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Date: Thu, 18 Jan 2018 16:31:31 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Borislav Petkov <bp@alien8.de>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>, linux-kernel@vger.kernel.org,
	Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andi Kleen <ak@linux.intel.com>,
	Arjan Van De Ven <arjan.van.de.ven@intel.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Jun Nakajima <jun.nakajima@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>
Subject: Re: [PATCH v2 07/10] x86/jump_label: Implement arch_static_assert()
Message-ID: <20180118153131.GG2249@hirez.programming.kicks-ass.net>
References: <20180116142825.376986833@infradead.org>
 <20180116143241.293294318@infradead.org>
 <20180118133322.ep66qnyedjl6qeiv@pd.tnic>
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On Thu, Jan 18, 2018 at 02:33:22PM +0100, Borislav Petkov wrote:
> On Tue, Jan 16, 2018 at 03:28:32PM +0100, Peter Zijlstra wrote:
> > Implement the static (branch) assertion. It simply emits the address
> > of the next instruction into a special section which objtool will read
> > and validate against either __jump_table or .altinstructions.
> > 
> > Use like:
> > 
> > 	if (static_branch_likely(_key)) {
> > 		arch_static_assert();
> > 		/* do stuff */
> > 	}
> > 
> > Or
> > 
> > 	if (static_cpu_has(_feat)) {
> > 		arch_static_assert();
> 
> It looks to me like the asserts can be moved into the macros and the
> assertion checking can happen by default ...?

Right until the point where someone writes:

	if (static_cpu_has(_feat) || ponies)

at which point it, rightfully, unconditionally asserts.

Not sure someone does that with static_cpu_has(), but there's
static_branch*() users that do exactly that.