PM -0700, Eric Biggers wrote: > > + if (len <= DNAME_INLINE_LEN - 1) { > > + unsigned int i; > > + > > + for (i = 0; i < len; i++) > > + strbuf[i] = READ_ONCE(str[i]); > > + strbuf[len] = 0; > > This READ_ONCE is going to force the compiler to use byte accesses. > What's wrong with using a plain memcpy()? > It's undefined behavior when the source can be concurrently modified. Compilers can assume that it's not, and remove the memcpy() (instead just using the source data directly) if they can prove that the destination array is never modified again before it goes out of scope. Do you have any suggestions that don't involve undefined behavior? - Eric _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel