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Date: Mon, 29 Jan 2018 16:52:53 -0600
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Woodhouse <dwmw2@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
	Dave Hansen <dave.hansen@intel.com>,
	Ashok Raj <ashok.raj@intel.com>,
	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>,
	Jason Baron <jbaron@akamai.com>
Subject: Re: [PATCH 20/24] objtool: Another static block fail
Message-ID: <20180129225252.bi2etgk3eqprcv3x@treble>
References: <20180123152539.374360046@infradead.org>
 <20180123152639.170696914@infradead.org>
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On Tue, Jan 23, 2018 at 04:25:59PM +0100, Peter Zijlstra wrote:
> I've observed GCC generate:
> 
>   sym:
>      NOP/JMP 1f	(static_branch)
>      JMP 2f
>   1: /* crud */
>      JMP 3f
>   2: /* other crud */
> 
>   3: RETQ
> 
> 
> This means we need to follow unconditional jumps; be conservative and
> only follow if its a unique jump.
> 
> (I've not yet figured out which CONFIG option is responsible for this,
>  a normal defconfig build does not generate crap like this)
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Any chance we can just add a compiler barrier to the assertion macro and
avoid all this grow_static_blocks() mess?  It seems a bit... fragile.

-- 
Josh