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[209.85.167.53]) by smtp.gmail.com with ESMTPSA id w19sm2191241ljm.120.2020.07.02.14.55.36 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 02 Jul 2020 14:55:36 -0700 (PDT) Received: by mail-lf1-f53.google.com with SMTP id t74so17158362lff.2 for ; Thu, 02 Jul 2020 14:55:36 -0700 (PDT) X-Received: by 2002:ac2:5093:: with SMTP id f19mr19902332lfm.10.1593726935733; Thu, 02 Jul 2020 14:55:35 -0700 (PDT) MIME-Version: 1.0 References: <20200701184131.GI2786714@ZenIV.linux.org.uk> <20200701195914.GK2786714@ZenIV.linux.org.uk> <87lfk26nx4.fsf@mpe.ellerman.id.au> <20200702201755.GO2786714@ZenIV.linux.org.uk> <20200702205902.GP2786714@ZenIV.linux.org.uk> In-Reply-To: <20200702205902.GP2786714@ZenIV.linux.org.uk> From: Linus Torvalds Date: Thu, 2 Jul 2020 14:55:19 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: objtool clac/stac handling change.. To: Al Viro Cc: Michael Ellerman , Christophe Leroy , Josh Poimboeuf , Peter Zijlstra , "the arch/x86 maintainers" , Linux Kernel Mailing List Content-Type: multipart/mixed; boundary="000000000000dfc4eb05a97c77fc" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --000000000000dfc4eb05a97c77fc Content-Type: text/plain; charset="UTF-8" On Thu, Jul 2, 2020 at 1:59 PM Al Viro wrote: > > I'm not sure it's the right solution in this case. Look at the call chain > and the stuff done nearby (that __clear_user(), for example)... > > I'm not saying that this code is not awful - it certainly is. But it's > not that simple, unfortunately ;-/ Well, the minimal thing to do would probably be to just change that particular place to use asm_volatile_goto() for the error handling. Even aside from anything else, it would improve code generation and avoid that extra "err" variable. So something like this (ENTIRELY UNTESTED!!). It removes lines of code, and it must improve code generation too. And while XSTATE_OP() is still disgusting, it's (a) slightly less disgusting than it used to be (b) now easily fixable if we do the "exceptions clear AC" thing. so it's an improvement all around. If it works, that is. As mentioned: IT HAS NO TESTING. 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