From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 194B3C02198 for ; Mon, 10 Feb 2025 22:10:48 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.885006.1294765 (Exim 4.92) (envelope-from ) id 1thbz4-0002ID-T5; Mon, 10 Feb 2025 22:10:30 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 885006.1294765; Mon, 10 Feb 2025 22:10:30 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1thbz4-0002I6-QR; Mon, 10 Feb 2025 22:10:30 +0000 Received: by outflank-mailman (input) for mailman id 885006; Mon, 10 Feb 2025 22:10:28 +0000 Received: from se1-gles-sth1-in.inumbo.com ([159.253.27.254] helo=se1-gles-sth1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1thbz2-0002Hr-RV for xen-devel@lists.xenproject.org; Mon, 10 Feb 2025 22:10:28 +0000 Received: from mail-wm1-x341.google.com (mail-wm1-x341.google.com [2a00:1450:4864:20::341]) by se1-gles-sth1.inumbo.com (Halon) with ESMTPS id d5705649-e7fb-11ef-a075-877d107080fb; Mon, 10 Feb 2025 23:10:27 +0100 (CET) Received: by mail-wm1-x341.google.com with SMTP id 5b1f17b1804b1-4364a37a1d7so48684355e9.3 for ; Mon, 10 Feb 2025 14:10:27 -0800 (PST) Received: from [192.168.1.10] (host-92-26-98-202.as13285.net. [92.26.98.202]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4391dfd8448sm158665005e9.38.2025.02.10.14.10.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 10 Feb 2025 14:10:26 -0800 (PST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: d5705649-e7fb-11ef-a075-877d107080fb DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.com; s=google; t=1739225427; x=1739830227; darn=lists.xenproject.org; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:from:to:cc:subject:date:message-id:reply-to; bh=lCmXPP/SRDMorkAy5nlfgjxuqK5K8X0YKMp2DhtqBoE=; b=cIjsGiPbIMkdeQECHHIzLWkQTvWoMv9PSiGBGa/uwkZblxDPtEHSBKZn7rI2tXvk9F JYQVJV60oBWyqBs3+mQ24fPyxFMFEVZC9TiX19zocDFk0CmE1S2sNhPyRtu316pJ/d30 I+kSgNwQZHHVb1XPop3GPTkWI16BiStuS20wk= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1739225427; x=1739830227; h=content-transfer-encoding:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=lCmXPP/SRDMorkAy5nlfgjxuqK5K8X0YKMp2DhtqBoE=; b=ZMx6rlzltU8S3faUtt9zOafiu9CrAA+P710UAVteHEr3U0ZWXPi3XCETSpNo0HPFGO noOK7x22UI5uqft1ay1IjOClH2o0OYFRXmPjnip8L3AyHl0DZbvH8FFXu4ebzYppKpe+ Wk/sahkPne6/DcBUl6x2M1u8WokhQNMrPzHaTzVXN61IfaQLGWep/RDo6piqnDoJiYYp HIAAPB7Evec3fbZjVLSQp2MGh5aXcrMoUrPM3g21HLa4H3XNMI5MfV7ztYxspcUgJx4F q93p1B9OEn/HSEk/iGDahc5PF+1v1/UeHAieQFFk6k+MTAKkvbcSjqpmTsgGn6rzg3eb 2mhQ== X-Forwarded-Encrypted: i=1; AJvYcCXc6qlBvzS66HidHRwwcUI3jm/K/Y5YgHqXhMAHfAVf9en7bHvATjE4fgyiw5e5ODHCpFWoZvb7Yg4=@lists.xenproject.org X-Gm-Message-State: AOJu0YzoZd+zj6UcDwgn5hw8TG5amR9hL8ijezmvZ5XlSUbjdamVKoP/ 74eFEey7Om+B93cmHmnkRN8J1SjcGK3MEDM/p8qA5ablpIUy5yunsa0KSfcxDro= X-Gm-Gg: ASbGncu0bYbv1RZervzrITeIl2iJsL9wchGdzSltsJH8N1xqUDt1nBIAX1jhcxKoQd5 WN7cKkPgISYNmbtDWCIe+rzuNelqGdLmYH/pw0OgknMEmU3t7QHvE/gI3r5YgXhzuq6WIgE0Tg1 yubickUYZCrhclws8CLQRnwXjR4sIpULdLILSZT8o9SyELEMlJQvtNrqJ70pZGsYnpqms/ESt6a aQgsuZ9ZHj7mXd74rEl8cgpvkcHiM6fEG5vOfiBOgjNIyZr+It36Q52iPu/CXsaOx/OOCxDrUIP 0dARg8EDvWrXZDNLAre3EXOCQwDNX2vg3lTdY8kT+cdElJW+kii/4SQ= X-Google-Smtp-Source: AGHT+IHqLxiEAxNJ3UreZRwS2XiPKHB/0xwaWxU4DH17EPfUuBqt4OsawBMLZMPmGs0KpmZTLgktDQ== X-Received: by 2002:a05:600c:1f85:b0:436:30e4:459b with SMTP id 5b1f17b1804b1-4392499962dmr134942205e9.18.1739225427142; Mon, 10 Feb 2025 14:10:27 -0800 (PST) Message-ID: Date: Mon, 10 Feb 2025 22:10:26 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 2/4] ARM: Fix register constraints in run_in_exception_handler() To: Julien Grall , Xen-devel Cc: Stefano Stabellini , Volodymyr Babchuk , Bertrand Marquis , Michal Orzel , Oleksii Kurochko References: <20250208000256.431883-1-andrew.cooper3@citrix.com> <20250208000256.431883-3-andrew.cooper3@citrix.com> Content-Language: en-GB From: Andrew Cooper Autocrypt: addr=andrew.cooper3@citrix.com; keydata= xsFNBFLhNn8BEADVhE+Hb8i0GV6mihnnr/uiQQdPF8kUoFzCOPXkf7jQ5sLYeJa0cQi6Penp VtiFYznTairnVsN5J+ujSTIb+OlMSJUWV4opS7WVNnxHbFTPYZVQ3erv7NKc2iVizCRZ2Kxn srM1oPXWRic8BIAdYOKOloF2300SL/bIpeD+x7h3w9B/qez7nOin5NzkxgFoaUeIal12pXSR Q354FKFoy6Vh96gc4VRqte3jw8mPuJQpfws+Pb+swvSf/i1q1+1I4jsRQQh2m6OTADHIqg2E ofTYAEh7R5HfPx0EXoEDMdRjOeKn8+vvkAwhviWXTHlG3R1QkbE5M/oywnZ83udJmi+lxjJ5 YhQ5IzomvJ16H0Bq+TLyVLO/VRksp1VR9HxCzItLNCS8PdpYYz5TC204ViycobYU65WMpzWe LFAGn8jSS25XIpqv0Y9k87dLbctKKA14Ifw2kq5OIVu2FuX+3i446JOa2vpCI9GcjCzi3oHV e00bzYiHMIl0FICrNJU0Kjho8pdo0m2uxkn6SYEpogAy9pnatUlO+erL4LqFUO7GXSdBRbw5 gNt25XTLdSFuZtMxkY3tq8MFss5QnjhehCVPEpE6y9ZjI4XB8ad1G4oBHVGK5LMsvg22PfMJ ISWFSHoF/B5+lHkCKWkFxZ0gZn33ju5n6/FOdEx4B8cMJt+cWwARAQABzSlBbmRyZXcgQ29v cGVyIDxhbmRyZXcuY29vcGVyM0BjaXRyaXguY29tPsLBegQTAQgAJAIbAwULCQgHAwUVCgkI CwUWAgMBAAIeAQIXgAUCWKD95wIZAQAKCRBlw/kGpdefoHbdD/9AIoR3k6fKl+RFiFpyAhvO 59ttDFI7nIAnlYngev2XUR3acFElJATHSDO0ju+hqWqAb8kVijXLops0gOfqt3VPZq9cuHlh IMDquatGLzAadfFx2eQYIYT+FYuMoPZy/aTUazmJIDVxP7L383grjIkn+7tAv+qeDfE+txL4 SAm1UHNvmdfgL2/lcmL3xRh7sub3nJilM93RWX1Pe5LBSDXO45uzCGEdst6uSlzYR/MEr+5Z JQQ32JV64zwvf/aKaagSQSQMYNX9JFgfZ3TKWC1KJQbX5ssoX/5hNLqxMcZV3TN7kU8I3kjK mPec9+1nECOjjJSO/h4P0sBZyIUGfguwzhEeGf4sMCuSEM4xjCnwiBwftR17sr0spYcOpqET ZGcAmyYcNjy6CYadNCnfR40vhhWuCfNCBzWnUW0lFoo12wb0YnzoOLjvfD6OL3JjIUJNOmJy RCsJ5IA/Iz33RhSVRmROu+TztwuThClw63g7+hoyewv7BemKyuU6FTVhjjW+XUWmS/FzknSi dAG+insr0746cTPpSkGl3KAXeWDGJzve7/SBBfyznWCMGaf8E2P1oOdIZRxHgWj0zNr1+ooF /PzgLPiCI4OMUttTlEKChgbUTQ+5o0P080JojqfXwbPAyumbaYcQNiH1/xYbJdOFSiBv9rpt TQTBLzDKXok86M7BTQRS4TZ/ARAAkgqudHsp+hd82UVkvgnlqZjzz2vyrYfz7bkPtXaGb9H4 Rfo7mQsEQavEBdWWjbga6eMnDqtu+FC+qeTGYebToxEyp2lKDSoAsvt8w82tIlP/EbmRbDVn 7bhjBlfRcFjVYw8uVDPptT0TV47vpoCVkTwcyb6OltJrvg/QzV9f07DJswuda1JH3/qvYu0p vjPnYvCq4NsqY2XSdAJ02HrdYPFtNyPEntu1n1KK+gJrstjtw7KsZ4ygXYrsm/oCBiVW/OgU g/XIlGErkrxe4vQvJyVwg6YH653YTX5hLLUEL1NS4TCo47RP+wi6y+TnuAL36UtK/uFyEuPy wwrDVcC4cIFhYSfsO0BumEI65yu7a8aHbGfq2lW251UcoU48Z27ZUUZd2Dr6O/n8poQHbaTd 6bJJSjzGGHZVbRP9UQ3lkmkmc0+XCHmj5WhwNNYjgbbmML7y0fsJT5RgvefAIFfHBg7fTY/i kBEimoUsTEQz+N4hbKwo1hULfVxDJStE4sbPhjbsPCrlXf6W9CxSyQ0qmZ2bXsLQYRj2xqd1 bpA+1o1j2N4/au1R/uSiUFjewJdT/LX1EklKDcQwpk06Af/N7VZtSfEJeRV04unbsKVXWZAk uAJyDDKN99ziC0Wz5kcPyVD1HNf8bgaqGDzrv3TfYjwqayRFcMf7xJaL9xXedMcAEQEAAcLB XwQYAQgACQUCUuE2fwIbDAAKCRBlw/kGpdefoG4XEACD1Qf/er8EA7g23HMxYWd3FXHThrVQ HgiGdk5Yh632vjOm9L4sd/GCEACVQKjsu98e8o3ysitFlznEns5EAAXEbITrgKWXDDUWGYxd pnjj2u+GkVdsOAGk0kxczX6s+VRBhpbBI2PWnOsRJgU2n10PZ3mZD4Xu9kU2IXYmuW+e5KCA vTArRUdCrAtIa1k01sPipPPw6dfxx2e5asy21YOytzxuWFfJTGnVxZZSCyLUO83sh6OZhJkk b9rxL9wPmpN/t2IPaEKoAc0FTQZS36wAMOXkBh24PQ9gaLJvfPKpNzGD8XWR5HHF0NLIJhgg 4ZlEXQ2fVp3XrtocHqhu4UZR4koCijgB8sB7Tb0GCpwK+C4UePdFLfhKyRdSXuvY3AHJd4CP 4JzW0Bzq/WXY3XMOzUTYApGQpnUpdOmuQSfpV9MQO+/jo7r6yPbxT7CwRS5dcQPzUiuHLK9i nvjREdh84qycnx0/6dDroYhp0DFv4udxuAvt1h4wGwTPRQZerSm4xaYegEFusyhbZrI0U9tJ B8WrhBLXDiYlyJT6zOV2yZFuW47VrLsjYnHwn27hmxTC/7tvG3euCklmkn9Sl9IAKFu29RSo d5bD8kMSCYsTqtTfT6W4A3qHGvIDta3ptLYpIAOD2sY3GYq2nf3Bbzx81wZK14JdDDHUX2Rs 6+ahAA== In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 10/02/2025 9:29 pm, Julien Grall wrote: > Hi, > > On 08/02/2025 00:02, Andrew Cooper wrote: >> Right now, run_in_exception_handler() takes an input in an arbitrary >> register, >> and clobbers BUG_FN_REG.  This causes the compiler to calculate fn in >> the >> wrong regsiter. > > Just to confirm, you mean, the compiler is not clever enough to notice > that the value should be in the register BUG_FN_REG and therefore, two > registers will be clobbered. Is that correct? Not quite. The clobbered register set is always disjoint from inputs and outputs, so the combination of one clobbered + one input always means two different registers. For "here's an input but it gets modified", you need to express that as an output into a variable which isn't subsequently used. For ARM, that is best spelt "+r" (foo) so it can also be used with register asm() to tie to a single register.  On x86, you can use "=a" (tmp) : "a" (input).  In principle you can do it with named parameters, so [fn] "=r" (tmp) : "[fn]" (input) I believe works too. Here is a contrived example https://godbolt.org/z/WjqTKjWWb showing how the output (discard only) is forced into r0, causing the compiler to copy a into r3 around the asm block.  Notice that GCC and Clang pick the input operand differently, as both r0 and r3 are valid candidates in this case. However, for run_in_exception_handler(), "fn" isn't even modified (AFAICT), so it's correct to describe it as an input only. ~Andrew