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Sun, 2 Aug 2026 00:00:38 +0000 Message-ID: <2ea83400-a49e-4015-a0bd-926e5a0ef073@intel.com> Date: Sat, 1 Aug 2026 17:00:36 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/build/64: Prevent native builds from generating APX instructions To: David Laight CC: , , , , , , , Omar Avelar , , Miguel Ojeda , Nathan Chancellor References: <20260708211435.402426-1-chang.seok.bae@intel.com> <20260801124429.45d03af7@pumpkin> Content-Language: en-US From: "Chang S. 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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 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. Thanks, Chang