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Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH v2 02/30] include/exec/memop: Add bits describing atomicity Content-Language: en-US To: Richard Henderson , qemu-devel@nongnu.org References: <20230216025739.1211680-1-richard.henderson@linaro.org> <20230216025739.1211680-3-richard.henderson@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: <20230216025739.1211680-3-richard.henderson@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::32e; envelope-from=philmd@linaro.org; helo=mail-wm1-x32e.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=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 16/2/23 03:57, Richard Henderson wrote: > These bits may be used to describe the precise atomicity > requirements of the guest, which may then be used to > constrain the methods by which it may be emulated by the host. > > For instance, the AArch64 LDP (32-bit) instruction changes > semantics with ARMv8.4 LSE2, from > > MO_64 | MO_ATMAX_4 | MO_ATOM_IFALIGN > (64-bits, single-copy atomic only on 4 byte units, > nonatomic if not aligned by 4), > > to > > MO_64 | MO_ATMAX_SIZE | MO_ATOM_WITHIN16 > (64-bits, single-copy atomic within a 16 byte block) > > The former may be implemented with two 4 byte loads, or > a single 8 byte load if that happens to be efficient on > the host. The latter may not, and may also require a > helper when misaligned. > > Signed-off-by: Richard Henderson > --- > include/exec/memop.h | 36 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 36 insertions(+) Reviewed-by: Philippe Mathieu-Daudé