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Date: Thu, 11 Jan 2018 10:47:59 +0100 From: Borislav Petkov <bp@...en8.de> To: Peter Zijlstra <peterz@...radead.org> Cc: "Woodhouse, David" <dwmw@...zon.co.uk>, "Thomas.Lendacky@....com" <Thomas.Lendacky@....com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>, "Ghitulete, Razvan-alin" <rga@...zon.com>, "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "ak@...ux.intel.com" <ak@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>, "riel@...hat.com" <riel@...hat.com>, "keescook@...gle.com" <keescook@...gle.com>, "gnomes@...rguk.ukuu.org.uk" <gnomes@...rguk.ukuu.org.uk>, "pjt@...gle.com" <pjt@...gle.com>, "dave.hansen@...el.com" <dave.hansen@...el.com>, "luto@...capital.net" <luto@...capital.net>, "jikos@...nel.org" <jikos@...nel.org>, "gregkh@...ux-foundation.org" <gregkh@...ux-foundation.org> Subject: Re: [PATCH] x86/retpoline: Fill return stack buffer on vmexit On Thu, Jan 11, 2018 at 10:32:31AM +0100, Peter Zijlstra wrote: > can't you do lovely things like: > > volatile asm ("call __fill_rsb_thunk_%1" : : "r" (dummy)) > > which would still let gcc select the register ? Calling a function from asm is nasty because you need to pay attention to clobbered registers as gcc doesn't see the function. What one can do, I *think*, is do a non-inlined wrapping function and do all the alternative_call() fun inside. There you can do all the fun and have callee-clobbered regs which you can use. -- Regards/Gruss, Boris. Good mailing practices for 400: avoid top-posting and trim the reply.
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