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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-47fd45a0ae0sm23010750f8f.33.2026.08.02.02.08.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 02 Aug 2026 02:08:09 -0700 (PDT) Date: Sun, 2 Aug 2026 10:08:08 +0100 From: David Laight To: "Chang S. Bae" Cc: , , , , , , , Omar Avelar , , Miguel Ojeda , Nathan Chancellor Subject: Re: [PATCH] x86/build/64: Prevent native builds from generating APX instructions Message-ID: <20260802100808.754400af@pumpkin> In-Reply-To: <2ea83400-a49e-4015-a0bd-926e5a0ef073@intel.com> References: <20260708211435.402426-1-chang.seok.bae@intel.com> <20260801124429.45d03af7@pumpkin> <2ea83400-a49e-4015-a0bd-926e5a0ef073@intel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 1 Aug 2026 17:00:36 -0700 "Chang S. Bae" wrote: > On 8/1/2026 4:44 AM, David Laight wrote: > > > > Much like when AVX support was added, -march-native needs to check that the > > operating system is saving the registers not that the cpu supports them. > > This GCC bug looks relevant: > > "__builtin_cpu_supports avx does not verify OS supports it" > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85100 Yes, except I thought it was much older... > The resulting commit 059cc8aca774 ("i386: Enable AVX/AVX512 features > only if supported by OSXSAVE") switched the compiler to read XCR0 before > set_feature(). > > Similarly, the APX enablement commit e686416b6217 ("[APX_EGPR] Initial > support for APX_F") extends the XCR0 check to determine whether APX is > usable. So, the compiler seemingly won't emit APX instructions without > OS setting XCR0.APX. Does that mean that this patch is completely unnecessary? David > > Thanks, > Chang