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Mon, 21 Jun 2021 12:50:19 -0700 (PDT) Received: from [192.168.1.11] ([71.212.149.176]) by smtp.gmail.com with ESMTPSA id x7sm26853pjf.56.2021.06.21.12.50.18 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 21 Jun 2021 12:50:18 -0700 (PDT) Subject: Re: [PATCH 03/28] tcg/aarch64: Support bswap flags To: Peter Maydell References: <20210614083800.1166166-1-richard.henderson@linaro.org> <20210614083800.1166166-4-richard.henderson@linaro.org> <5a03a209-567a-df86-1b47-9cc39d82eb7b@linaro.org> From: Richard Henderson Message-ID: <48f4da88-7b3e-5ebb-7e10-c8d6528ac880@linaro.org> Date: Mon, 21 Jun 2021 12:50:17 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::434; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x434.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 6/21/21 12:40 PM, Peter Maydell wrote: > On Mon, 21 Jun 2021 at 19:12, Richard Henderson > wrote: >> >> On 6/21/21 7:01 AM, Peter Maydell wrote: >>> Side note: it's rather confusing that tcg_out_rev32() doesn't >>> emit a REV32 insn (it emits REV with sf==0). >> >> Which is REV with SF=0 also has OPC=10, which is REV32. > > No, REV32 has SF=1. The two operations are different: > > REV , -- swaps byte order of the bottom 32 bits > (zeroes the top half of Xd, as usual for Wn ops) > REV32 , -- swaps byte order of bottom 32 bits and > also swaps byte order of top 32 bits > (ie it is a 64-bit to 64-bit operation > which does does two bswap32()s) Ignore the assembler mnemonic and look at the opcode: REV Wd,Wn = SF=0, OPC=10 REV32 Xd,Xn = SF=1, OPC=10 REV Xd,Xn = SF=1, OPC=11 REV(Wd,Wd) = (uint32_t)REV32(Xd,Xd) i.e. the usual interpretation of sf=0. r~