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Sat, 30 May 2020 20:41:49 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4OdrZK2pGyMVHZP9dBAVdzAWc40dh9XQscP29VyVrvM=; b=HZvQiU2YlUtBkyi6j0X0sBvcK6 YZbb6RElwJlDvQSoI8EnGgMdqBHoihEOfco2ouCjUP4Lrt9K1yHxN8OR5Caaio7SnY2tGtjpu2vng jr1IQnGoevyNcal8I/kgEqEGTu3l+Zwlh5LVZwcZgiHGb4WD6ut/ABzyv8M2MhE68B0QNvidpnC3Q 2Lj81yDjMRBVamW438WZSQXqIyI6NJY97hDAeLt7m7VQQfHf4EELlTmQSzzKspRVXWPOK0cCOwljZ sJ9Nep2Dn0XzCi79koJwJFZzSkEGkTSq4HO0sQ6syXZ7aNRGYBeUxnVBXkgbEbKIIudGg/NB/2i+7 XqHaEaWg==; Received: from willy by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jf8IO-0000XW-Qx; Sat, 30 May 2020 20:41:32 +0000 Date: Sat, 30 May 2020 13:41:32 -0700 From: Matthew Wilcox To: Eric Biggers Message-ID: <20200530204132.GE19604@bombadil.infradead.org> References: <20200530060216.221456-1-ebiggers@kernel.org> <20200530171814.GD19604@bombadil.infradead.org> <20200530173547.GA12299@sol.localdomain> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200530173547.GA12299@sol.localdomain> X-Headers-End: 1jf8Ib-001F31-E6 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 10:35:47AM -0700, Eric Biggers wrote: > 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? void *memcpy_unsafe(void *dst, volatile void *src, __kernel_size_t); It can just call memcpy() of course, but the compiler can't reason about this function because it's not a stdlib function. _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel