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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38c2a1bb0d4sm11915942f8f.69.2025.01.27.09.27.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Jan 2025 09:27:37 -0800 (PST) Message-ID: <44f75f64-4480-4cd2-a907-cf0638568e55@linaro.org> Date: Mon, 27 Jan 2025 18:27:37 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] target/arm: Deprecate iwMMXt emulation and associated CPUs To: Peter Maydell , qemu-arm@nongnu.org, qemu-devel@nongnu.org References: <20250127112715.2936555-1-peter.maydell@linaro.org> Content-Language: en-US From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= In-Reply-To: <20250127112715.2936555-1-peter.maydell@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::42f; envelope-from=philmd@linaro.org; helo=mail-wr1-x42f.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, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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 27/1/25 12:27, Peter Maydell wrote: > This patchset marks all the CPUs that support iwMMXt as deprecated, > because I don't believe anybody is using them, and we have no way to > test the thousands of lines of code we have that's only there for > iwMMXt emulation. (See for instance the recent thread where a patch > was submitted to fix an issue detected by a static analyzer: we > didn't take it, largely because we had no way to know if the > behaviour change the patch would produce was correct or not.) > > The pxa2xx CPUs are now only useful with user-mode emulation, because > we dropped all the machine types that used them in 9.2. (Technically > you could alse use "-cpu pxa270" with a board model like versatilepb > which doesn't sanity-check the CPU type, but that has never been a > supported config.) > > To use them (or iwMMXt emulation) with QEMU user-mode you would need > to explicitly select them with the -cpu option or the QEMU_CPU > environment variable, because the '-cpu max' default CPU does not > include iwMMXt emulation. A google search finds no examples of > anybody doing this in the last decade. > > I asked some of the Linaro GCC folks if they were using QEMU to test > their iwMMXt codegen, or knew anybody doing that upstream, and the > answer was "no". In fact, GCC is in the process of dropping support > for iwMMXt entirely. > > We have one test case in check-tcg which purports to be checking > iwMMXt. In fact it is doing no such thing: it runs the test without > selecting an iwMMXt CPU, which means the iwMMXt insns are interpreted > as FPA11 insns by the linux-user emulate_arm_fpa11() code. So the test > prints garbage and then succeeds anyway. Modern distro toolchains Uh... > can't generate a binary that will run with -cpu pxa270 (because their > crt startup code uses Thumb insns); rather than putting in a lot of > effort trying to salvage the test case to really test a feature we've > deprecated, I opted to just remove the test. > > -- PMM > > Peter Maydell (2): > target/arm: deprecate the pxa2xx CPUs and iwMMXt emulation > tests/tcg/arm: Remove test-arm-iwmmxt test Series: Reviewed-by: Philippe Mathieu-Daudé