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X-IronPort-AV: E=McAfee;i="6600,9927,11013"; a="15981633" X-IronPort-AV: E=Sophos;i="6.07,125,1708416000"; d="scan'208";a="15981633" Received: from orviesa001.jf.intel.com ([10.64.159.141]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Mar 2024 08:37:09 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,125,1708416000"; d="scan'208";a="49752855" Received: from laallen-mobl.amr.corp.intel.com (HELO [10.209.21.198]) ([10.209.21.198]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Mar 2024 08:37:09 -0700 Message-ID: Date: Thu, 14 Mar 2024 08:37:09 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/1] x86/elf: Add a new .note section containing Xfeatures information to x86 core files Content-Language: en-US To: Vignesh Balasubramanian , linux-kernel@vger.kernel.org, linux-toolchains@vger.kernel.org Cc: mpe@ellerman.id.au, npiggin@gmail.com, christophe.leroy@csgroup.eu, aneesh.kumar@kernel.org, naveen.n.rao@linux.ibm.com, ebiederm@xmission.com, keescook@chromium.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, bpetkov@amd.com, jinisusan.george@amd.com, matz@suse.de, binutils@sourceware.org, jhb@FreeBSD.org, felix.willgerodt@intel.com References: <20240314112359.50713-1-vigbalas@amd.com> <20240314112359.50713-2-vigbalas@amd.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: EC9F716001B X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: 5mks3hhrq3k4agwd9zq9byu3nwzwxbzy X-HE-Tag: 1710430630-971205 X-HE-Meta: U2FsdGVkX19GE48vPfht0I4oCXWBaiad5U82pyqpGTcrqrubEvLiEJ8cgmiXmFHZMLIEnremulKnCoMWL1vbSPqlAUoloTo4yRqaAD462N3aICd/tejiSugFgXyS7Nj3Itd5HrdniE/JrzibZ4JuXwLhAU//T8fTSdEQKogWlAq0ETZAsre0qDXO0pda7QXKW/3VXagau7VV9gRmPQBD2jSnHHNEyNgPCMBA/ihJk10rmtrp1jUJS4fnAn4eZzOCEHQ47ih3059DDled6d8h/q37N4+tHFvXGjgQm13bE4Df5fnUSC0zDAbLr85w+mTn+57OtGDQKd9cK62DyPGr8znAAUvIPomEatUR9RxtzVkYg4tlnD5ph/DW9AX+Wc3HN3TPy4Wt8FVSn1fQiQXk7yAh3ntuFWaKC1Che+Rzj1NU4w3p6aw5NOnfoTLYiG9GdmJIn+sPznHRl8gRhGUMwzG7Z8OEuXoBTloPHGKmlAyD9jvHzble1Myz7987Gqw3r1l1utSxTpVDUsMjgmBR3ndsvmsOPIYMKadkAkC6shKAZ37yxFO0/wQAkSa/InTPuUWFsdkROgniH2nSqBaGgG2mWjawoxNkEqL7JieYXlV37AXPsQBwFrOop7XX7C7mDP4AZ294l3vMWLUEMY2uPzZiXsfg8iLLCTX/uysZ/ZX2RBnthhksQ1p1VYxOjGgrmRi19t/s4nfARRufINUoVLHUOuLW8cb0FVn3gMj6u71VLYmCtkYA3jDMroRd2uKfDGXaT+EfkJYfRuS2zJq6hi/v8NmG7KT/ZSGwo2DoESjNQqrc70Cz+ZZgosNpqobnixK0nZeL9SzrDALOLic+mxeojM88E2VC3m04XoSU0KEFpKVX7xQKIREVbEyrN2huS0EKQLLhhIGmVn0RISg/ZV0L8rhbqvzbpNnjkp6UCb//x9lVWHu2D+9uWMd6Qk0ZNIXfrNX1FIrYD9YUd2s ATTYmkLO Gzs2HTnf397LwbdaaS0dgnDyUbiS7ItAwmKeMzKq9RlyDAxlFaeDXZR6Lr2Yh4r5bojj4aiuPF7gff/QlQFZY/VxP75BxCrVGlk10jKCZC2BT8//v3fmSKcL6UwZDeeKg72GlaJxokcry2J+PmgSVr30oVeQKUvAAtexMks+FXhSA15QvYXzVoHVdpb9pCio4MAAtbVPMdMKS+MUAZasWRwj4rVvNP17a9JvA07zKD3RV10IfkAlI8Ch3/4I5oug/sdHjRLAgo69DTQZhzxyhSdUKcgjA9a/weew5 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/14/24 04:23, Vignesh Balasubramanian wrote: > Add a new .note section containing type, size, offset and flags of > every xfeature that is present. Mechanically, I'd much rather have all of that info in the cover letter in the actual changelog instead. I'd also love to see a practical example of what an actual example core dump looks like on two conflicting systems: * Total XSAVE size * XCR0 value * XSTATE_BV from the core dump * XFEATURE offsets for each feature Do you have any information about what other OSes are doing in this area? I thought Windows, for instance, was even less flexible about the XSAVE format than Linux is. Why didn't LWP cause this problem? >From the cover letter: > But this patch series depends on heuristics based on the total XSAVE > register set size and the XCR0 mask to infer the layouts of the > various register blocks for core dumps, and hence, is not a foolproof > mechanism to determine the layout of the XSAVE area. It may not be theoretically foolproof. But I'm struggling to think of a case where it would matter in practice. Is there any CPU from any vendor where this is actually _needed_? Sure, it's ugly as hell, but these notes aren't going to be available universally _ever_, so it's not like the crummy heuristic code gets to go away. Have you seen the APX spec? > https://www.intel.com/content/www/us/en/developer/articles/technical/advanced-performance-extensions-apx.html It makes this even more fun because it adds a new XSAVE state component, but reuses the MPX offsets. > This information will be used by the debuggers to understand the XSAVE > layout of the machine where the core file is dumped, and to read XSAVE > registers, especially during cross-platform debugging. This is pretty close to just a raw dump of the XSAVE CPUID leaves. Rather than come up with an XSAVE-specific ABI that depends on CPUID *ANYWAY* (because it dumps the "flags" register aka. ECX), maybe we should just bite the bullet and dump out (some of) the raw CPUID space.