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[209.85.167.48]) by smtp.gmail.com with ESMTPSA id v11-v6sm406945ljc.57.2018.11.29.11.12.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Nov 2018 11:12:08 -0800 (PST) Received: by mail-lf1-f48.google.com with SMTP id p6so2310516lfc.1 for ; Thu, 29 Nov 2018 11:12:07 -0800 (PST) X-Received: by 2002:a19:7013:: with SMTP id h19mr1937463lfc.147.1543518727041; Thu, 29 Nov 2018 11:12:07 -0800 (PST) MIME-Version: 1.0 References: <20181126160217.GR2113@hirez.programming.kicks-ass.net> <20181126200801.GW2113@hirez.programming.kicks-ass.net> <20181126212628.4apztfazichxnt7r@treble> <20181127084330.GX2113@hirez.programming.kicks-ass.net> <20181129094210.GC2131@hirez.programming.kicks-ass.net> <20181129143853.GO2131@hirez.programming.kicks-ass.net> <20181129163342.tp5wlfcyiazwwyoh@treble> <0A629D30-ADCF-4159-9443-E5727146F65F@amacapital.net> <20181129121307.12393c57@gandalf.local.home> <20181129124404.2fe55dd0@gandalf.local.home> <20181129125857.75c55b96@gandalf.local.home> <20181129134725.6d86ade6@gandalf.local.home> In-Reply-To: From: Linus Torvalds Date: Thu, 29 Nov 2018 11:11:50 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 4/4] x86/static_call: Add inline static call implementation for x86-64 To: Steven Rostedt Cc: Andy Lutomirski , Josh Poimboeuf , Peter Zijlstra , Andrew Lutomirski , "the arch/x86 maintainers" , Linux List Kernel Mailing , Ard Biesheuvel , Ingo Molnar , Thomas Gleixner , mhiramat@kernel.org, jbaron@akamai.com, Jiri Kosina , David.Laight@aculab.com, bp@alien8.de, julia@ni.com, jeyu@kernel.org, Peter Anvin Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 29, 2018 at 11:08 AM Linus Torvalds wrote: > > What you can do then is basically add a single-byte prefix to the > "call" instruction that does nothing (say, cs override), and then > replace *that* with a 'int3' instruction. Hmm. the segment prefixes are documented as being "reserved" for branch instructions. I *think* that means just conditional branches (Intel at one point used the prefixes for static prediction information), not "call", but who knows.. It might be better to use an empty REX prefix on x86-64 or something like that. Linus