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Sun, 2 Aug 2026 21:32:34 +0000 Message-ID: <762ba2f6-bfe1-461d-a46d-84f5f368445b@intel.com> Date: Sun, 2 Aug 2026 14:32:32 -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> <2ea83400-a49e-4015-a0bd-926e5a0ef073@intel.com> <20260802100808.754400af@pumpkin> Content-Language: en-US From: "Chang S. 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It is necessary. On APX systems running, e.g. Linux kernel v6.16+, with the OS enables XCR0.APX, the compiler may consider all 32 registers usable and the compiled kernel inadvertently emits APX instructions (unconditionally) clobbering those registers. So -mno apxf prevents such unintended in-kernel use. Note that mainline currently supports only userspace APX, where user EGPR state is context-switched through the XSAVE mechanism. That alone is insufficient to support in-kernel uses. Like the legacy GPRs, EGPRs need to be handled on entry paths, and there are still many other things to consider before in-kernel usages. Thanks, Chang