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Tue, 01 Dec 2020 07:55:22 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 14557AC2F; Tue, 1 Dec 2020 07:55:22 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d5b2c199-83e1-4d7e-92fe-95a6614cf103 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1606809322; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VQbGmZorjHVggPDNorqVk7pQ8bzwkxtNEbHZ9tsGUkg=; b=NvEaPa/nN/uNhHGiOmVDqIlZUgJFvgL7jhpCk6ym0fx5P7GiS2GnR2QCgg5XmZkeiimY3T 0CuYaq35JlsDHBUHQHDCadrKu+i9bo6sVQjAOe+VW4FNj6q07Nl33d7+0UgMSniFPYRWP/ UsvZY7BjFphOsFLRf+ag7lEDiOWWPhE= Subject: Re: [PATCH V3 19/23] xen/arm: io: Abstract sign-extension To: Oleksandr Cc: "xen-devel@lists.xenproject.org" , Oleksandr Tyshchenko , Stefano Stabellini , Julien Grall , Julien Grall , Volodymyr Babchuk References: <1606732298-22107-1-git-send-email-olekstysh@gmail.com> <1606732298-22107-20-git-send-email-olekstysh@gmail.com> <878sai7e1a.fsf@epam.com> From: Jan Beulich Message-ID: <93284ea1-e658-ffff-3223-174d633e38ad@suse.com> Date: Tue, 1 Dec 2020 08:55:22 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 01.12.2020 00:27, Oleksandr wrote: > On 30.11.20 23:03, Volodymyr Babchuk wrote: >> Oleksandr Tyshchenko writes: >>> --- a/xen/include/asm-arm/traps.h >>> +++ b/xen/include/asm-arm/traps.h >>> @@ -83,6 +83,30 @@ static inline bool VABORT_GEN_BY_GUEST(const struct cpu_user_regs *regs) >>> (unsigned long)abort_guest_exit_end == regs->pc; >>> } >>> >>> +/* Check whether the sign extension is required and perform it */ >>> +static inline register_t sign_extend(const struct hsr_dabt dabt, register_t r) >>> +{ >>> + uint8_t size = (1 << dabt.size) * 8; >>> + >>> + /* >>> + * Sign extend if required. >>> + * Note that we expect the read handler to have zeroed the bits >>> + * outside the requested access size. >>> + */ >>> + if ( dabt.sign && (r & (1UL << (size - 1))) ) >>> + { >>> + /* >>> + * We are relying on register_t using the same as >>> + * an unsigned long in order to keep the 32-bit assembly >>> + * code smaller. >>> + */ >>> + BUILD_BUG_ON(sizeof(register_t) != sizeof(unsigned long)); >>> + r |= (~0UL) << size; >> If `size` is 64, you will get undefined behavior there. > I think, we don't need to worry about undefined behavior here. Having > size=64 would be possible with doubleword (dabt.size=3). But if "r" > adjustment gets called (I mean Syndrome Sign Extend bit is set) then > we deal with byte, halfword or word operations (dabt.size<3). Or I > missed something? At which point please put in a respective ASSERT(), possibly amended by a brief comment. Jan